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.
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.
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.
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.
Diet and Egg Size
Increasing the hen’s intake of balanced protein will result in an increase in egg size while feeding higher levels of protein at the onset of production may help to increase egg size more rapidly. For strains of birds that produce many extra large eggs during the latter part of their egg production cycle, lowering the level of dietary protein during this period will result in slightly smaller and more uniform eggs.