Broiler Breeder Nutrition

Breeder nutrition is most often evaluated in terms of egg numbers and hatchability, with relatively scant regard to broiler performance. Within an integrated broiler operation, it is of course broiler growth characteristics that have the greatest impact on economics of poultry meat production, yet there is often disconnect between breeder and broiler nutrition. To some extent, this situation arises due to the physical separation of these operations, and the fact that there is invariably the intervening hatchery operation, which often is the scapegoat, when problems arise at the broiler farm. The nutrient profile of the breeder diet obviously influences the nutrient reserves for the embryo, in both the yolk and to a lesser extent the albumen. Because of the relatively short grow-out period of modern broiler chicks, the 0-7d starter period assumes an ever increasing proportional contribution to such growth. There is now concern about consistency of early chick growth, and the role of the breeder diet is often raised in such discussion. This paper reviews those aspects of broiler nutrition that may impact on early broiler growth and development. In recent years, there has been resurgence in interest regarding injecting late-developing embryos with an array of nutrients, again to influence early chick development. Breeder nutrition must be tailored to produce the greatest number of fertile eggs, and as such, judicious rationing of energy and protein is the usual criteria. The following discussion assumes that birds are being fed conventional diets in quantities that are similar to those recommended by the primary breeder. 

Immature pullets and roosters must be managed so as to achieve the desired uniform weight at the time of photostimulation, which is usually around 22 weeks of age. Growth and uniformity are influenced by feeding program and, to a lesser extent, by feed formulation. Within reason, it is possible to achieve the desired weight at any age when using diets with a vast range of nutrient specifications, since feed allocation is controlled. For example, it is theoretically possible to grow pullets on diets with energy levels ranging from 2,600 to 3,100 kcal ME/kg. In practice, diet energy level is usually within the range of 2,750-2,950 kcal ME/kg, although for diets necessarily formulated outside of this range, energy intake can be controlled by adjusting feed intake. It is usually more difficult to maintain uniformity with high-energy diets, since this necessarily involves much smaller quantities of feed being distributed at any one time, and so feed delivery time becomes the critical management factor.

Some type of physical feed restriction is universally used to control breeder growth. The traditional system has been skip-a-day, where, as its name implies, birds are fed only on alternate days. The skip-a-day feed intake will obviously depend upon nutrient density and environmental conditions. Because different strains of birds have different growth characteristics, the initiation of controlled and restricted feeding must be flexible in order to accommodate strain-specific growth potential. Feed restriction can start as early as 2 weeks or as late as 4 weeks depending on strain.

There is a trend away from skip-a-day towards everyday feeding since it is more efficient, and with superior management and supervision, better uniformity can be achieved. Improved efficiency results from birds utilizing feed directly each day, rather than there being the inherent inefficiency of skip-a-day-fed birds having to utilize stored energy for maintenance on the offfeed day. Most daily feed allowances are derived by using 50% of corresponding skip-a-day programs, but because of improved efficiency a 45% allowance is more appropriate, and hence the improved efficiency. Whatever system of feed restriction is used, the goals are to obtain a uniform and consistent growth rate through to maturity. Ideally, the pullets and roosters will be close to target weight by 16-18 weeks of age, since attempts at major manipulation in growth after this time often compromises body composition (birds get fatter), maturity and subsequent reproductive performance.

Roosters can be grown with the hens or grown separately, but in both situations, they will almost exclusively be fed starter and grower diets designed for the female birds. This poses no major problem because nutrient requirements of the sexes up to the time of maturity are similar. When males and females are grown together, the onset of restriction programs and feed allocation are usually dictated by progress in hen weight and condition. Male growth and condition cannot be controlled as well under these situations, and this has to be an accepted consequence of mixedsex growing systems. Growing roosters separately provides the best opportunity to dictate and control their development.

Water restriction is also important for juvenile breeders. With feed restriction, birds can consume their feed in 30 minutes to 2 hr and so given the opportunity, these birds will consume excessive quantities of water simply out of boredom or to satisfy physical hunger. Pullets given free access to water seem to have wetter litter, and there is no doubt that a water restriction program is necessary in order to maintain good litter quality and help prevent buildup of intestinal parasites and maintain foot pad condition. Water restriction becomes more challenging in hot weather.

There is considerable variation in application and use of prebreeder diets. While most primary breeding companies show specifications for prebreeder diets, it is common practice to change directly from grower diet to breeder diet. The prebreeder diet is really only useful as a transition diet in terms of calcium and high protein/lysine at this time can lead to excess breast muscle development. 

After 22 weeks of age, regardless of rearing program, all birds should be fed daily. Because energy intake is the major factor controlling egg production, then it is critical that feed intake be adjusted according to energy density of the diet. In general, most breeder flocks will be overfed protein because it is difficult to justify much more than 23-25 g of protein per day. Excess protein and amino acids contribute to muscle growth with birds becoming overweight. With a feed intake of 155 g daily, this means a protein need of only 15% of the diet. Peak feed is usually given anywhere from 30 to 60% egg production. If flocks are very uniform in weight, it is possible to peak feed at 30-40%. However, with poorer uniformity (<80% ± 15%), then peak allowance should not be given until 60% egg production or even later. Such so-called lead feeding programs are also influenced by management skills. Where there is good management with precise and an even feed distribution system, then peak feed can occur earlier than normal. Once birds have peaked in egg production, it is necessary to reduce feed intake. There is often confusion and concern as to how much and how quickly feed should be removed, and this is somewhat surprising, since the same basic rules used pre-peak also apply at this time. After peak production, feed clean-up time often starts to increase, and this is an indication of birds being overfed. The main problem we are trying to prevent at this time is obesity. If feed is not withdrawn after peak, then because egg production is declining, proportionally more feed will be used for growth. After peak, therefore, bodyweight becomes perhaps the most-important parameter used in manipulating feed allocation. It is still important for birds to gain some weight, since loss of weight is indicative of too severe a cutback in feed allocation. The higher the peak feed allowance the greater the amount of feed withdrawn and vice versa. For example with a peak allowance of 175g per day it will be necessary to remove up to about 25g by end of lay. With peak allowance of 150g, only about 8-10g can be withdrawn over time. Remember that the single largest factor impacting feed need is maintenance (at least 70% of intake) and that the major factors impacting maintenance are body weight and environmental temperature. The hens can be fed a single diet through the 40 weeks of production, or a diet with slightly lower nutrient density introduced midway through lay.

In the breeder facilities, there is the choice of using the breeder hen diet for all birds, or a separate diet specifically formulated for males. Such male diets will usually be much lower in crude protein, amino acids and calcium compared to the breeder hen diet. The protein and amino acid needs of the mature male are very low, being in the range of 10% crude protein. Such low-protein diets are often difficult and expensive to formulate per unit of nutrients supplied, but do allow for greater control of bodyweight and consequently fertility will usually be improved. A practical compromise is to formulate diets at around 12% crude protein or to use a 14-15% pullet grower diet. The calcium present in the hen breeder diet is also excessively high for the male. Because it is not producing eggshells, the male needs only 0.7-0.8% calcium in the diet. 

Chick size is usually 60-70% of initial egg weight, depending upon the time chicks are weighed in relation to hatch time. It is expected that chick weight will increase as breeders get older. As hatching egg size increases from 50g to 70g, and assuming a 64% chick yield per egg, chick size can be expected to increase from 32g with young flocks to almost 45g from flocks at the end of the cycle. The age related increase in egg size is a consequence of increases in weight of both albumen and yolk. The yolk exhibits the largest proportional increase, since it represents only about 25% of egg mass in young breeders and 32% in older birds. Even though there is an actual increase in albumen weight, from 30→40g over this same period, proportional yield declines from 64% to 58% in eggs from older breeders. Interestingly therefore, there is about a 10g increase in actual weight of both yolk and albumen as egg size increases from 47 to 69g. It is this 20g of additional nutrients that allows for the larger chick size from older breeders.

Apparently, not all of these additional nutrients are immediately utilized by the chick, since as breeder age increases, chicks tend to have larger residual yolks in their abdomen. Although this unabsorbed yolk contributes to chick size per se, it may not always be used for growth. When there is a ready supply of feed and water, the residual yolk is often not fully utilized. It is only in situations of delayed placement that the yolk is almost fully depleted, representing a valuable source of energy and water from breakdown of fats and protein. Chicks from older breeders therefore tend to withstand delayed placement better than do chicks from younger breeders, because they become less dehydrated. Chicks from young breeders lose at least an extra 1% of body weight when they are held in boxes at the hatchery for 24 hr prior to placement. 

The effects of breeder age on broiler growth rate are not always easy to interpret, and this may be the reason for variable conclusions. An obvious confounding situation is season, since we are studying information over a 40-week period. For breeders maturing in June in the Southern Hemisphere, broilers hatched from the mid-part of the cycle are more likely to be subjected to heat-stress conditions, and so this may temper growth rate. In commercial situations there may also be subtle changes in feed composition, and health status of breeders may change throughout their breeding cycle. It is also impossible to replicate hatches. The most reliable information therefore comes from breeders housed in 'controlled environmental' facilities where they are fed a diet composed of a single batch of ingredients. Even under these conditions, the best we can do is to observe trends over time. We recently conducted such a study in which management conditions were as standardized as possible for both breeders and their broiler offspring. Hatches were conducted when breeders were 28, 38, 48 and 58 weeks of age, and broilers from the last 2 hatches were grown under slightly warmer conditions than broilers from the first 2 hatches. If egg size/chick size is going to influence broiler growth, one expects this to manifest as better early growth. When broilers were weighed at 18 d of age, there was no relationship between egg/chick size and broiler weight. In fact, 18 d male and female broilers from 58 week old breeders were smaller than comparably aged birds from 28 week breeders even though the former were some 5 g heavier at hatch. However when broilers reached 49 d, there was improved growth with increased breeder age (Table 1).

Table 1. 49 d broiler growth characteristics as affected by breeder age

Although data is not always statistically significant, regression analyses shows a very high correlation for both live weight and carcass weight relative to breeder age and egg weight. Table 2 shows the average change in live weight and carcass weight for 49 d male and female broilers expressed per 1 g change in breeder egg weight.

Table 2. Change in production characteristics per 1 g increase in breeder egg weight.

It must be remembered that the performance increases shown in Table 2 refer to the age-related increase in egg size. It is not known if these data can be applied to differences in egg size within a given hatch, independent of breeder age. The improvement in live weight is greatest for female broilers, but for both males and females the increased live weight per gram of egg size is less than our previous estimate of 10 g/g egg size. The unit increases in carcass weight are much higher than expected relative to the improvement seen in live weight. The greater breeder agerelated effect on carcass weight suggests improved carcass yield independent of any increase in live weight. 

Breeder nutrition and feeding is always challenging because of the diverse options available to achieve the same goal. Optimum breeder performance is not always most economical for an integrated company, since it is broiler performance that has most impact on overall profitability. For example "overfeeding" breeders causes reduced egg production and chick yield, although chicks and broilers will be larger. Breeder nutrition and feeding strategy need to be tailored to the overall goals of the company.