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 "requirement". Certainly higher-energy diets do fool the bird into eating more energy, but the response is small, and "over consumption" 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 "ideal" 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 "mean" 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.Layers