Pre-Breeder Diets

Table of Contents

1. Introduction
2. The Pre-Breeder Period
3. Conclusions

Introduction

While most breeding companies provide nutrient specifications for pre-breeder diets, there is considerable variation in their commercial use and application. Using a pre-breeder or pre-lay diet is based on the assumption that the birds nutrient requirements change in this critical period of the birds life. There are certainly major changes occurring in the birds metabolism, hopefully related to ovary and oviduct development, and so this is the basis for a specialized diet at this time. With egg-laying stock, pre-lay diets most often involve a change in calcium nutrition, in order to establish the birds calcium reserves necessary for rapid and sudden onset of eggshell production. The same situation can be applied to heavy breeders today, because with flocks of uniform body weight and with good light management, the subsequent synchronization of maturity leads to rapid increase in egg numbers up to peak production. However, most often pre-breeder diets are used in an attempt to "condition" or correct growth and/or body compositional problems that have arisen during the 14-18 week growing period. In these situations managers are perhaps ill-informed of the expectations of merely changing diet specifications at this time.

The Pre-Breeder Period

Although there is no specific pre-breeder "period", most consider the 19-23 week period to be the major transition time for sexual development of the bird. During this time (4 weeks) the pullet is expected to increase in weight by about 570 g. This is somewhat more than the growth expectation of around 340 g for the previous 4 weeks (15-19 week) or growth of around 470 g for the 4 weeks from 23-27 weeks of age. It is expected that a significant proportion of this growth spurt will be as ovary and oviduct, which are developing in response to light stimulation. A practical complication of this expected development, is that it invariably coincides with move of the pullets from grower to breeder facilities. Under adverse conditions, such as transportation over long distances, heat stress, etc., then birds can lose up to 100 g of body weight at this critical time. If weight loss is characteristic of such transportation, then pullets should be given an extra feeding. For example, pullets should be moved on an "off-feed" day, but be fed that day in the breeder house after all birds are housed. We cannot allow weight loss at this critical time, and so the question to be answered is - do pre-breeder diets help in this physical move, as well as prime the bird for sexual maturity? Development of the ovary and oviduct require both protein/amino acids and energy (fat) accretion. Nutrients of interest, therefore, are protein and energy, together with increase in calcium for early deposition of medullary bone. However it has never been clearly established that such nutrients need to come from a specially fortified diet versus simply increasing the feed allowance of the grower diet or breeder diet that is introduced prior to maturity.

Following are factors to consider in feeding the bird in the pre-breeder transition period.

Calcium Metabolism

With egg-layers, pre-lay diets are used essentially to pre-condition the pullet for impending eggshell production. The very first egg represents a 1.5-2.0g loss in calcium from the body, the source of which is both feed and medullary bone reserve. Today breeder hens are capable of a sustained long clutch length which is necessary to achieve the 85-87% peak production that is now readily attainable. Calcium metabolism is, therefore, very important for the breeder. With Leghorn hens the consequence of inadequate early calcium balance is cage layer fatigue. Breeders do not show such signs, because they naturally have more exercise, and also have a readily available rich source of diet calcium in the form of their flockmates eggs. Hens have an innate ability to select out calcium, and so improperly fed breeders will eat litter and eggshells in an attempt to balance their diet. However inadequate calcium in the diet does lead to disruption of ovulation, and so these birds stop laying until their meagre calcium reserves are replenished. In a breeder flock, it is the larger bodied, early maturing pullets that are disadvantaged in this manner.

Commercially, we see three different approaches used in pre-breeder calcium nutrition. Firstly, is the use of grower diets that contain just 0.9 - 1.0% calcium being fed up to 5% egg production. This is the system that was used many years ago, and unfortunately is still sometimes used today. At 5% egg production, we do not have 100% of the flock producing at 5% egg production - rather we have closer to 5% of the early maturing pullets producing at close to 100% production. Pullets can produce just 2-3 eggs with a diet containing 1% calcium. After this time they will eat litter/eggs as previously described, or more commonly simply shut down the ovary. With this approach, birds may in fact be at 10-15% production before the breeder diet is introduced, because no farm system allows for instantaneous change in feed supply as feed tanks are hopefully never completely empty. There is no justification, therefore, for this old system of feed management, because it will be very detrimental to life-time productivity of today's genetic stocks.

The second system involves the classical pre-breeder diet containing around 2% calcium, which is really a compromise situation. It allows for greater medullary bone reserves to develop, without having to resort to the 3.5% calcium as used in a breeder diet. However 2% calcium is still inadequate for sustained eggshell production - with this diet the breeder can produce 4-6 eggs before ovulation pattern is affected. If a pre-breeder diet is used, therefore, and a moderate calcium level is part of this program, then the diet must be replaced by the breeder diet before egg production starts. A good rule of thumb is to change from pre-breeder to breeder when the very first egg is noticed, because this occurs usually around 10 days before 1% egg production.

The third option is perhaps the most simple solution, and involves changing from grower to breeder at 1st egg (10 days before 1% production). Having the breeder diet in place before maturity, ensures that even the earliest maturing birds have adequate calcium for sustained early egg production. Proponents of pre-breeder diets suggest that breeder diets introduced ealry provide too much calcium, and that this contributes to kidney disorders, because the extra ingested calcium must be excreted in the urine. There is an indication with Leghorns that feeding adult layer diets for 10-12 weeks prior to maturity can adversely affect kidney function, especially if birds are also challenged with infectious bronchitis. However feeding "extra" calcium for one or two weeks prior to maturity has no such effect. It is also interesting to realize that most roosters today are fed high-calcium breeder diets, which provide 4-6x their calcium needs, yet kidney dysfunction is quite rare in these birds.

Body weight and size

Body weight and body condition of the bird around the time of maturity, are perhaps the most important criteria that will ultimately influence breeder performance. 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. 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, prelay diets should not be used in an attempt to manipulate mature body size. The reason for this is that with most flocks it is too late at this stage of rearing to meaningfully influence body weight - all too often prelay diets are used as a crutch for poor rearing management.

However, if birds are underweight when placed in the breeder house, then there is perhaps a need to manipulate body weight prior to maturity. Under controlled environment conditions, this can sometimes be achieved by delaying photostimulation. If prelay diets are then necessarily used in an attempt to correct rearing mismanagement 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 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 say, 16-18 weeks of age, the end result of using high-nutrient dense prelay diets may well be pullets of correct body weight, but of small stature. These short-shank length pullets seem more prone to prolapse/pick-out, and so this is another example of the limitations in use of classical pre-lay diets.

Use of high-nutrient dense prelay diets to manipulate late growth of broiler breeder pullets does, however, seem somewhat redundant. The reason for this is that with restricted feeding programs, it is more logical to increase feed allowance than to add the complexity of introducing another diet. The only potential problem of this program is that in extreme cases feed intake is increased to a level that is in excess of the initial allowance of breeder diet at start of lay ie. ensure that breeders are not subjected to a step-down in feed allocation at time of first egg.

Body composition

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 measure. There is little doubt that energy is likely the limiting nutrient for egg production for all classes of birds, and that around peak production, feed may not be the sole source of such energy. Labile fat reserves at this time are, therefore, essential to augment feed sources. 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.

Egg weight and hatchability

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. 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 regular 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 prelay diets.

For breeders we must also consider egg composition as it relates to early hatchability success. Eggs from young breeders seem to inherently have a hatchability problem, and perhaps this is one of the reasons that we wait for egg size to increase before sending eggs to the hatchery. The reason for this early hatch problem is not fully resolved, but most likely relates in some way to maturity and development of embryonic membranes and their effect on transfer of nutrients from the yolk to the embryo. However part of this problem may also elate to inadequate transfer of vitamins into the egg. For a number of critical B-vitamins, their concentration in successive eggs does not plateau until after 7-10 eggs have been laid. The effect of pre-lay nutrition on these factors probably warrants further study, but at this time these problems cannot be resolved by simply over-fortifying prebreeder diets with vitamins or certain fatty acids.

Conclusions

Pre-breeder diets can successfully be used as part of a feeding program aimed at maximizing production potential in young breeders. However any desired increase in nutrient intake prior to maturity can most easily be achieved by simply increasing the feed allowance of either grower or adult breeder diet at this time. If pre-breeder diets are used, then 19-23 weeks seems the most ideal time, assuming 1% production will occur around 24 weeks of age.