<?xml version="1.0" encoding="UTF-8"?><rss version="2.0"><channel><title><![CDATA[Poultry Pro - Comprehensive poultry related articles and resources]]></title><description><![CDATA[Articles]]></description><link>http://www.poultrypro.com/poultry-articles/</link><copyright><![CDATA[Copyright Poultry Pro - Comprehensive poultry related articles and resources]]></copyright><generator>sNews CMS</generator><item><title><![CDATA[Feeding Programs for Egg-strain Pullets up to Maturity]]></title><description><![CDATA[  The major concern today with feeding and managing laying hens, is achieving desired weight for- age in the pullet, and especially during the early growth period. Genetic selection has been for reduced body weight in these birds, in order to improve feed efficiency, but a consequence of this is reduced feed intake. Ensuring that birds consume sufficient nutrients daily is made even more difficult when ingredient quality is poor and birds are subjected to heat stress or disease situations. The pullet manager must be skilful in managing diets and the environment, such that pullets consume an adequate level of nutrients up to maturity. While such nutrient intake varies with strain and environment, goals are around 800g crude protein and 18 Mcal ME consumed up to 18 weeks of age.            
          Diet specifications for pullets are shown in Table 1.   
  
    Feeding Management Of Growing Pullets     
    A. General Considerations     
It is generally agreed that most Leghorn and brown egg strains have changed over the last five to 10 years, and because of this, nutritional management is becoming more critical. In essence, these changes relate to age at maturity, although it is questionable that this has changed suddenly in just a few years. In fact, what has been happening is that age of maturity has slowly been decreasing by about one day per year. Unfortunately, many producers are just now becoming aware of earlier maturity because their conventional programs are no longer working, and this is especially true for many strains of brown egg pullets. Moving birds to laying cages at 21-22 weeks is no longer feasible, and this now invariably results in management problems. Similarly, first egg appearing at 16-18 weeks means that we must critically review our rearing programs. The key to successful nutritional management today is through maximizing body weight of the pullet. Pullets that are on target or slightly above target weight at maturity will inevitably be the best producing birds for the shell-egg market.   
  The traditional concern with early maturity has been that it results in small egg size. Results from our early studies indicate the somewhat classical effect of early maturity in Leghorns without regard to body weight (Table 2).   
      
  There seems little doubt that body weight and/or body composition are the major factors influencing egg size both at maturity and throughout the remainder of the laying period. Summers and Leeson (1983) concluded that body weight is the main factor controlling early egg size (Table 3).   
      
  We concluded that although there is evidence to indicate that nutrients such as protein, methionine and linoleic acid can influence egg size throughout the laying cycle, these nutrients have little effect on early egg size. This is probably related to the pullet producing at maximum capacity at least up to the time of peak egg mass.   
  Although it is fairly well established that body weight is an important criterion for adequate early production, there is still insufficient evidence regarding optimum body structure and composition. Frame size is being discussed, and is now most frequently included in breeder management guides as a form of monitoring. It is known that most (90%) of the frame size is developed early, and so by 12-16 weeks of age, the so-called &quot;size&quot; of the pullet is fixed. While this parameter is useful as another monitoring tool and its measurement should be encouraged, we have had little success in affecting frame size without also affecting body weight. It therefore seems very difficult to produce, by nutritional modification, pullets that are below target weight yet above average frame size and vice versa. The relationship between body weight and shank size is further complicated by the fact that environmental temperature also affects bone length independent of nutrition.   
  It would appear that early maturing chickens reach sexual maturity at significantly younger ages, but at similar body weights compared to later maturing birds. It seems as though early maturing birds achieve a threshold level of body mass and commence production when the minimum physiological age is reached, while late maturing birds at the same age do not have the body mass required for production. Recent reports have indicated the requirement of a certain lean body mass prior to onset of maturity. With most mammals, attainment of minimum fat reserves are essential for puberty, and so it seems likely that body composition is as important as total body mass in influencing the onset of egg production. In studies involving a relatively small number of birds, we have seen no correlation between age at first egg and either percentage or absolute levels of body fat. While no clear picture has yet emerged with respect to body composition and maturity, it seems likely that birds having some energy reserve as they approach peak egg production are less prone to subsequent problems. Too frequently, a production curve as shown in Figure 1 is observed with commercial flocks.   
  Our experience suggests that if this type of production loss is not due to an identifiable disease and/or management problem, then it most likely relates to birds being deficient in energy. It is perhaps not too surprising that birds are in such a precarious situation with respect to energy balance. Most mammals such as cows and sows must lose body weight during peak lactation in order to meet energy requirements. Perhaps the most classical case of energy deficiency at this time is seen with the turkey breeder. Due to a decline in feed intake from time of first lighting through to peak egg production, the turkey breeder necessarily loses considerable body mass in an attempt to maintain energy balance. It is likely that the same situation applies to both the Leghorn and modern brown egg type pullet. Obviously, the effect is most pronounced for underweight flocks with small appetites where energy intake is minimal. In fact, with many flocks exhibiting production characteristics as shown in Figure 1, it is body weight at housing that deserves immediate investigation rather than factors occurring later at the time of the production loss.   
  The key to solving many of our present industry problems would therefore seem to be attainment of &quot;heavy&quot; pullets at desired age of maturity. In this instance, &quot;heavy&quot; refers to the weight and condition which will allow the bird to progress through maturity with optimum energy balance. It is likely that such conditions will be a factor of the flock in question, being influenced by stocking density, environmental temperature, feather cover, etc. Unfortunately, attainment of desired weight for age has not always proven easy, especially where earlier maturity is desired or when adverse environmental conditions prevail. Leeson and Summers (1981) suggested that energy intake of the pullet is the limiting factor to growth rate, since regardless of diet specifications; pullets seem to consume similar quantities of energy (Table 4). 
  
  All of these birds were of comparable weight even though diet specifications were dramatically variable. As seen in Table 4, birds consumed similar quantities of energy, even though protein intake varied by 85%. These data suggest that if adequate protein intake is achieved, additional diet protein does little to stimulate growth rate.   
  In more recent studies, we have reared Leghorn pullets on diets varying in protein or energy, and again, energy intake seems to be the major factor influencing body weight (Tables 5 and 6).         
  These studies indicate the growth rate is more highly correlated with energy intake than with protein intake. This does not mean to say that protein (amino acid) intake is not important to the growing pullet. Protein intake is very important, but there does not seem to be any measurable return from feeding more than 800g of protein to the pullet through 18 weeks of age. On the other hand, it seems as though the more energy consumed by the pullet, the larger the body weight at maturity. Obviously, there must be a fine line between maximizing energy intake and creating an obese pullet.   
    
  
    B. Maximizing Nutrient Intake     
If one calculates expected energy output in terms of egg mass and increase in body weight, and relates this to feed intake, then it becomes readily apparent that the Leghorn must consume at least 90g/bird/day and the brown egg bird close to 100g/bird/day at peak production. With egg-type stock, feeding is related to appetite and so our management programs must be geared to stimulating appetite. The practical long-term solution is to rear birds with optimum body weight and body reserves as they begin production. This situation has been aggravated in recent years, with the industry trend of attempting to rear pullets on minimal quantities of feed. Unfortunately, this move has coincided with genetically smaller body weights and hence smaller appetites, together with earlier sexual maturity.   
  In order to maximize nutrient intake, one must consider relatively high nutrient dense diets, although these alone do not always ensure optimum growth. Relatively high protein (16-18% CP) with adequate methionine (2% CP) and lysine (5% CP) levels together with high energy levels (2800-3000 kcal/kg) are usually given to Leghorn pullets, especially in hot weather situations. However, there is some evidence to suggest that high energy diets are not always helpful under such warm conditions. This situation may relate to stimulation of nutrient intake when lower energy diets are fed at high temperatures (Table 7). In this recent study, Leghorn pullets were heavier at 126 days when fed the high energy diet in the cool environment, but diet had no effect at 30°C. As expected, pullets ate less of the high energy diet, and because all other nutrient levels were fixed, this results in reduced intake of all nutrients except energy. Pullets therefore ate less protein and amino acids when fed 3000 vs 2500 kcal ME/kg, and this can be critical where intake per se is less at 30°C. The pullets fed 3000 kcal/kg are borderline in intake of balanced protein at 870g versus our requirement for 800 g to this age. High energy diets may therefore not always be beneficial under heat stress conditions, and intake of other nutrients such as protein and amino acids must be given priority during formulation.   
  The Leghorn pullet eats for energy requirement, albeit with some imprecision, and so energy:protein balance is critical. All too often, we see inadequate amino acid intake when high energy corn-based diets are used, the result of which is pullets that are both small and fat at maturity.   
  One of the most important concepts today in pullet feeding, is to offer diets according to body weight and condition of the flock, rather than according to age. For example, traditional systems involve feeding starter diets for about six weeks followed by grower and then perhaps developer diets. This approach does not take into account individual flock variation, and today this can be most damaging to underweight flocks. It is becoming more difficult to attain early weight for age. This means that flocks are often underweight at four to six weeks of age. This can be for a variety of reasons such as sub-optimal nutrition, heat stress, disease, etc. The worse thing that can happen to these flocks is an arbitrary introduction of a grower diet, merely because the flock has reached some set age. Today, we must feed the higher nutrient dense starter until the target weight is reached. For example, Figure 2 shows an underweight flock at six weeks.   
  To change this flock to a grower at six weeks of age will cause problems because the flock will likely stay small until maturity, then be late maturing and produce a sub-optimal number of eggs that will also be small. This type of flock can most effectively be &quot;corrected&quot; by prolonged feeding of the starter diet. In this situation, the birds reach the low end of the guide weight at almost 10 weeks of age (Fig. 2). At this time, a grower diet could be introduced. Since the flock is showing a growth spurt, then feeding to almost 12 weeks could be economical – we now have a flock that is &quot;heavy&quot;. We have therefore converted the flock from being underweight and a potential problem, to one that is slightly over weight and so ideally suited to realizing maximum genetic potential during peak production. Some producers, and especially contract pullet growers, are sometimes reluctant to accept this type of program, since they correctly argue that feeding a high protein diet for 10-12 weeks will be more expensive. Depending upon local economic conditions, feeding an 18% protein starter diet for 12 versus six weeks of age, will cost the equivalent of two eggs. A bird in ideal condition at maturity will produce far in excess of these two eggs relative to a small underweight bird at maturity.   
      
  
    C. Suggested Feeding Program     
The following schedule is recommended for growing pullets to maturity:   
  Starter 18-19%CP; 2750-2900 kcal ME/kg   
  Day old _____________Target body weight   
  Grower 15-16%CP; 2750-2900 kcal ME/kg   
  Target wt ____________Mature body size   
    
  Pre-lay or layer 16-18%CP; 2750-2900 kcal ME/kg   
  Mature body size __________1st egg   
  As previously indicated, we are not making recommendations regarding age or even dictating the body weight at which diet changes should occur. Rather, the recommendations dictate the need for flexibility and the treatment of each flock as an individual case. For example, the starter diet is to be used until target weight for age is achieved. Hopefully, this will be at around 450g when the Leghorn bird is six to eight weeks of age. However, each flock will be subjected to varying environmental conditions, and so this may vary. The time of change to a lower-nutrient dense diet is when a desired weight-for-age is achieved, which we suggest is a weight that will be towards the top side of the breeder’s growth curve. Changing at a specific weight, or a specific age in isolation can lead to disastrously underweight flocks.   
  In our recommendations, we suggest the lower-nutrient dense grower diets to be fed from this target weight-for-age up until the desired mature body size is achieved. Again, we are not dictating a specific mature body weight, since this may be varied at the desire of the pullet grower (see following section). Pre-lay diets should only be used in an attempt at conditioning the calcium metabolism of the bird (see following section) and not as a means of initiating catch-up growth. Such growth spurts rarely occur at this age, and as such, pre-lay diets are being used as a &quot;crutch&quot; for poor rearing management.   
  An argument that is often heard about the role of body weight at maturity is that it is not, in fact, too important, because the pullet will show catch up growth prior to first egg ie: if the pullet is small, it will take a few days longer to mature, and start production at the &quot;same weight&quot;. This does not seem to happen, as small birds at 18 weeks are smaller at first egg (Table 8).         
  These data suggest that the smaller pullet does show some compensatory growth to the time of the first egg, although this is insufficient to allow for total &quot;catch-up&quot; growth. It is also interesting to note the relationship between body weight and age at first egg, and also between body weight and size of first egg. In other studies, we have followed up on the growth of the pullet through a production cycle in relation to 18-week (immature) body weight. Again, there is a remarkably similar pattern of growth for all weight groups indicating that immature weight seems to &quot;set&quot; the weight of the bird throughout lay (Figure 3).   
  Most importantly from a production viewpoint, is the performance of birds shown in Figure 3. When the lightest weight birds were fed diets of very high nutrient density (20% CP, 3000 kcal ME/kg) they failed to match egg production and egg size of the largest weight pullets that were fed very low nutrient dense diets (14% CP, 2600 kcal ME/kg). These results emphasize the importance of body weight in attaining maximum egg mass output.   
  The actual body weights to be achieved during rearing will obviously vary with breed and strain. Most Leghorn strains should weigh around 400g, 900g and 1300g at six, 12 and 18 weeks respectively. Similarly, the brown egg birds should weigh around 500g, 1000g and 1500g at these ages. As a rule of thumb, these weights for age can be used as guidelines for anticipated diet change.   
  Discussion to date has focused on the role of body weight and appetite of the growing pullet. While rearing programs such as reverse-protein (Leeson and Summers, 1979) have application where delay in maturity is required (usually due to inadequate light control) nutritional management programs today must allow for maximum early growth so as to attain breeder’s recommended weight goals as soon as possible. This type of nutritional management obviously entails accurate monitoring of body weight, a task that has too often been neglected with Leghorn pullets.   
    
  
    D. Manipulation Of Mature Body Size     
  In the preceding discussion, we have outlined the importance of maximizing body weight at sexual maturity, and the reasons for this have been explained. Under certain conditions, it is realized that some tempering of mature body size may be economically advantageous. Because body size has a dramatic effect on egg side, large birds at maturity can be expected to produce large eggs throughout their laying cycle. Depending upon the pricing of various egg grades, a very large egg may be uneconomical to produce, and in most instances, tempering of egg size of birds at 40-65 weeks of age is often difficult to do without some accompanying loss in egg numbers. Because body weight controls feed intake and egg size, an easier way of manipulating life-cycle egg size is through the manipulation of mature body size. If the maximum possible egg size is desired, then efforts must be made to realize the largest possible mature weight. However, where a smaller overall egg size is economical, then a smaller pullet is desirable. Such light weight pullets can be achieved by growing birds slower through the growth cycle, or more economically by light-stimulating pullets at an earlier age.   
    
  
    E. Pre-lay Nutrition     
Pre-lay diets are often used to try and manipulate body size or to bring about a transitional change in the birds calcium metabolism prior to maturity.   
      1. Pre-lay calcium       
There is still considerable confusion and variation practised in the levels of calcium given to birds prior to egg production. During the laying cycle, the bird utilizes its medullary bone reserves, in the long bones of the leg, to augment its diet supply when a shell is being formed. Because egg production is an &quot;all or none&quot; event, the production of the first egg obviously places a major strain on the bird’s metabolism, when it has to contend with a sudden 2g loss of calcium from the body. Some of this calcium will come from the medullary bone, and so the concept has arisen of building up this bone reserve prior to first egg. This obviously means higher levels of calcium in pre-lay diets. There are basically three options for calcium feeding around the time of maturity.   
  i. Use of 1% calcium grower diets until around 5% egg production   
  As previously mentioned, the largest weight pullets in a flock will likely mature earlier, and so it is these birds that may be disadvantaged with inadequate levels of calcium at this time. If such birds receive a 1% calcium grower diet at the time they are producing their first few eggs, they will only have a sufficient calcium reserve to produce two to three eggs. At this time, they will likely stop laying, or less frequently continue to lay and exhibit cage layer fatigue. If these earlier maturing birds stop laying, they do so for four to five days, and then try to start the process again. The bird goes through very short clutches, when at this time she is capable of a very prolonged 30-40 egg first clutch. Advocates of prolonged feeding of grower diets suggest that it makes the bird more efficient in the utilization or absorption of calcium, such that when she is eventually changed to a layer diet, improved efficiency continues for some time, and so the bird has large quantities of calcium available for shell synthesis. Figure 4 indicates that percentage calcium absorption from the diet does decline with an increased level of calcium in the diet.         
  However, there is no scientific evidence to suggest that efficiency of utilization is affected, and in fact calculations from Figure 4 indicate that as the calcium level in the diet is increased, calcium retention increases even though percentage retention has declined.   
  If 1% calcium grower diets are used as pullets mature, these diets should not be used after appearance of first egg, and to 0.5% production at the very latest. It must be remembered that under commercial conditions, it is very difficult to precisely schedule diet changes, and so decisions for diet change need to precede actual time of diet change, such that production does not reach 5-10% before birds physically receive the calcium enriched diets.   
  ii. Use of 2% calcium pre-lay diets   
  Specialized pre-lay diets are a compromise, in that they provide more calcium than do most grower diets, but still not enough for sustained production. The concept of using so-called pre-lay diets is to build up the medullary reserves without adversely influencing general mineral metabolism. However, as previously discussed with grower diets, 2% calcium pre-lay diets are inadequate for sustained egg production, and should not be fed past 1% egg production. The main disadvantage of pre-lay diets is that they are used for a short period of time, and many producers do not want the bother of handling an extra diet at the layer farm. There is also reluctance by some producers with multiage flocks at one site to use pre-lay diets, where delivery of diets with 2% calcium to the wrong flock on site can have disastrous effects on production.   
  iii. Early introduction of 3.5 - 4.0% calcium layer diets   
  In terms of calcium metabolism, the most effective program is early introduction of the layer diet. Such high calcium diets allow sustained production of even the earliest maturing birds. As previously mentioned, higher calcium diets fed to immature birds, lead to reduced percentage retention, although absolute retention is slightly increased (Table 9).   
  Feeding layer diets containing 3.5% calcium prior to first egg, therefore results in a slight increase in calcium retention of about 0.16 g/day relative to birds fed 0.9% calcium grower diets at this time. Over a 10-day period, however, this increased accumulation is equivalent to the output in one egg.   
  Early introduction of layer diets is therefore beneficial in terms of optimizing the calcium balance of the bird. However, there has been some criticism leveled at this practice. There is the argument that feeding excess calcium prior to lay imposes undue stress on the bird’s kidneys, since this calcium is in excess of the immediate requirement and must be excreted. In the study detailed in Table 9, we do show increased excreta calcium. However, kidney histology from these birds throughout early lay revealed no changes due to pre-lay calcium feeding. Recent evidence suggests that pullets must be fed a layer diet from as early as six to eight weeks of age before any adverse effect on kidney structure is seen (see following section on urolithiasis). It seems likely that the high levels of excreta calcium shown in Table 9 reflect fecal calcium, suggesting that all excess calcium may not even be absorbed into the body, merely passing through the bird with the undigested feed. This is perhaps too simplistic a view, since there is other evidence to suggest that excess calcium may be absorbed by the immature bird at this time. Such evidence is seen in the increased water intake and excreta water content of birds fed layer diets prior to maturity.         
  Early introduction of a layer diet seems to result in increased water intake, and a resultant increase in excreta moisture. Unfortunately, this increased water intake and wetter manure seems to persist throughout the laying cycle of the bird (Table 10).   
  These data suggest that birds fed high calcium layer diets during the pre-lay period will produce manure that contains 4-5% more moisture than birds fed 1% calcium grower or 2% calcium pre-lay diets. There are reports of this problem being most pronounced under heat stress conditions. A 4 to 5% increase in manure moisture may not be problematic under some conditions, although for those farms with a chronic history of wet layer manure, this effect may be enough to tip the balance and produce a problem.   
  In summary, the calcium metabolism of the earliest maturing birds in a flock should be the criterion for selection of calcium levels during the pre-lay period. Prolonged feeding of low-calcium diets is not recommended. Early introduction of layer diets is ideal, although where wet manure may be a problem, a 2% calcium prelay diet is recommended. There seems to be no problem with the use of 2% calcium prelay diets, as long as birds are consuming a high calcium layer diet not later than 1% egg production.   
  
      2. Pre-lay Body Weight And Composition       
Pre-lay diets are often formulated, and used, on the assumption that they will improve body weight and/or composition, and so correct problems arising with the previous growing program. Body weight and body condition should not really be considered in isolation, although at this time we do not have a good method of readily assessing body condition in the live pullet. For this reason, our main emphasis at this time is directed towards body weight.   
  The most important criterion used during rearing is pullet body weight as described previously. Each strain of bird has a characteristic mature body weight that must be reached or surpassed for adequate egg production and egg mass output. In general, pre-lay diets should not be used in an attempt to manipulate mature body size. The reason for this is that for most flocks, it is too late at this stage of rearing to meaningfully influence body weight - all too often, pre-lay diets are used as a crutch for poor rearing management.   
  However, if underweight birds are necessarily moved to a layer house, then there is perhaps a need to manipulate body weight prior to maturity. With black-out housing, this can sometimes be achieved by delaying photostimulation - this option is becoming less useful in that Leghorns and brown egg strains seem now to be maturing early without any light stimulation. If pre-lay diets are then necessarily used in an attempt to correct rearing mismanagement, then it seems as though the bird is most responsive to energy. This fact likely fits in with the effect of estrogen on fat metabolism, and the significance of fat used for liver and ovary development at this time. While such high nutrient density pre-lay diets may be useful in manipulating body weight, it must be remembered that this late growth spurt (if it occurs) will not be accompanied by any meaningful change in skeletal growth. This means that in extreme cases, where birds are very small in weight and stature at approximately 16 -18 weeks of age, then the end result of using high-nutrient dense pre-lay diets may well be pullets of correct body weight, but of small stature. These short shank length pullets seem more prone to prolapse/pickout, and so this is another example of the limitations in use of classical pre-lay diets.   
  While body composition at maturity may well be as important as body weight at this age, it is obviously a parameter that is difficult to quantitate. There is no doubt that energy is likely the limiting nutrient for egg production for all strains of bird, and around peak production, feed may not be the sole source of energy. Labile fat reserves at this time are therefore, essential to augment feed sources that are inherently limited by low feed intake. These labile fat reserves become critical during situations of heat stress or general hot weather conditions. Once the bird starts to produce eggs, then its ability to deposit fat reserves is greatly limited. Obviously if labile fat reserves are to be of significance, then they must be deposited prior to maturity. As with most classes of bird, the fat content of the pullet can best be manipulated through changing the energy:protein balance of the diet. If labile fat reserves are thought necessary, then high energy, high fat pre-lay diets should be considered. As previously stated, this scenario could well be beneficial if peak production is to coincide with periods of high environmental temperature.   
  The requirements for a specific body composition at the onset of maturity have not been adequately established. With mammals, onset and function of normal estrus activity is dependent on the attainment of a certain body fat content. In humans for example, onset of puberty will not occur if body fat content is less than around 14%. No such clear cut relationship has emerged with egg layers. Work conducted with broiler breeders, in fact indicate a more definite relationship between lean body mass and maturity, rather than fat content and maturity.   
  
      3. Subsequent Egg Weight And Egg Composition       
It seems as though egg size is ultimately controlled by the size of the yolk that enters the oviduct. In large part this is influenced by body weight of the bird, and so factors described previously for body weight can also be applied to concerns with egg size. There is a general need for as large an early egg size as is possible, especially with breeder hens. Most attempts at manipulating early egg size have met with limited success. Increased levels of linoleic acid in prelay diets may be of some use, although levels in excess of the usual 1% found in most diets produce only marginal effects on early egg size. From a nutritional standpoint, egg size can best be manipulated with diet protein, and especially methionine concentration. It is logical, therefore to consider increasing the methionine levels in pre-lay diets.   
  For breeder hens, one also has to consider egg composition in relation to successful embryo development. It is well known that hatchability of eggs from young breeders is lower. The reasoning for this suboptimal hatch seems to relate to &quot;maturity&quot; of embryonic membranes, and movement of nutrients from the yolk and albumen to the embryo. However, part of this problem may also relate to inadequate passage of certain nutrients from the breeder hen into the egg. For example, it is known that young breeders do not deposit normal quantities of biotin into the egg - normal biotin concentration in the egg is apparently not achieved until production of the 8 - 10th egg. If this is a general effect with a number of key nutrients, then it would seem worthwhile to study the effect of pre-lay nutrient intake on egg composition in relation to embryonic needs.   
  
      4. Pre-pause      
In recent years, there has been interest in some countries of so-called pre-pause feeding programs. The idea behind these programs is to withdraw feed, or feed a very low nutrient dense diet at time of sexual maturity. This somewhat unorthodox program is designed to &quot;pause&quot; the normal maturation procedure, and at the same time to stimulate greater egg size when production resumes after about 10-14 days. This type of pre-lay program is therefore most beneficial where early small egg size is undesirable.   
  Pre-pause can be induced by simply withdrawing feed, usually at around 1% egg production. Under these conditions, pullets immediately lose weight, and fail to realize normal weight-for-age when refed. Egg production and feed intake normalize after about 22 weeks, although there is 1-1.5g increase in egg size. Figure 5 shows the production response of Leghorn pullets fed only wheat bran from 18 weeks (1% egg production) through to 20 weeks of age. This data is presented on an equalized physiological basis, rather than equal age basis.   
  The most noticeable effects of a pre-pause diet such as wheat-bran, are very rapid attainment of peak egg production and an increase in egg size once re-feeding commences. These effects (Figure 5) are undoubtedly due to increased feed intake. This management system could therefore be used to better synchronize onset of production (due to variance in body weight), to improve early egg size or to delay production for various management related decisions. The use of such pre-pause management will undoubtedly be affected by local economic considerations.         
  
      5. Urolithiasis       
Kidney dysfunction often leads to problems such as urolithiasis, and this most commonly occurs during the late growing or early egg production phase of the pullet. While infectious bronchitis can be a confounding factor, urolithiasis is most often induced by diet mineral imbalance in the late growing period. At post-mortem, often one kidney is found to be enlarged and contain mineral deposits known as uroliths. Some outbreaks are correlated with a large increase in diet calcium and protein in layer versus grower diets, coupled with the stress of physically moving pullets at this time, and being subjected to a change in the watering system (usually onto nipples in the laying cages). The uroliths are most often composed of calcium-sodium-urate.   
  The occurrence is always more severe when growing pullets are fed high calcium diets for an extended period prior to maturity. For example, urolithiasis causing 0.5% weekly mortality, often occurs under experimental conditions when pullets are fed layer diets after 10-20 weeks of age (relative to maturity at 18-19 weeks). However there is no indication that early introduction of a layer diet for just two to three weeks prior to maturity is a causative factor.   
  Because diet electrolytes can influence water balance and renal function, it is often assumed that an electrolyte excess or deficiency may be predisposing factors in urolithiasis or gout. Because salts of uric acid are very insoluble, then the excretion of precipitated urate salts could serve as a water conversation mechanism, especially when cations are excreted during salt loading or when water is in short supply. When roosters are given saline water (1% NaC1) and fed high-protein diets, uric acid excretion rates are doubled relative to birds offered the high protein diet al.,ong with non-saline drinking water. Because uric acid colloids are negative charges, they attract cations such as Na, and so when these are in excess, there is an increased excretion via urates, presumably at the expense of conventional NH4 compounds. There is some evidence of an imbalance of Na+K-C1 levels influencing kidney function. When excess Na+K relative to C1 is fed, a small percentage of the birds develop urolithiasis. It is likely that such birds are excreting a more alkaline urine, a condition which encourages mineral precipitation and urate formation.   
  Urolithiasis therefore seems to be most problematic in laying hens fed high levels of calcium well in advance of sexual maturity. Although the situation is often confounded with IBV infection, it seems obvious that no more than 1% calcium should be fed to Leghorn birds prior to maturity. Feeding prelay (2% Ca) or layer diets containing 3% calcium for two to three weeks prior to first egg is not problematic, and surprisingly, uroliths rarely form in adult male breeders fed high calcium diets. High levels of crude protein will increase plasma uric acid levels, and potentially provide conditions conducive to urate formation. Certainly numerous mycotoxins influence kidney function, and so general mill management regarding quality control and/or use of feed additives to suppress their harmful effects would likely be beneficial.   
  In humans at least, urolith formation can be controlled by adding urine acidifiers to the diet. Studies with pullets show similar advantages. Adding 1% NH4C1 to the diet results in a more acidified urine, and uroliths rarely form under these conditions. Unfortunately, this treatment results in increased water intake and associated wet manure. One of the potential problems in using NH4C1 in laying hens, is that it induces a metabolic acidosis and this is detrimental to egg shell quality especially under conditions of heat stress. Such treatment also assumes the kidney can clear the increased load of H+, and for a damaged kidney, this may not always occur. As a potential urine acidifier without such undesirable side effects, several researchers have studied the role of Alimet® a methionine analogue. From five to17 weeks of age, pullets were fed diets containing 1 or 3% calcium in combination with 0, 0.3 or 0.6% Alimet®. Birds fed the untreated high calcium diet excreted alkaline urine containing elevated calcium concentrations together with urolith formation and some kidney damage. Feeding 0.6% Alimet® acidified the urine, but did not cause a general metabolic acidosis. Alimet® therefore reduced kidney damage and urolith formation without causing acidosis or increased water consumption.   
  It is concluded that urine acidification can be used as a prevention or treatment of urolithiasis, and that this can be accommodated without necessarily inducing a generalized metabolic acidosis. From a nutritional viewpoint, kidney dysfunction can be minimized by not oversupplying nutrients such as calcium, crude protein and electrolytes for too long a period prior to maturity.   
  
      F. Brown-egg Pullets       
There is very little information available on specific nutrient needs of brown egg pullets, and whether or not they need diets any different to those used for white egg birds. It is generally assumed that white and brown egg pullets are similar in their nutrient needs relative to body weight. Brown egg pullets are usually heavier than white egg birds, although this difference seems to be decreasing over the last few years. For example, in the past it has been fairly common practice to start physical feed restriction after 10-12 weeks of age, in order to control growth rate. Today, with many strains of pullet, this feed restriction is unnecessary, and in fact may be detrimental in hot weather conditions. The principle of feeding management of brown egg pullets is essentially the same as described for the slightly smaller white egg bird as outlined in the previous sections. Achieving target weight-for-age must be the major criterion of the growing program, because this ensures the best chance of realizing the bird’s genetic potential as a layer.   
  If physical feed restriction is necessary, due to birds becoming overweight, then bird uniformity becomes a major concern. With a mild restriction program, birds can be allowed to &quot;run-out&quot; of feed one day per week and, usually this will do little harm to uniformity. If it is necessary to impose a greater degree of feed restriction, on a daily basis, then it is important to ensure rapid and even feed distribution, much as subsequently discussed for broiler breeders. Feed restriction should be relaxed if birds are subjected to any stresses such as beaktrimming, vaccination, general disease challenge or substantial reduction in environmental temperature. An alternative management procedure for overweight birds, is to schedule an earlier light stimulation and move to layer cages (see Fig. 3.4). There is an indication that young brown egg pullets may not adjust feed intake too precisely in response to adjusting diet energy level (Table 11).   
  As energy level is increased at a fixed protein level (Table 11), a reduction in growth rate is sometimes seen because protein and amino acid intake are limited. Brown egg pullets seems to change their feed intake very little under these conditions, and consequently there is improvement in growth rate. In another study, pullets were fed diets at 2750 or 3000 kcal ME/kg. Over the 126 days growing period, brown egg pullets consumed 6% more energy when fed the high energy diet (20.6 versus 19.4 Mcal). Contrary to this increased energy intake, white-egg pullets consumed about 18 Mcal ME regardless of energy level in the diet.         
  An alternative scenario in explaining these results is that the heavier brown-egg pullet has reduced amino acid needs, and so when fed high energy diets there is less effect on amino acid intake relative to needs. In a series of studies, we have shown the brown egg pullet to grow quite well on very low levels of lysine relative to that recommended by most breeders (Table 12).   
  Up to 42 days of age, the lysine requirement of the pullet seems to be 0.58 - 0.68% of the diet, which is substantially less than values of 0.9-1.0% as recommended by most breeders. From 84- 126 days during the later phases of growth, there was no response to growth rate with more than 0.46% diet lysine. These experimental results suggest that under moderate environmental temperatures, it may be inadvisable to use high energy diets for growing brown egg pullets. On the other hand, assuming their response to diet energy is independent of temperature, then it may be easier to stimulate growth of these pullets under heat stress conditions, simply by increasing the nutrient density of the diet.   
]]></description><pubDate>Thu, 22 Jul 2010 23:16:00 +0000</pubDate><link>http://www.poultrypro.com/poultry-articles/layers/feeding-programs-for-eggstrain-pullets-up-to-maturity/</link><guid>http://www.poultrypro.com/poultry-articles/layers/feeding-programs-for-eggstrain-pullets-up-to-maturity/</guid><author>Thu, 22 Jul 2010 23:16:00 +0000</author><comment></comment></item><item><title><![CDATA[Feeding Programs for Laying Hens: An Introduction]]></title><description><![CDATA[  With high egg output and reduced feed intake, packaging the required nutrients into the voluntary daily intake of the layer, has become increasingly more difficult. A balance of all nutrients is required for maximum egg mass output, although of these nutrients, energy intake is often a limiting nutrient. Even under heat-stress conditions, energy needs are often the limiting factor to maintaining good egg production, and achieving optimum egg size and eggshell quality. Protein and amino acid intake is obviously critical, although it is fairly easy to maintain intake of critical amino acids even at relatively low feed intake. On the other hand, it is more difficult to maintain energy intake, and much of this challenge relates to the fact that feed intake per se is largely controlled by energy needs. The bird will, therefore, adjust its feed intake with fair precision in response to changes in diet energy level. As the energy level of the diet increases, then birds eat less and vice versa with low energy diets, so that the bird maintains a relatively constant energy intake. It is fairly difficult to convince the bird to consume amounts of energy different to its &quot;requirement&quot;. Certainly higher-energy diets do fool the bird into eating more energy, but the response is small, and &quot;over consumption&quot; of energy is often quite small in relation to our expected needs for the bird. Table 1 shows diet specification for layers based on expected feed intake. There is a considerable range of daily feed intake patterns shown by laying hens, and so it is important to select and formulate diets based on expected feed intake, such that the daily intake of specified nutrients are achieved. The large range of daily feed intakes encountered with laying hens is caused by variation in age at sexual maturity, inherent body weight and environmental effects such as temperature and bird density.         
  Most Leghorn strains of bird will now start to mature on intakes of 80-85g/day, and it is quite difficult to formulate diets for these birds that will ensure adequate intakes of all nutrients. Meeting the bird’s energy needs is perhaps most critical at this time. Through the period of peak egg numbers, it is important that the bird not be deficient in energy, and so high, rather than low energy diets are usually preferred. However, energy level can be altered within reasonable limits, and the bird will adjust its feed intake accordingly. Maintaining the balance of other nutrients to energy is therefore an important concept in layer nutrition.   
  
    General Considerations In Feeding Layers     
The development of feeding programs for layers cannot be implemented without consideration of the rearing program. Unfortunately, many egg producers purchase point-of-lay pullets from independent pullet growers, and here the goals of the two producers are not always identical. Too often, the egg producer is interested in purchasing mature pullets at the lowest possible cost per bird regardless of its condition. For pullet growers to make a profit, they must produce a bird at the lowest possible cost. With feed representing some 60 to 70% of the cost to produce a pullet, the obvious way for the pullet grower to reduce costs is to save on feed. While they may be able to save a small amount of feed by eliminating feed waste or by ensuring that house temperatures are optimum, the only way to save a substantial amount of feed is to place the pullets on a growing program such that feed consumption is reduced and/or cheaper diets are used. Because it is not possible to enhance the efficiency with which pullets convert feed into body weight gain, the net result is a smaller bird going into the laying house. If the birds have been on an increasing light pattern, they might well be mature, as judged from appearance, at the onset of production. However, such pullets must still grow before they reach their optimum weight and condition as a laying hen. Consequently, the egg producer will have to feed this pullet so as to attempt to bring the body weight up to normal if a profitable laying flock is to be obtained. If egg producers attempt to save on feed, the result will be underweight birds at peak egg production. This situation leads to smaller eggs, and often lower than normal peaks or birds dropping relatively quickly in production shortly past peak as discussed in the previous chapter.   
  It takes a certain amount of feed to produce a laying hen with optimum body size. If this feed is not consumed in the growing period, it must be fed in the laying house. Of course, one would have to be sure that the pullets are healthy and are not carrying an excess of body fat. However, the problem of excess body fat with today’s modern type, early maturing pullet does not usually occur. Egg producers should also find out as much as possible about the pullets they are purchasing such as the type of feeding program they have been on, the health status of the flock, and the type of waterers used in rearing. With this type of information, they should be in a better position to turn the immature pullets into a profitable laying flock.   
  Over the last few years, it has become general practice to describe feeding programs for Leghorn birds according to the level of feed intake. It is well known that under normal environmental and management conditions, feed intake will vary with the egg production and/or age of bird, and this must be taken into account when formulating diets. While Leghorn may adjust intake according to diet energy levels, there is no evidence to suggest that such precision occurs with other nutrients.   
  The following daily intakes of nutrients are suggested under ideal management and environmental conditions (Table 2).         
  However, as feed intake changes, specifications must be modified in order to maintain this intake of nutrients. Table 3 gives an example of the type of specification changes necessary for various levels of feed intake. As a generalization, these changes are something of a compromise, since it is often difficult and uneconomical to go to the extreme specifications necessary with very low levels of feed intake. A knowledge of feed intake, and the factors that influence it, are therefore essential for any feed management program.         
  To a degree, the energy level of the diet will influence feed intake, although one should not assume the precision of this mechanism to be perfect. In general, birds over consume energy with higher energy diets, and they will have difficulty maintaining normal energy intake when diets of less than 2500 kcal ME/kg are offered. In most instances, under consumption rather than over-consumption is the problem, and so use of higher energy diets during situations such as heat stress will help to minimize energy insufficiency.   
  There is little doubt that body weight at maturity is a major factor influencing feed intake and so economic performance of laying hens. Body weight differences seen at maturity are maintained throughout the laying cycle almost regardless of nutrient profile of layer diets. It is therefore difficult to attain satisfactory nutrient intakes with small birds. Conversely, larger birds will tend to eat more, and this may become problematic in terms of the potential for obesity and/or too large an egg towards the end of lay. Phase feeding of nutrients can overcome some of these problems, although a more simplistic long term solution is control over body weight at maturity. Under most economic conditions, heavier birds at maturity are ultimately most economical for table egg production in terms of egg revenue relative to feed costs.   
  This whole situation of feed management is also being confounded with earlier and higher peaks from today’s strains of birds. Under these &quot;ideal&quot; situations, it is again energy insufficiency that can cause problems during post peak production. Egg production curves that show a 5 - 8% reduction after peak are characteristic of birds with insufficient appetite caused by too small a pullet at maturity. The reduction in appetite is of concern relative to the adequacy of energy intake. Calculations of energy balance indicate a somewhat precarious balance around the time of peak egg numbers, indicating the need for stimulating feed intake per se, and the possibility of providing some labile energy reserves in the form of carcass energy (fat) stores. Tables 3 and 4 show such calculated values for Leghorn and brown egg strains respectively, and relate these to the required intake of a standard diet.   
  The significance of energy intake as the limiting nutrient for egg production with modern strains of layer is shown in (Figure 1). There is a dramatic response to energy intake from 184-312 kcal/bird/day, in the form of egg output. At very high energy intakes, there is little apparent response to protein intake over the range of 13 - 21 g /bird/day.         
  Only when energy intake is limiting is there any measurable increase in egg numbers in response to increased protein intake. However, as will be detailed later, the converse applies in terms of egg size, when the bird shows a dramatic response to protein intake and little response to energy intake. Many problems associated with reduced nutrient intake of white egg layers can therefore be overcome by ensuring optimum body weight and appetite of young laying pullets.   
  Unfortunately, mean weight of the flock at this age is too often considered independently of flock uniformity. Pullets may be of &quot;mean&quot; body weight, yet be quite variable in weight, and often outside the accepted range of 85% of the flock being within +-10% of mean weight. The major problem with a nonuniform flock is variability in age at first egg, and so there is variability in feed intake. If diets are tailored to feed intake, then late maturing smaller birds (with small appetites) will likely be underfed. Conversely, large weight early maturing pullets with increased appetites may be overfed at this time. The consequence is often a delayed peak, and reduced overall egg production.   
  An argument against being overly concerned about uniformity is that birds will adjust their intake according to nutrient (energy) needs, and so early maturing birds will eat more, and late maturing birds less, during the early phases of production. However, if birds are given diets formulated on the basis of feed intake, this can lead to problems, the most serious of which is underfeeding of the larger early maturing bird. Another confounding factor, is that as birds mature within a flock, the percent production realized on a daily basis does not reflect the number of birds laying at that time. For example at about 40% production, there are in fact around 70% of the birds mature and requiring proportionally more nutrients than suggested by egg production alone. These differences become more pronounced as flock uniformity declines, and so this makes tailoring nutrient needs to feed intake and performance characteristics that much more difficult to achieve.   
]]></description><pubDate>Thu, 22 Jul 2010 23:08:00 +0000</pubDate><link>http://www.poultrypro.com/poultry-articles/layers/feeding-programs-for-laying-hens-an-introduction/</link><guid>http://www.poultrypro.com/poultry-articles/layers/feeding-programs-for-laying-hens-an-introduction/</guid><author>Thu, 22 Jul 2010 23:08:00 +0000</author><comment></comment></item><item><title><![CDATA[Feeding Programs for Laying Hens: Heat Stress]]></title><description><![CDATA[    An increasingly large proportion of the world’s laying hens are kept in areas where heat stress is likely to be a major management factor at some stage during egg production. Basically the problem relates to birds not consuming enough feed at this time, although there are also some subtle changes in the bird’s metabolism that affect both production and shell quality. While all types of poultry thrive in warm environments during the first few weeks of life, normal growth and development of older birds is often adversely affected. Obviously, the bird’s requirements for supplemental heat declines with age, because insulating feathers quickly develop and surface area in relation to body size is reduced. Heat stress is often used to describe bird status in hot environments, although it is obvious that more than just temperature is involved. Because birds must use evaporative cooling (as panting) to lose heat at high temperatures, humidity of inhaled air becomes critical. Thus high temperature and humidity together are much more stressful to birds than high temperature alone. Other environmental factors such as air speed and air movement also become important. It is also becoming clear that adaptation to heat stress can markedly influence bird response. For example, laying birds can tolerate constant environmental temperatures of 35°C and perform reasonably well. On the other hand, most birds are stressed at 35°C when fluctuating day/night temperatures are involved. In the following discussion, it is assumed that fluctuating conditions exist, since these are more common and certainly more stressful to the bird.     
        

  The main concern under hot weather conditions is the layer’s ability to consume feed. As poultry house temperature increases, then less heat is required to maintain body temperature and the birds consume less feed. In this situation, &quot;environmental&quot; energy is replacing feed energy and is economical. However, the relationship between body heat production and house temperature is not linear, since at a certain critical temperature, the bird’s energy demands are increased in order to initiate body cooling mechanisms. The following factors should be considered in attempting to accommodate heat stress.   
  
  A.   Bird’s Response To Heat Stress     
Figure 2 is a schematic representation of a heat stress effect. Minimal body heat production (and hence the most efficient situation) is seen at around 23°C. Below this temperature, (lower critical temperature) birds generally have to generate more body heat in order to keep warm.   
  However, there is only a narrow range of efficiency between 19-27°C, over which heat production is minimal. Above 27°C, birds start to use more energy in an attempt to stay cool. For example, at 27°C, birds will start to dilate certain blood vessels in order to get more blood to the comb, wattles, feet etc. in an attempt to increase cooling capacity. More easily observed by the egg producer is the characteristic panting and wing drooping that occurs at slightly higher temperatures. These activities at high environmental temperatures mean that the bird has an increased, rather than decreased, demand for energy. Unfortunately, the situation is not as clear cut as depicted in Figure 2, and this is likely the reason behind the variability seen in flock response to various environmental conditions. Rather than lower and upper critical temperature being rigidly fixed under all conditions, heat production is likely to fluctuate in response to a number of very practical on-farm conditions. Variation in response can be caused by such factors as a) increased feed intake, b) better feathering or c) increased bird activity. Such potential variability in bird response should be taken into account when interpreting the quantitative data discussed in Figures 3 and 4. The whole picture is further confused by the normal energy intake pattern of the bird (Figure 3). The base line shown in Figure 3 is a repeat of the temperature effect detailed in Figure 2.         
  The upper line of Figure 3 represents energy intake for a 1.5 kg layer. Again as environmental temperature increases, energy (feed) intake declines. However above 27-28°C, the decline becomes quite dramatic since the bird is changing its metabolic processes in response to the heat load, and actions such as panting, etc. adversely influence the feeding mechanisms in the brain and also reduce the time available for feeding. The shaded area between the lines in Figure 3, represents the energy available for production. As we approach and exceed the critical 28°C mark, then energy available for production is dramatically reduced and around 33°C actually becomes negative.   
  If the shaded area (available energy), in Figure 3 is itself plotted against temperature, then a clear pattern is seen with respect to potential for egg production (Figure 4). If we assume an average egg contains the equivalent of 80 kcal ME, then at 90% production, there is a daily need for around 70 kcal to meet needs for production alone. Our calculations from Figure 3 indicate total available energy at 90 kcal per day, and so we have a small positive difference that will likely go for growth or increased body weight. At 28°C, there is energy available only for eggs and none for growth. Above 28°C, available energy cannot meet energy demands for 90% egg production. Either egg production must be decreased, or other energy sources used. The bird’s body reserves (fat and muscle) could therefore be used at this time. These figures are not fixed and will likely vary with such factors as air speed, feathering etc. as previously detailed. However, for most flocks, these types of reactions, as depicted in Figure 4 are likely to occur at + 2°C of the values shown. In this scenario, the bird is in negative energy balance at 33°C (Figure 4). Various equations have been developed to relate energy intake to environmental temperature. For example, the equations given by NRC (1994) is ME(kcal/day) = W75 (173 - 1.95T) + 5.5 W + 2.07EE where W = body weight, kg; T = C, W = weight gain per day, g; and EE = daily egg mass, g. Solving this equation for environmental temperatures of 10-34°'a1C, shows an almost linear relationship for a 1.3 kg bird producing 50 g egg mass per day and gaining weight at 2 g per day (Fig. 5).   
  A major factor affecting this energy intake response to environmental temperature is feather cover, which represents insulating capacity for the bird. Coon and co-workers have developed equations that take into account degree of feathering. This equation is solved in Figure 6 for birds having 90, 75 or 60% feather cover. As expected, at low environmental temperatures, feather cover has a major effect on feed intake, while at 34°C which is close to body temperature; there is no effect of feather cover.   
  &nbsp;  
  B.   Energy Balance     
  Our main concern during heat stress therefore is the availability of energy for egg production. Optimizing such energy availability may be approached by either:   
  (i) Increasing diet energyspecifications   
  (ii) Stimulating feed intake or   
(iii) Considering body energy reserves   
  (i) It is well known that birds consume less feed as the energy level of the feed increases. This is because the bird attempts to maintain a given energy intake each day. However, the mechanism is by no means perfect, and as energy level is increased, the expected decline in feed intake is seldom achieved. This obviously leads to &quot;overconsumption&quot; of energy. Also, as environmental temperature increases, the mechanism seems less perfect. The following results are seen when diet energy level is increased from 2860 kcal ME/kg to 3450 kcal ME/kg (Table 5, Payne, 1967).         
  At 18°C, there is fairly good adjustment by the bird, such that feed intake is markedly reduced with high energy diets; this in an attempt to normalize energy intake. At high temperatures, birds adjust feed intake less perfectly, such that &quot;overconsumption&quot; of energy occurs. It is not suggested that these extremes of diet energy be used, rather that energy intake will be maximized with as high a diet energy level as is possible. In order to increase diet energy level, the use of supplemental fat should be considered. Dietary fat has the advantage of increasing palatability and also reducing the amount of heat increment that is produced during its utilization in the body.   
  (ii) Various methods can be tried to stimulate feed intake. Feeding more times each day usually encourages feeding activity. Feeding at cooler times of the day, if possible, is also a useful method of increasing nutrient intake. If artificial lights are used, it may be useful, under extreme environmental conditions, to consider a so-called midnight feeding, when temperature will hopefully be lower and birds are more inclined to eat. Again, where conditions are extreme, making the diet more palatable may be advantageous. Such practices as pouring vegetable oil, molasses, or even water, directly onto the feed in the troughs may encourage intake. Whenever high levels of fat are used in a diet, or used as a top dressing as described here, care must be taken to ensure that rancidity does not occur. This can best be achieved by insisting on the incorporation of quality antioxidants in the feed and that feed is not allowed to &quot;cake&quot; in tanks, augers or troughs. Fresh feed becomes critical under these conditions.   
  Diet texture can also be used to advantage. Crumbles tend to stimulate intake while a sudden change from large to small crumbles also has a transitory effect on stimulating intake. It is interesting to observe that a sudden change from small to large crumbles seems to have a negative effect on intake (Table 6).         
  (iii) It is now realized that correct pullet rearing programs are essential for optimum economic return in the layer house. This becomes very critical under hot weather conditions as the bird may have to rely on its body reserves to supplement energy required to maintain egg production. In general, the larger the body weight at maturity, the larger the body weight throughout lay, and hence the larger the potential energy reserve and the greater the feed intake. It is not suggested that extremely fat pullets are desirable, but it is obvious that birds of optimum weight with a reasonable fat reserve will likely stand up better to heat stress situations. Pullets that are subjected to heat-stress and have less &quot;available&quot; energy than that required to sustain production, have no recourse but to reduce egg mass output in terms of egg weight and/or egg numbers.   
  &nbsp;  
  C.   Protein Nutrition     
In the past, it has been common practice to increase protein levels during heat stress conditions. This has been done on the basis of reduced feed intake, and hence protein levels have been adjusted upwards in attempting to maintain intakes of around 17g crude protein/bird/day. It is now realized that such adjustments may be harmful. When any nutrient is metabolized in the body, the processes are not 100% efficient and as a result, some heat is produced. Unfortunately, protein is the most inefficiently utilized nutrient in this regard and so proportionately; more heat is evolved during metabolism of amino acids. The last thing that a heat stressed bird needs is additional waste heat being generated in the body. This extra heat production may well overload heat dissipation mechanisms (panting, blood circulation). We are therefore faced with a difficult problem of attempting to maintain &quot;protein&quot; intake in situations of reduced feed intake, yet we know that more crude protein may be detrimental. The answer to the problem is not to increase crude protein, but rather to increase the levels of essential amino acids. By feeding synthetic amino acids, we can therefore maintain the intake of these essential nutrients without loading up the body systems with excess crude protein (nitrogen). General recommendations are, therefore, to increase the use of synthetic methionine and lysine so as to maintain daily intakes of approximately 360 and 720mg respectively.   
  &nbsp;  
  D.   Minerals And Vitamins     
Calcium level should be adjusted according to anticipated level of feed intake, such that birds consume 3.5g per day. Under extreme conditions, this may be difficult since, as previously indicated, high energy diets are also desirable and these are difficult to achieve with the increased use of limestone or oyster shell. Table 7 shows the diet specifications needed to maintain intakes of Ca, P and vitamin D3, all of which are critical for eggshell quality.   
  Because it is also necessary to increase the energy level of the diet when feed intake is low, then it is counterproductive to add high levels of limestone and phosphates which effectively dilute the feed of all nutrients other than Ca and phosphorus. The problem of potential calcium deficiency is most often met by top dressing feed with oystershell or large particle limestone. The situation for phosphorus is more complex, and in fact it may be deleterious to use the high levels shown in Table 7. In practice, phosphorus levels are seldom increased to these extreme levels unless cage layer fatigue is an ongoing problem. The deficit of vitamin D3 is best met with use of D3 supplements in the drinking water.         
  There seems to be some benefit to adding sodium bicarbonate to the diet or drinking water. However, this must be done with care so as not to impose too high a load of sodium on the bird, and so salt levels may have to be altered. This should be done with great caution, taking into account sodium intake from the drinking water, which can be quite high during heat stress conditions. There is also an indication of beneficial effects of increasing the potassium levels in the diet, although again, this must be accomplished only after careful calculation, since high levels can be detrimental to electrolyte balance. While few reports indicate any improvement in adding supplemental B vitamins during heat stress, there are variable reports of the beneficial effects with the fat soluble vitamins. Although not always conclusive, increasing the levels of vitamins A, D3 and E have all been shown to be advantageous under certain conditions. While vitamin C (ascorbic acid) is not usually considered in poultry diets, there is evidence to support its use during hot weather conditions. Birds require vitamin C, but under most circumstances are able to synthesize enough in their own bodies. Under heat stress, such production may be inadequate and/or impaired. Adding up to 200 mg vitamin C/kg diet has proven beneficial for layers in terms of maintaining production.   
  &nbsp;  
  E.   Electrolyte Balance    
As environmental temperature increases, birds increase their respiration rate in an attempt to increase the rate of evaporative cooling. As birds pant however, they tend to lose proportionally more CO2 and so changes in acid-base balance can quickly develop. With mild through to severe alkalosis, blood pH may change from 7.2 through 7.5 to 7.7 in extreme situations. This change in blood pH, together with loss of bicarbonate ions can influence eggshell quality and general bird health and metabolism. Under such heat stress conditions, it is the availability of bicarbonate per se which seems to be the major factor influencing eggshell thickness, and in turn, this is governed by acid-base balance, kidney function and respiration rate.   
  Under normal conditions, shell formation induces a renal acidosis related to the total resorption of filtered bicarbonate. At the same time, shell secretion induces a metabolic acidosis because the formation of insoluble CaCO3 from HCO3 - and Ca++ involves the liberation of H+ ions. Such H+ release would induce very acidic and physiologically destructive conditions, and is necessarily balanced by the bicarbonate buffer system in the fluid of the uterus. While a mild metabolic acidosis is therefore normal during shell synthesis, a more severe situation leads to reduced shell production because of intense competition for HCO3 -, as either a buffer or a shell component. A severe metabolic acidosis can be induced by feeding products such as NH4C1, and this results in reduced shell strength. In this scenario, it is likely that NH4 + rather than C1 is problematic because formation of urea in the liver (from NH4 +) again needs to be buffered with HCO3 + ions, creating more competition with uterine bicarbonate metabolism. Conversely, feeding sodium bicarbonate, especially when C1 levels are minimized, may well improve shell thickness. Under commercial conditions, the need to produce base excess in order to buffer any diet electrolytes must be avoided. Likewise it is important that birds not be subjected to severe respiratory excess, as occurs at high temperatures, because this lowers blood bicarbonate levels, and in extreme cases, causes a metabolic acidosis. Under practical conditions, replacement of part of the supplemental dietary NaC1 with NaHCO3 may be beneficial for shell production.   
  Acclimatization to heat stress is a confounding factor, because temporary acute conditions are more problematic. For example, pullets grown to 31 weeks under constant 35 versus 21°C conditions exhibit little difference in pattern of plasma electrolytes. If birds are allowed to acclimatize to high environmental temperatures, there is little correlation between plasma electrolytes and shell quality. Temporary acute heat stress and cyclic temperature conditions seem most stressful to the bird.   
  Prevention of electrolyte imbalance should obviously be approached through incorporation of appropriate cations and anions in diet formulations. However it must be accepted that diet is only one factor influencing potential imbalance, and so general bird management and welfare also become of prime importance. Electrolyte balance is most usually accommodated by consideration of Na+KC1 balance in the diet, and under most dietary situations this seems a reasonable simplification. Electrolyte balance is usually expressed in terms of mEq of the various electrolytes, and for an individual electrolyte this is calculated as Mwt ÷ 1000. This unit is used on the basis that most minerals are present at a relatively low level in feeds. As an example calculation, the mEq for a diet containing 0.17% Na, 0.80%K and 0.22% C1 can be developed as follows:   

    
  A balance of around 250 mEq/kg is usual, and so for this diet there needs to be either an increase in Na or K level of the diet, or a decrease in C1 level.   
  Under practical conditions, electrolyte balance seems to be more problematic when chloride levels are high. On the other hand, use of NaHCO3 to replace NaC1, as is sometimes recommended during heat stress, can lead to a deficiency of chloride. Changes in diet electrolyte balance most commonly occur when there is a major change in ingredient usage, and especially when animal protein sources replace soybean meal and vice versa. Table 8 outlines electrolyte content and electrolyte balance of some major feed ingredients.         
  Within the cereals, electrolyte balance for milo is low, while wheat is high relative to corn. Major differences occur in the protein-rich ingredients, and relative to soy, all sources are low in electrolyte balance. As shown in Table 8, this situation develops due to the very high potassium content of soybean meal. Careful consideration to electrolyte balance must therefore be given when changes are made in protein sources used in formulation. For example, the overall balance for a diet containing 60% milo and 25% soy is 210 mEq/kg, while for a diet containing 75% milo and 10% fish meal the balance is only 75 mEq/kg. The milo-fish diet would perhaps need to be supplemented with NaHCO3.   
  Assuming that heat stress cannot be tempered by normal management techniques, then electrolyte manipulation of the diet may be beneficial. However, the technique should be different for immature birds compared to egg layers. With adult female birds, there is a need to maintain the bicarbonate buffer system as it relates to eggshell quality. As such, diet or water treatment with sodium bicarbonate may be beneficial again emphasizing the necessity to meet minimal chloride requirements. On the other hand, treatment of respiratory alkalosis in layers, with acidifiers such as NH4C1 while relieving respiratory distress, may well result in reduced shell quality. For immature pullets treatment with electrolytes is often beneficial and there is less need for caution related to bicarbonate buffering. Up to 0.3% dietary NH4C1 may improve the growth rate of heat stressed birds, although as detailed previously, it is not clear if this beneficial effect is via electrolyte balance/blood pH or simply via the indirect effect of stimulating water intake. Under commercial conditions, adding salt to the drinking water of young birds has been reported to alleviate bird distress and to stimulate growth.   
  &nbsp;  
  F.   Water     
A nutritional factor often overlooked during heat stress is the metabolism of water. It is well known that birds in hot environments drink more water, yet this has not been capitalized upon to any degree. It would seem logical to provide nutrients in the water, because water intake is increased at times when feed intake is depressed. Unfortunately, we have only met with very limited success to date with this type of management. What does seem more advantageous is to cool the water of laying hens. In studies with small numbers of birds, we have shown a distinct advantage to cooling the drinking water of birds housed in very warm environments. In a more large scale study in a commercial unit in California, Bell (personal communication) indicates improved feed intake and egg production in response to the cooling of water by just 5°C at an environmental temperature of 32°C (Table 9). Another factor to consider with water intake, is the possible effect of dissolved minerals and contaminants, etc., the effects of which may be greatly accentuated with increase drinking activity. In terms of mineral content, sodium concentration is the one most likely to cause problems.   
        

  G.   General Recommendations Concerning Heat Stress     
Under normal conditions, birds should be fed so as to attain optimum daily intakes of essential nutrients. Regardless of environment, the correct decisions cannot be made without knowledge gained from the monitoring of feed intake, body weight and egg weight. With heat stress situations (28- 40°C), the following points should be considered:   
  1. Never place underweight pullets in the laying house. They will always remain small with low feed intake and have little body fat reserve to sustain optimum egg production.   
  2. Increase the energy level of the diet (2850 Kcal ME/kg minimum) ideally by incorporation of fats or oils. Limit the use of fibrous ingredients if possible.   
  3. Reduce crude protein component (17% CP maximum) while maintaining daily intakes of methionine (360 mg) and lysine (720mg).   
  4. Increase mineral-vitamin premix in accord with anticipated change in feed intake. Maintain daily intakes of calcium (3.5g) and available phosphorus (400 mg).   
  5. Where shell quality is a problem, consider the incorporation of sodium bicarbonate. At this time, monitor total sodium intake, and ensure adequate chloride levels in the diet.   
  6. Use supplemental vitamin C (150 g/tonne) when heat stress occurs.   
  7. Increase the number of feedings per day and try to feed at cooler times of the day.   
  8. Keep drinking water as cool as possible. Analyze sodium content of water so as to calculate &quot;salt&quot; contribution from the water.   
  9. Use crumbled feed or large particle mash feed if available.   
  10. Do not make any diet changes when sudden short term (3 - 5 days) heat stress occurs.   
  
]]></description><pubDate>Thu, 22 Jul 2010 23:01:00 +0000</pubDate><link>http://www.poultrypro.com/poultry-articles/poultry-welfare/feeding-programs-for-laying-hens-heat-stress/</link><guid>http://www.poultrypro.com/poultry-articles/poultry-welfare/feeding-programs-for-laying-hens-heat-stress/</guid><author>Thu, 22 Jul 2010 23:01:00 +0000</author><comment></comment></item><item><title><![CDATA[Feeding Programs for Laying Hens: Phase Feeding]]></title><description><![CDATA[  Phase feeding refers essentially to reductions in the protein and amino acid level of the diet as the bird progresses through a laying cycle. The concept of phase feeding is based on the fact that as birds get older their feed intake increases, while their egg production decreases. For this reason, it should be economical to reduce the nutrient concentration of the diet. At this time, it is pertinent to consider a conventional egg production curve of a layer, and superimpose both egg weight and daily egg mass output (Figure 7). If nutrient density is to be reduced, this should not occur immediately after peak egg numbers, but rather after peak egg mass has been achieved. There are two reasons for reducing the level of dietary protein and amino acids during the latter stages of egg production namely, to reduce feed costs and secondly, to reduce egg size. The advantages of the first point are readily apparent if protein costs are high, but the advantages of the second point are not so easily defined and will vary depending upon the price of eggs. When a producer is being paid a premium for extra large and jumbo eggs, there is no advantage to using a phase feeding program unless egg shell quality is a problem.               
  It is difficult to give specific recommendations as to the decrease in dietary protein level that can be made to reduce egg size without decreasing the level of production. The appropriate reduction in protein level will depend on the season of the year (effect of temperature on feed consumption), age and production of the bird, and energy level of the diet. Hence, it is necessary that every flock be considered on an individual basis before a decision is made to reduce the level of dietary protein. As a guide, it is recommended that protein intake be reduced from 17g/day to 16g/day after the birds have dropped to 80% production, and to 15g/day after they have dropped to 70% production. With an average feed intake of 100 g/day, this would be equivalent to diets containing 17, 16 and 15% protein. It must be stressed that these values should be used only as a guide after all other factors have been properly considered. If a reduction in the level of protein is made and egg production drops, then the decrease in intake has been too severe and it should be immediately increased. If, on the other hand, production is held constant and egg size is not reduced then the decrease in protein intake has not been severe enough and it can be reduced still further. The amino acid to be considered in this exercise is methionine, since this is the amino acid that has the greatest effect on egg size. Phase feeding of phosphorus has also been recommended as a method of halting the decline in shell quality often seen with older birds. Using this technique, available phosphorus levels may be reduced from approximately 0.4% at peak production to slightly less than 0.3% at the end of lay. Table 10 shows an example of phase feeding of protein, methionine and phosphorus, related to egg production, and independent of feed intake.   
  A major criticism of phase feeding is that birds do not actually lay &quot;percentages&quot; of an egg. For example, if a flock of birds is producing at 75% production, does this mean that 100% of the flock is laying at 75% or is 75% of the flock laying at 100% production? If the latter is true, then the concept of phase feeding may be harmful. If a bird lays an egg on a specific day, it can be argued that its production is 100% for that day, and so its nutrient requirements are the same regardless of the age of bird. Alternatively, it can be argued that many of the nutrients in an egg, and especially the yolk, accumulate over a number of days, and so this concept of 100% production, regardless of age, is misleading.   
  Advocates of phase feeding indicate that birds can be successfully managed by reducing protein/amino acid contents of the diet-others suggest that nutrient specifications are too high to start with initially, and that phase feeding merely accomplishes normalization of diet in relation to requirement. The bottom line is that environmental and management conditions vary from flock to flock, and certainly from season to season within a flock. For this reason, the basis of phase feeding must be an accurate assessment of the nutrient intake relative to requirement for production, growth and maintenance.         
]]></description><pubDate>Thu, 22 Jul 2010 21:51:00 +0000</pubDate><link>http://www.poultrypro.com/poultry-articles/layers/feeding-programs-for-laying-hens-phase-feeding/</link><guid>http://www.poultrypro.com/poultry-articles/layers/feeding-programs-for-laying-hens-phase-feeding/</guid><author>Thu, 22 Jul 2010 21:51:00 +0000</author><comment></comment></item><item><title><![CDATA[Feeding Programs for Laying Hens: Nutrition and Shell Quality]]></title><description><![CDATA[         The laying diets shown in Table 1 contain all the calcium needed by the layer under most conditions. However, if egg shell quality is a problem during hot weather, or if the pullets have come into production at a fairly young age and have peaked very quickly, it may be advisable to increase the levels of calcium by at least 0.4%. Research has indicated that a marked improvement in shell quality can be obtained by feeding part of the dietary calcium as oyster shell or limestone chips. This is especially true if limestone flour rather than a granular source of limestone is used. The hen’s requirement for calcium is relatively low, except at the time of the day when egg shell formation is taking place. The greatest rate of shell deposition occurs in the dark phase, when birds are not actively eating feed. The source of calcium during this period then becomes residual feed in the digestive tract and the labile medullary bone reserve.   

  In the first six hours of the 24h laying cycle, there is virtually no shell deposition. This is the time of albumen and shell membrane secretion, and the time of redeposition of medullary bone. From six to 12 hours, about 400 mg calcium are deposited, while the most active period is the 12-18 hr period when around 800 mg shell calcium accumulates.   
  This is followed by a slower deposition of about 500 mg in the last six hours, for a total of around 1.7g shell calcium, depending upon egg size. The voluntary intake of oyster shell or large particle calcium at various times during a normal 16h day is shown in Figure 8.         
  With the control diet, the hen had no choice as to the time of day calcium was consumed. However, when given the simultaneous choice of diets providing energy, protein or calcium (E,P,Ca), the hen was able to select calcium at any time. Under these conditions, the hen consumed little or no calcium until the afternoon. This is the time of the day that the egg is usually in the shell gland, and the requirement for calcium should be higher at this time. When feeding limestone chips or oyster shell, it is recommended that the diet contain 1 to 1.5% calcium and that the remainder be supplied by the supplemental source. The ideal time to feed this calcium supplement would be in the afternoon, since this is when the hen normally has a high calcium requirement. Since separate feeding of calcium is not very practical, the only apparent solution is to have the calcium supplement mixed in the feed. The hen has the opportunity of leaving the oyster shell or limestone chips until the latter part of the day when it is required. This type of feeding method is being used by a number of producers with very good results. The feeding of limestone or oyster shell on a continuous free choice basis, or on top of a diet containing the full calcium requirement, is not recommended. It has been shown that egg shells with chalky deposits and rough ends are probably a direct result of feeding too much calcium to laying hens. Feeding birds oyster shell ad-libitum can also result in the production of soft shelled eggs. This unusual circumstance is due to a deficiency of phosphorus. If too much calcium is ingested, it must be excreted, usually as soluble calcium phosphate. This can lead to a deficiency of phosphorus, which results in no medullary bone being redeposited between successive periods of calcification.   
  Calcium is the nutrient most often considered when shell quality problems occur, although it is realized that deficiencies of vitamin D3 and phosphorus can also result in weaker shells. Vitamin D3 is required for normal calcium absorption, and so if inadequate levels are fed, induced calcium deficiency quickly occurs. Results from our laboratory suggest that diets devoid of synthetic vitamin D3 are quickly diagnosed, because there is a dramatic loss in shell weight (Figure 9). The same situation is seen in Figure 10 when birds are fed deficient diets, and shell quality quickly deteriorates over two to three weeks. In this study, the basal diet was resupplemented with vitamin D3 after four weeks, and there was rapid normalization of shell quality (Figure 10).               
  However, a more serious problem occurs with sub-optimal levels of vitamin D3, where changes in shell quality are more subtle but nevertheless of economic significance (Figure 10).   
  A major problem with deficiency of vitamin D3 is that this nutrient is very difficult to assay in complete feeds. If it is only at concentrations normally found in vitamin premixes that meaningful assays can be carried out, and so if D3 problems are suspected, access to the vitamin premix is usually essential. In addition to uncomplicated deficiencies of D3, problems can arise due to the effect of certain mycotoxins. Compounds such as zearalenone, that are produced by Fusarium molds, have been shown to effectively tie up vitamin D3, resulting in poor egg shell quality. Under these circumstances, dosing birds with 300 IU D3 per day for three consecutive days with water soluble D3 may be advantageous.   
  Minimizing phosphorus levels is also advantageous in maintaining shell quality, especially under heat stress conditions. Because phosphorus is a very expensive nutrient, high inclusion levels are not usually encountered, yet limiting these within the range of 0.3 to 0.4%, depending upon flock conditions, seems ideal in terms of shell quality. Periodically, unaccountable reductions in shell quality occur and it is possible that some of these may be related to nutrition. As an example, vanadium contamination of phosphates causes an unusual shell structure, and certain weed seeds such as those of the lathyrus species, cause major disruptions of the shell gland.   
  Up to 10% reduction in eggshell thickness has been reported for layers fed saline drinking water, and a doubling in incidence of total shell defects seen with water containing 250 mg salt/litre. If a laying hen consumes 100g feed and 200 ml water per day, then water at 250 mg salt/litre provides only 50 mg salt compared to intake from the feed of around 400 mg salt. The salt intake from saline water therefore seems minimal in relation to total intake, but nevertheless shell quality problems often occur under these conditions. It appears that saline water results in limiting the supply of bicarbonate irons to the shell gland, and that this is mediated via reduced activity of carbonic anhydrase enzyme in the mucosa of the shell gland. However it is still unclear why saline water has this effect, in the presence of overwhelmingly more salt as provided by the feed. There seems to be no effective method of correcting this loss of shell quality in established flocks, although for new flocks, the adverse effect can be greatly reduced by adding 1 g vitamin C/litre drinking water.   
  
]]></description><pubDate>Thu, 22 Jul 2010 21:42:00 +0000</pubDate><link>http://www.poultrypro.com/poultry-articles/layers/feeding-programs-for-laying-hens-nutrition-and-shell-quality/</link><guid>http://www.poultrypro.com/poultry-articles/layers/feeding-programs-for-laying-hens-nutrition-and-shell-quality/</guid><author>Thu, 22 Jul 2010 21:42:00 +0000</author><comment></comment></item></channel></rss>
