F Prelay nutrition and management

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i) Considerations for calcium metabolism -Prelay diets and prelay management are designed to allow the bird the opportunity to establish adequate medullary bone reserves that are neces sary for calcifying the first egg produced. In practice, there is considerable variation in formulation and time of using prelay diets, and to some extent this confusion relates to defining sexual maturity per se. Historically, prelay diets were fed from about 2 weeks prior to expected maturity, up to the time of 5% egg production. With early, rapid and hopefully synchronized maturation with today's strains, we rarely have the opportunity to feed for 2 weeks prior to maturity. Likewise, it is unwise to feed inadequate levels of calcium when flocks are at 5% production. One of the major management decisions today is the actual need for prelay diets, or whether pullets can sustain long-term shell quality when moved from grower diet directly to a high calcium layer diet.

The bird's skeleton contains around 1 g of medullary calcium that is available for shell calcification on any one day. This calcium is continually replenished between successive ovulations, and in times of inadequate calcium repletion, the medullary reserve may be maintained at the expense of structural cortical bone. Around 6070% of the medullary calcium reserves are located in the long bones, and so long-term problems of calcium deficiency can lead to lameness and cage layer fatigue.

Prelay diets normally contain 2-2.5% calcium, and when fed over a 10-14 d period provide the bird with the opportunity to deposit medullary bone. This bone deposition coincides with follicular maturation and is under the control of both estrogens and androgens. The latter hormone seems essential for medullary bone growth, and its presence is manifested in growth of the comb and wattles. Consequently, there will be little medullary deposition, regardless of diet calcium level, if the birds are not showing comb and wattle development and this stage of maturity should be the cue for increasing the bird's calcium intake.

Because egg production is an 'all or none' event, the production of the first egg obviously places a major strain on the bird's metabolism when it has to contend with a sudden 2 g loss of calcium from the body. Some of this calcium will come from the medullary bone, and so the need to establish this bone reserve prior to first egg. The heaviest pullets in a flock will likely be the first to mature, and so it is these birds that are most disadvantaged if calcium metabolism is inadequate. If these early maturing pullets receive a 1% calcium grower diet at the time they are producing their first few eggs, they will only have a sufficient calcium reserve to produce 2-3 eggs. At this time, they will likely stop laying, or less frequently continue to lay and exhibit cage layer fatigue. If these earlier maturing birds stop laying, they do so for 45 days, and then try to start the process again. The bird goes through very short clutches, when at this time she is capable of a very prolonged 30 - 40 egg first clutch. Advocates of prolonged feeding of grower diets suggest that it makes the bird more efficient in the utilization or absorption of calcium, such that when she is eventually changed to a layer diet, improved efficiency continues for some time, with the bird having more calcium available for shell synthesis. Figure 3.6 indicates that percentage calcium absorption from the diet does decline with an increased level of calcium in the diet.

  1. 3.6 Relationship between calcium intake and calcium retention.
  2. 3.6 Relationship between calcium intake and calcium retention.
Urolithiasis Broiler Breeders

However, with 40% retention of 5 g of calcium consumed daily, there will be greater absolute calcium retention (2 g/d) than the bird consuming 2.5 g Ca/d and exhibiting 60% efficiency of retention (1.5 g retained/d). There is also no evidence to support the suggestion of carry over of this higher efficiency during early egg production. If 1% calcium grower diets are used around the time of maturity, then these diets should not be used after the appearance of first egg, and to 0.5% production at the very latest. It must be remembered that under commercial conditions, it is very difficult to precisely schedule diet changes, and so decisions for diet change need to precede actual time of diet change, such that production does not reach 5 - 10% before birds physically receive the calcium enriched diets.

Prelay diets provide more calcium than do most grower diets, but still not enough Ca for sustained production. Prelay diets should allow the build up of medullary reserves without adversely influencing general mineral metabolism. However, as previously discussed for grower diets, 2 - 2.5% calcium prelay diets are inadequate for sustained egg production, and should not be fed beyond 1% egg production. The main disadvantage of prelay diets is that they are used for a short period of time, and many producers do not want the bother of handling an extra diet at the layer farm. There is also a reluctance by some producers with multi-age flocks, at one site, to use prelay diets where delivery of diets with 2% calcium to the wrong flock on site can have disastrous effects on production.

Simply in terms of calcium metabolism, the most effective management program is early introduction of the layer diet. Such high calcium diets allow sustained production of even the earliest maturing birds. As previously mentioned, higher calcium diets fed to immature birds, lead to reduced percentage retention, although absolute retention is increased (Table 3.33).

Feeding layer diets containing 3.5% calcium, prior to first egg, therefore results in a slight increase in calcium retention of about 0.16 g/d relative to birds fed 0.9% calcium grower diets at this time. Over a 10 d period, however, this increased accumulation is equivalent to the output in 1 egg. Since there is only about 1 g of mobile medullary calcium reserve in the mature bird, then the calcium retention values shown in Table 3.33 suggest accumulation of some cortical bone at this time.

Early introduction of layer diets is therefore an option for optimizing the calcium retention of the bird. However, there has been some criticism leveled at this practice. There is the argument that feeding excess calcium prior to lay imposes undue stress on the bird's kidneys, since this calcium is in excess of her immediate requirement and must be excreted. In the study detailed in Table 3.33, there is increased excreta calcium. However, kidney histology from these birds throughout early lay revealed no change due to prelay calcium feeding. Recent evidence suggests that pullets must be fed a layer diet from as early as 6 - 8 weeks of age before any adverse effect on kidney structure is seen (see following section on urolithiasis). It seems likely that the high levels of excreta calcium shown in Table 3.33 reflect fecal calcium, suggesting that excess calcium may not even be absorbed into the body, merely passing through the bird with the undigested feed. This is perhaps too simplistic a view, since there is other evidence to suggest that excess calcium may be absorbed by the immature bird at this time. Such evidence is seen in the increased water intake of birds fed layer diets prior to maturity (Figure 3.7).

Early introduction of a high calcium layer diet seems to result in increased water intake, and a resultant increase in excreta moisture. Unfortunately this increased water intake and wetter manure seems to persist throughout the laying cycle of the bird, (Table 3.34). These data suggest that birds fed high calcium layer diets during the prelay period will produce manure that contains 4 - 5% more moisture than birds fed 1% calcium grower or 2% calcium prelay diets. There are reports of this problem being most pronounced under heat stress conditions. A 4-5% increase in manure moisture may not be problematic under some conditions, although for those farms with a chronic history of wet layer manure, this effect may be enough to tip the balance and

Table 3.33 Effect of % diet calcium fed to birds immediately prior to lay on calcium retention

Diet Ca (%)

Daily Ca retention (g)

Excreta Ca (% dry matter)













3. 0






  1. 3.7 Effect of introducing a 4% calcium layer diet at 112 days (_) and at 138 (____) on daily water intake.
  2. 3.7 Effect of introducing a 4% calcium layer diet at 112 days (_) and at 138 (____) on daily water intake.
Table 3.34 Effect of prelay calcium level on excreta moisture (%)

Prelay diet Ca (%) (16 -19 weeks)1

Bird age (d)

























1 All birds fed 4.0% Ca after 20 weeks of age

1 All birds fed 4.0% Ca after 20 weeks of age produce a problem. The current trend of feeding even higher calcium levels to laying hens may accentuate this problem, and so dictate the need for prelay diets with more moderate levels of calcium.

In summary, the calcium metabolism of the earliest maturing birds in a flock should be the criterion for selection of calcium levels during the prelay period. Prolonged feeding of low-calcium diets is not recommended. Early introduction of layer diets is ideal, although where wet manure may be a problem, a 2% calcium prelay diet is recommended. There seems to be no problem with the use of 2% calcium prelay diets, as long as birds are consuming a high calcium layer diet no later than at 1% egg production.

ii) Prelay body weight and composition -Prelay diets are often formulated and used on the assumption that they will improve body weight and/or body composition, and so correct problems arising with the prior growing program. 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 in the live pullet. For this reason our main emphasis at this time is directed towards body weight.

Pullet body weight is the universal criterion used to assess growing program. 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 for most flocks, it is too late at this stage of rearing to meaningfully influence body weight.

However, if underweight birds are necessarily moved to a layer house, then there is perhaps a need to manipulate body weight prior to maturity. With black-out housing, this can some-times be achieved by delaying photostimulation - this option is becoming less useful in that both Leghorns and brown egg strains are maturing early without any light stimulation. If prelay diets are used in an attempt to correct rearing mismanagement, then it seems as though the bird is most responsive to energy. This fact fits in with the effect of estrogen on fat metabolism, and the significance of fat used for liver and ovary development at this time. While using high nutrient density prelay diets may have a minor effect 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 light weight and of small stature at say, 16 weeks of age, then the end result of using high nutrient dense prelay diets may well be pullets of correct body weight, but of small stature. Pullets with a short shank length seem more prone to prolapse/pick-out, and so this is another example of the limitations in the use of high nutrient dense prelay diets.

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 quantitate. There is no doubt that energy is likely the limiting nutrient for egg production of all strains of bird, and at peak egg numbers, feed may not be the sole source of energy. Labile fat reserves seem essential to augment feed sources that are inherently limited by low feed intake. 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 build fat reserves is greatly limited. Obviously, if labile fat reserves are to be of significance, then they must be deposited prior to maturity. As with most classes of bird, the fat content of the pullet can best be manipulated through changing the energy:protein balance of the diet. If labile fat reserves are thought necessary, then high energy, high fat prelay diets should be considered. As previously stated, this scenario could well be beneficial if peak production is to coincide with periods of high environmental temperature.

The requirement for a specific body composition at the onset of maturity has not been adequately established. With mammals, onset and function of normal estrus activity is dependent on attainment of a certain body fat content. In humans, for example, onset of puberty will not occur if body fat content is much less than 14%. No such clear cut relationship has emerged with egg layers. Work conducted with broiler breeders, in fact, indicates a more definite relationship between lean body mass and maturity, rather than fat content and maturity.

  1. Early egg size - Egg size is greatly influenced 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 mature body weight can also be applied to concerns with early 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 usual 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.
  2. Pre-pause - In some countries, and most notably Japan, pre-pause feeding programs are used to maximize early egg size. The idea behind these programs is to withdraw feed, or feed a very low nutrient dense diet at the time of sexual maturity. This somewhat unorthodox program is designed to 'pause' the normal maturation procedure, and at the same time to stimulate greater egg size when production resumes after about 10-14 days. This type of prelay program is therefore most beneficial where early small egg size is economically undesirable.

Pre-pause can be induced by simply withdrawing feed, usually at around 1% egg production. Under these conditions, pullets immediately lose weight, and fail to realize normal weight-for-age when refed. Egg production and feed intake normalize after about 4 weeks, although there is 1-1.5 g increase in egg size. Figure 3.8 shows the production response of Leghorn pullets fed only wheat bran from 18 weeks (or 1% egg production) through to 20 weeks of age.

Fig. 3.8 Early egg production of pullets fed wheat bran at 1% egg production or at 18 weeks of age.

17 18 19 20 21 22 23 27 31 35 39 43 47 Age (weeks)

Fig. 3.8 Early egg production of pullets fed wheat bran at 1% egg production or at 18 weeks of age.

The most noticeable effects resulting from use of a pre-pause diet such as wheat bran, are a very rapid attainment of peak egg production and an increase in egg size once refeeding commences. This management system could therefore be used to better synchronize onset of production (due to variance in body weight), to improve early egg size or to delay production for various management related decisions. The use of such pre-pause management will undoubtedly be affected by local economic considerations, and in particular the price of small vs. medium vs. large grade eggs.

v) Urolithiasis - Kidney dysfunction often leads to problems such as urolithiasis that some-times occurs during the late growing phase of the pullet or during early egg production. While infectious bronchitis can be a confounding factor, urolithiasis is most often induced by diet mineral imbalance in the late growing period. At postmortem, one kidney is often found to be enlarged and contain mineral deposits known as uroliths. Some outbreaks are correlated with a large increase in diet calcium and protein in layer vs. grower diets, coupled with the stress of physically moving pullets at this time, and being subjected to a change in the watering system (usually onto nipples in the laying cages). The uroliths are most often composed of calcium-sodium-urate.

The occurrence is always more severe when immature pullets are fed high calcium diets for an extended period prior to maturity. For example, urolithiasis causing 0.5% weekly mortality often occurs under experimental conditions when pullets are fed layer diets from 10-12 weeks of age (relative to maturity at 18-19 weeks). However, there is no indication that early introduction of a layer diet for just 2-3 weeks prior to maturity is a causative factor.

Because diet electrolytes can influence water balance and renal function, it is often assumed that electrolyte excess or deficiency may be predisposing factors in urolithiasis or gout. Because salts of uric acid are very insoluble, then the excretion of precipitated urate salts could serve as a water conservation mechanism, especially when cations are excreted during salt loading or when water is in short supply. When roosters are given saline water (1% NaCl) and fed high protein diets, uric acid excretion rates are doubled compared to birds offered the high protein diet along with non-saline drinking water. Because uric acid colloids are negatively charged, they attract cations such as Na, and so when these are in excess, there is an increased excretion via urates, presumably at the expense of conventional NH4 compounds. There is some evidence of an imbalance of Na+K:Cl levels influencing kidney function. When excess Na+K relative to Cl is fed, a small percentage of the birds develop urolithiasis. It is likely that such birds are excreting a more alkaline urine, a condition which encourages mineral precipitation and urate formation.

As previously described, Urolithiasis occurs more frequently in laying hens fed high levels of calcium well in advance of sexual maturity. Feeding prelay (2-2.5% Ca) or layer diets containing 4-5% calcium for 2-3 weeks prior to first egg is usually not problematic, and surprisingly, uroliths rarely form in adult male breeders fed high calcium diets. High levels of crude protein will increase plasma uric acid levels, and potentially provide conditions conducive to urate formation.

In humans, urolith formation (gout) can be controlled by adding urine acidifiers to the diet. Studies with pullets show similar advantages. Adding 1% NH4Cl to the diet results in a more acidified urine, and uroliths rarely form under these conditions. Unfortunately, this treatment results in increased water intake, and associated wet manure. One of the potential problems in using NH4Cl once the birds start laying is that the metabolic acidosis is detrimental to eggshell quality especially under conditions of heat stress. Such treatment also assumes the kidney can clear the increased load of H+, and for a damaged kidney, this may not always be possible. As a potential urine acidifier without such undesirable side effects, several researchers have studied the role of Alimet® a methionine analogue. In one study, pullets were fed diets containing 1 or 3% calcium with or without Alimet® from 5-17 weeks. Birds fed the 3% calcium diet excreted alkaline urine containing elevated calcium concentrations together with urolith formation and some kidney damage. Feeding Alimet® acidified the urine, but did not cause a general metabolic acidosis. Alimet® therefore reduced kidney damage and urolith formation without causing acidosis or increased water consumption. Urine acidification can therefore be used as a prevention or treatment of urolithiasis, and this can be accommodated without necessarily inducing a generalized metabolic acidosis. From a nutritional viewpoint, kidney dysfunction can be minimized by not oversupplying nutrients such as calcium, crude protein and electrolytes for too long a period prior to maturity.

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