Nutritional Requirements of Modern Laying Hens
The ability of nutritionists to formulate feed to provide nutrient levels for optimum economic layer performance is dependent upon understanding the microenvironment in which layers are reared, and upon adjusting feed formulations for those changes in feed intake caused by the environment. The environmental temperature has a tremendous influence on feed consumption, because the layers try to maintain a homeostatic body temperature by adjusting the intake of nutrients to the amount of heat the laying hen dissipates. The dietary requirements for ME and amino acids for layers should be based on specific environmental conditions, maintenance needs and product output. The maintenance energy requirement for layers is very dependent on environmental temperature and body size and has a tremendous effect on total daily feed intake.
It has been said that the commercial egg-type laying hen “lays eggs with its beak”. In other words, it is essential that the layer consume adequate nutrients and energy each day if she is expected to perform at her full genetic potential. Many times the hen’s performance is limited by inadequate nutrition. The hens will use the nutrients and energy for maintenance, general activity, egg production, size and growth. The size of the hen will influence the amount of feed she consumes. Layers of a light strain will normally consume less feed than a heavier strain. However, both light and heavier strains are very capable of high production. Environmental temperature is known to influence feed intake. Feeding adjustments can help to overcome some of the production drops, which occur in layer flocks due to increased environmental temperature. Feed adjustments are not the only solution, and some management practices will also contribute to alleviate the problem.
Warmer environmental temperatures that lower feed intake and energy requirements of layers may be economically beneficial if the temperatures registered at the farm are not extreme and the nutrient concentration of the feed is increased to compensate the decreased feed intake.
In recent years, the Management Guides for the Commercial layer edited by the Breeder Companies, have recommended substantial dietary increments in protein, amino acids, calcium, phosphorus and energy to allow maximum performance. Higher levels of protein and amino acids have also been encouraged in modern feed formulas because of their stimulus to egg size. The daily amino acid requirements for layers are primarily affected by egg mass output with a small percentage of daily needs used for maintenance. The increase in dietary protein levels in feed formulas is usually from feedstuffs with a lower metabolizable energy, thus nutritionists have been forced to add fat to keep dietary energy levels equal to the past. Being the quality of the energy utilized as important as the quality of the protein itself, the use of FFSBM represents a unique opportunity to supply both nutrients.
The continuing trend of Commercial Breeders to produce genetic stock with combined lower expected feed intake and genetic potential for increased egg mass production will require nutritionists to truly understand the importance of specific nutrients and also know the amount of nutrients needed for specific functions. The present laying hen utilized by the industry has been genetically selected to initiate lay at an earlier age, produce more egg mass, and consume less feed than the layers of the past.
Temperature And Dietary Energy Levels On Layer Performance As mentioned before, temperature has a direct influence on feed consumption and total energy intake. Egg mass is consequently affected by both very low and high temperatures. In general terms, body weight is increased by feeding high energy diets, and body weight gain is decreased as temperature increases.
Whenever layers are housed in hot climates, feed intake is lower than when they are housed in cooler climates. The decrease in feed intake will, in many instances, cause problems in the performance of the flock. Feed consumption is lower due to the reduced daily energy that the hens require for maintenance. In other words, the higher environmental temperature reduces the daily energy need of the hen for maintaining her body temperature due to her body temperature being closer to environmental temperature. Less heat is being dissipated from her body to the environment due to the narrow temperature gradient between her body temperature and the environmental temperature. Body weight gain is not as great in hot weather, total egg production and egg size are depressed and egg shell quality problems are usually present, especially after 40 weeks of age. Therefore, the major concern in hot weather is the decreased nutrient and energy intake of the flock to sustain egg production, egg weight and shell quality.
Two main options are available to increase energy consumption in hot weather. Feed intake can be stimulated and/or more energy can be added to the diet by increasing the caloric density of the feed. Several methods exist in order to achieve the first option, like flushing water lines several times a day, increasing the number of feedings per day from 3 to 4, to 6 or 7 times each day.
The second option is to increase the energy content of the diet. To accomplish this, the use of supplemental fat needs to be considered. Fat will not only add more energy to the diet, but will provide an “extra caloric” effect in hot weather. Dietary fat will improve the palatability of the feed. The laying hen and other poultry will usually adjust their feed intake according to the energy content of the diet. When the energy content is high, the bird consumes less feed and vice versa. However, this adjustment mechanism seems less perfect at higher environmental temperatures. Therefore, the bird may slightly over consume on calories in hot weather for a short period of time when higher dietary energy levels are used. Thus would be especially true when supplemental fat is added to the diet. Again, fullfat soybeans are very useful in hot weather.
In an experiment run by Zollitsch et al., in 1996, Dekalb layers housed at 30.5°C had the advantage of a lower maintenance requirement, because of the warm temperature, and although the hens consumed significantly less feed from this environment, the hens were able to consume enough feed to produce near maximum output of egg mass. In this same feeding trial, the overall optimum environmental temperature and dietary energy level for maximum feed efficiency and egg mass production was set at 30.5°C and 2976 Kcal ME/kg.
According to the Hy-line Brown Layer Management Guide the energy requirement for a layer under a moderate environmental temperature can be calculated using the following equation:
Kcal/bird/day = W (140 – 2T) + 2E + 5 ^^ W
W = current body weight in kilograms
T = Average environmental temperature in Celsius degrees.
E = Daily egg mass in gr/bird/day (% production x egg weight in gr) / 100
^^ W = Increment in body weight in gr/bird/day
The daily energy consumption can de determined as follows:
Kcal/kg of feed x g/bird/day by 1000 = Kcal/bird/day
In the same way, the amount of calories in feed can be calculated to reach a daily consumption determined following the next equation:
Kcal/kg of feed = Kcal/bird/day (desired) x 1000 / g/bird/day (actual)
They recommend relatively high energy levels when the total consumption of energy is a restrictive factor. This includes critical periods between housing and maximum production. Lots with an energy consumption below 285 Kcal/bird/day during the laying period tend to suffer egg production reductions and the egg size is also reduced. Again, heat stress will also result in a low feed and energy consumption. Increasing nutrient density, including energy (a moderate amount of fat) will contribute to maintain production yield and egg size when the environmental temperatures are high.
Again, fat is a concentrated energy source that can be used to increase the energy content in feed. Vegetable fat has the additional advantage of producing relatively low body heat increments, which is useful during periods of heat stress. Soybean oil has a high content of linoleic acid, which contributes to increase egg size.
The following chart is a guide to add fat to the feed according to different ages and environmental temperatures. Upon the addition of fat to the ration, the nutritionist should be careful of adding other nutrients in proportion to the energy.
Added Fat (%)
If a country does not pay a premium for egg size, then the most efficient system would be to provide layers with a warmer environment to lower maintenance requirements and keep nutrient intake adequate for maximum egg output without feeding additional nutrients for extra egg size.
The Effect Of Adding Dietary Fat To Increase Egg Mass Response With Total Sulfur Amino Acid Levels
In general terms, it has been observed that the addition of sulfur amino acids (methionine from 650 – 750 mg) has no effect on egg production, egg mass or egg weight, unless accompanied with the addition of fat ranging from 2 to 4%. The addition of higher levels of TSAA seems to be related to an increment in the weight of the yolks, while the increment in the concentration of ME seems to be related to an increment in the number of eggs produced. However, ME is also related to the production of a larger egg mass as we can see when a higher level of TSAA is utilized. Werner et al., report that the percentage of egg yolk from hens fed diets containing 2900 and 3050 kcal ME/kg was higher than the percentage of yolk in those eggs from hens fed from 2450 to 2600 kcal ME/kg .
When layers are severely energy deficient, the addition of energy will first show a large increase in egg numbers (egg weight may actually decrease), and then as the energy requirements for egg numbers are obtained, the hen partitions more to egg weight.
Feeding Optimum Levels Of Protein And Essential Amino Acids For Layers
The development of an ideal protein and amino acid profile for layers is needed to minimize layer nitrogen waste, potentially improve performance in hot temperatures with less heat increment, and increase the economic return of dietary protein and amino acids by improving the amino acid efficiency of utilization. A key problem associated with the validity of an “ideal protein concept” for layers is that past research has indicated layers need protein per se (Penz and Jensen, 1990) for producing larger egg albumen weights and total egg weights. At the same time covering a minimum level of total lysine and digestible lysine in the ration is directly related to an optimum feed conversion and thus optimum egg mass production by the layers (Rostagno, 2002).
Summers et al., (1990) reported that layers fed a 10% protein diet supplemented with methionine, lysine, tryptophan, and arginine produced 11% less egg mass compared to layers fed 17% protein diets. A few years later Harms and Ivey (1993) suggested the order of limiting amino acids for layers fed corn-soybean diets is methionine, lysine, tryptophan, arginine, and valine.
The egg composition and performance of layers fed corn – soy – meat and bone 14% CP diets with added methionine, lysine, isoleucine, and valine is equal to layers fed 18% CP control diets. The research has shown that the different commercial layer strains fed 14% protein diets with added amino acids to provide an ideal protein, perform equal to layers fed higher protein diets. Nitrogen loss in excreta is about 15 percent less for layers fed 14% protein diets supplemented with amino acids compared to layers fed 18% protein diets. The order of limiting amino acids in a 14% CP corn-soymeat and bone diet is methionine, TSAA, isoleucine, valine, lysine, arginine, threonine, and tryptophan. It takes approximately a 16% CP diet consisting of corn-soy-meat and bone meal to provide the correct levels of digestible isoleucine, and valine for a hen consuming 100 grams of feed daily.
Presently, it is not economical to add synthetic isoleucine or valine to poultry diets. (Coon, 2001). Most layer management guides suggest a 16% CP diet from 50% laying rate to reach maximum production (32 weeks) and from 32 to 44 weeks of age, except for Hy-line Brown and Lohmann who recommend an average of 18 % CP. However, for the ideal protein concept to be adequately applied, the level of lysine is to be taken as a sound reference to estimate the requirements for the rest of the essential amino acids. In addition to this feed consumption, as determined by strain and climatic conditions (mainly temperature and humidity), will influence the total energy consumption, and based on this, the final protein, lysine and the other amino acid concentrations are to be set for a maximum layer performance (Rostagno, 2002). Feeding imbalanced diets with regard to protein and amino acids will result in increased amino acid catabolism and thus in increased heat production.
Calcium Requirements In Laying Hens
The last NRC publication (NRC, 9th Edition, 1994) suggested the calcium requirement was only 3.25% for 100 gram intake, however, the committee stated that the requirement might need to be higher for maximum egg shell thickness. The continuing recommended increase in dietary calcium for layers is probably justified because of an overall increased shell mass production during the laying cycle.
The different forms of dietary calcium and the large range in particle size utilized in previous layer studies may have been partially responsible for the variations in response to calcium. Coon determined in a recent study that the optimum solubility range for limestone is between 11 and 14%. This solubility value can be obtained by mixing the right portion of limestones of various sizes.
Since bone calcium will be mobilized to support dietary calcium levels during egg shell formation, nutritionists need to feed a level of dietary calcium that will not deplete all bone reserves of calcium during the complete laying cycle. Research indicates that feeding optimum calcium levels and the correct limestone solubility to young layers and then continuing with this system during the entire laying period will help support stronger bones and egg shells at the end of the entire laying cycle.
To maximize egg shell quality and maintain strong bones, older layers at the end of a laying cycle may need a lower soluble limestone (8 to 10%) and a higher calcium intake (5 gr. for eggs shells and 6 gr. for bones).
Vitamins And Minerals In Feed Under Heat Stress Conditions
In order to maintain the consumption of adequate daily quantities of minerals and vitamins when feed intake decreases, their percentage in the diet should be increased. Sometimes adding large particle limestone and oyster shell with the proper solubility to the top of the feed is beneficial in maintaining calcium consumption in hot weather. Research has shown that hot weather does not have an effect on calcium source solubility in the hen’s digestive tract. The calcium sources with lower solubility in the digestive tract will be retained longer in the tract and the calcium will be available during the night when the egg shell is being formed. This is why midnight feeding and feeding calcium sources of lower solubility are associated with improved egg shell quality.
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