Broiler Breeder Nutrition and Management (Part I)

Genetics, Nutrition And Reproduction
Poultry breeding remains largely based on classical quantitative genetics. In essence, pedigree broiler candidates are full-fed nutritionally-dense and properly balanced diets to allow individuals that have the greatest potential to utilize crude protein (CP) and metabolizable energy (ME) to grow fast, convert feed efficiently, and yield well to become apparent by their performance. Thus, broiler strains are often selected on high-protein, high-energy diets. Selection on nutrient dense diets apparently necessitates nutrient-dense diets in order for the progeny to fully express their genetic potential. An excellent example of the relationship between genetic progress and appropriate nutritional compensations can be taken from research with quail (Lilburn et al., 1992). Random-bred Japanese quail were placed on a selection program intended to create heavy weight (HW) quail. These quail were full-fed 28% CP diets for 28 days and then the largest birds were selected and mated to produce the next generation. When these birds were reared to sexual maturity on a 24% CP diet, as recommended by the National Research Council (NRC, 1984), there was an obvious delay in sexual maturity (onset of egg production).

When the HW quail and the non-selected randombred control (RBC) quail were fed a range of diets differing in % CP from hatch to sexual maturity a nutritional-genetic interaction became evident. The RBC quail, when fed the NRC recommended 24% CP diet from hatch, matured sexually at about 42 days of age. In contrast, the HW quail exhibited delayed sexual maturity on the same diet. However, when the HW quail were fed a 30% CP diet, more like that fed during their pedigree selection process, the delay in sexual maturity was noticeably reduced (Figure 1). These data make the strong suggestion that declining reproductive function due to genetic selection for non-reproductive traits may in some way be ameliorated nutritionally.

Interaction Of Nutrition, Temperature And Lighting Program
The very important interaction between climate, photostimulation, and nutrition can be illustrated by examining the seasonality of broiler breeder reproduction in temperate climates. The differences in so-called "in-season" and "out-of-season" breeders have historically been attributed to daylength. However, the interaction between daylength and seasonal differences in temperature and feed intake provide an alternative explanation of seasonality. In-season breeders are generally the better performing birds in a temperate climate. These birds typically hatch in warm periods of the year when daylengths are long. Daylength and temperature both decline during the rearing period. As broiler breeders have typically been fed to achieve a body weight standard, the cool weather at the end of the rearing period dictates more feed be fed. Thus, the cumulative nutrition is adequate for in-season breeders if photostimulation is not too early. In contrast, out-of-season birds hatch in the cool season and are reared while both daylength and temperatures are increasing. As the birds approach the age of photostimulation in warmer temperatures, they require less feed to achieve the standard body weight and thus have less cumulative nutrition at the point of photostimulation. This causes a delay in onset of egg production and is frequently the case for tropical countries. Many managers respond to this with earlier photostimulation, but this often does not correct the problem. Increasing the target body weight has often been used as a "treatment" for out-of-season (hot temperature grown) birds because, as we now know, having a heavier body weight effectively increases the cumulative nutrition in the warmer weather (see discussion below).

Another method of correcting delayed onset of egg production in warm weather has been to delay photostimulation until sufficient cumulative nutrition has been achieved. With this latter approach, body weight will not become excessive, but this approach may not work as well as increasing the cumulative nutrient intake to 20 weeks of age. If the current genetic trend toward improved feed efficiency continues, breeders will have to be photostimulated much later and/or grown to a higher body weight at 20 weeks of age in order to accumulate sufficient nutrition for proper responsiveness to photostimulation.

At this point, it should be stated that photostimulation plays a major role in the overall process of nutrient accumulation. Photostimulation somehow changes the birds from a "nutrient-accumulating" to a "nutrient-expending" organism. This is the probable reason that age at photostimulation has been delayed with good results in modern feed-efficient lines of broiler breeders. An extended rearing period is needed for some birds to accumulate sufficient nutrition for optimum reproduction. As shown below, this is certainly true for females (Walsh, 1996; Walsh and Brake, 1997; 1999) and one can interpret the large body of French literature to mean the same for males (de Reviers, 1977; de Reviers, 1980; de Reviers and Williams, 1984; de Reviers and Seigneurin, 1990). In these male data, most heavy-line male fertility problems could be avoided by simply not photostimulating the birds and thus giving them unlimited time to accumulate sufficient nutrients necessary to sustain optimum reproduction before actually achieving sexual maturity. The act of photostimulation can obviously interrupt the process of nutrient accumulation.

The Concept Of Minimum Cumulative Nutrition
During recent years, our laboratory has examined the relationship between cumulative nutrition during the rearing period and subsequent female reproductive performance. The rearing period was defined as the time from placement at one day of age to photostimulation at 20 weeks of age. Four groups of broiler breeders of the same strain are compared in Table 1 (Peak and Brake, 1994).

Photostimulation was at 141 days of age. Table 1 shows the cumulative CP, ME, body weight at 140 days, and subsequent eggs per hen housed. The groups were fed the same diet during rearing, but the feed was allocated differently each week to achieve the cumulative differences. There were apparently no great differences in female body weight, but when the birds were photostimulated at less than ~22,000 kcal cumulative ME and ~1200 g CP, there was a reduction in eggs per hen of ~15. This suggests that there was a minimum nutrient intake, irrespective of body weight, required to obtain acceptable levels of egg production.

A recent review of NCSU broiler breeder research flock data revealed that in 1988, females were grown to a 140-day body weight of ~2.0 kg with ~28,000 kcal cumulative ME. Comparative data from 1998 shows that this 2.0 kg body weight could be achieved with as little as 20,000 kcal cumulative ME. This difference is probably due to the remarkable genetic progress made in broiler feed conversion. This may explain why photostimulation has been required to be adjusted from 126 days in 1983 to 154 days or later today. With improved feed conversion, it may simply take longer to accumulate the necessary nutrition for a proper response to photostimulation.

Fertility In The Female
The fact that cumulative CP nutrition at photostimulation can have a significant effect on female fertility has been clearly defined (Walsh, 1996; Walsh and Brake, 1997, 1999). The female contributes to fertility through mating receptivity and spermatozoal storage in special sperm host glands in the oviduct. This was demonstrated by VanKrey and Siegel (1974) where broiler line genetic selection proceeded on nutrient-dense broiler diets while typical lower protein and energy rearing diets were used for parent stock. Evidently, inadequate CP (amino acid) nutrition prior to photostimulation, irrespective of female body weight, leads to poor persistency of fertility.

Data summarized in Figure 2 show cumulative fertility for several female experimental groups from 28 to 64 weeks of age along with the fertility for the last 8 weeks of production (57 to 64 weeks of age). The latter is a good indicator of persistency of female fertility as all males were managed in a similar manner across all experimental groups. It is also important to note that the effects of nutrition and management during rearing and the early breeding period are often seen only very late in the breeding period. From Figure 2, it is clear that there is a minimum cumulative CP intake of ~1200 grams CP or greater at photostimulation (141 days) for females, irrespective of body weight. This projected minimum assumed that the total lysine, on a corn-soy-based diet, was 5% of crude protein and methionine + cystine were 83% of lysine.

Feeding Programs For Yield-type Broiler Breeders
It has been noticed in the USA that females reared with males often produce more eggs than females reared sex-separate. In order to understand this observation, a study (Mixgrow) was conducted to determine the effect of mixing males with females at different ages. Yield males were fullfed on an 18% CP diet until mixed with females at two, four, six, or eight weeks of age. The yield females received an 18% CP diet for one week followed by a 15% CP diet to photostimulation. The feeding programs for the various male treatments are shown in Figure 3 along with the female feeding program. The female feeding program used was one that had been shown to be successful for the "standard" type of broiler breeder pullet. Female body weights were virtually identical across male treatments. The male body weights reflected a dose response to increased amounts of feed prior to mixing. Cumulative fertility is shown in Table 2.

These fertility numbers are lower than optimum because males and females were fed together after 21 weeks of age to exaggerate the effect of cumulative nutrition during rearing and to allow the males to be exposed to a decreasing feed allocation after 35 weeks of age. In spite of this, some of the pens with the eight-week mixed males exhibited fertility in excess of 90% at 64 weeks of age without any body weight control or separate feeding. The later mixing age males (six and eight weeks) were more resistant to the feed reduction after peak egg production because they reached sexual maturity with a greater nutrient reserve. A conservative estimate of cumulative nutrient consumption by the males to 21 weeks of age (photostimulation) based upon planned male and female intake is shown in Table 2. The actual feed intake of the males mixed with females at six weeks of age (as an example) and that of the females can be estimated from the body weights taken from all birds every two weeks using the formulas of Combs (1968). The results are projected in Figure 4.

The males consumed about 125% to 150% of the female feed intake depending upon age when mixed and body weight. This would give an actual cumulative ME intake of over 34,000 kcal and 1600 grams of CP for both the six week and eight week mixed males. This agrees with other data from our laboratory with separate-grown males. The data also show that the real pattern of female feed consumption (Figure 4) differed significantly from the programmed pattern, especially after 14 weeks of age. This must be extremely important as females that were grown sex-separate on the programmed female feed amounts laid ~35 fewer eggs per hen. These data (and field experience) suggest that larger feed increases late in rearing (in blackout where there is little reproductive development) for "yield-type" pullets results in excessive body weight and excessive "fleshing" (breast meat development). Much has been said about the need for good "fleshing" in "standard" strains of parent stock but the situation is much different for the "yield-type" pullet. Excess breast meat appears to reduce egg production.

We must be careful to not give too much feed too early (before onset of lay) as we may simply increase female body weight, primarily breast meat, and cause reproductive problems such as peritonitis. The excess breast meat probably increases maintenance and inhibits reproductive development. This may be why heavy breasts relative to fat pad develop when feed increases are too rapid in "yieldtype" females. These birds with excess breast meat relative to fat pad tend to exhibit a reduced appetite in hot weather (even in tunnel-ventilated and evaporatively cooled houses), increased susceptibility to heat stress, poor peak egg production and lay poorly thereafter. A conservative feeding approach both before and after photostimulation would be advisable with "yield" females until one becomes familiar with the particular strain of broiler breeder in the specific situation. It is better for the hens to be late coming into production than to exhibit high mortality and poor egg production. These problems are uncommon with a "standard" type broiler breeder hen.

In a manner similar to the need to modulate any large increases in feed intake, diets should be formulated to minimize abrupt changes in composition that will create situations that are similar to abrupt changes in the feeding rate. A single dietary ME for all diets is recommended to assist production managers maintain consistent feed increases. Similarly, modern broiler breeders may respond robustly to abrupt changes in protein with an unexpected increase in body weight. A smooth transition among starter-grower-breeder diets or starter-grower-prebreeder-breeder diets should be considered during feed formulation. It is suggested that total lysine levels be ~5% of crude protein and methionine + cystine be ~0.60-0.63% of the diet for most feeds. It is probable that "yield-type" females perform better with a slightly lower protein breeder feed than can be fed successfully to a "standard" female. A 16% CP diet with ~0.80-0.82% total lysine should be sufficient to support egg production without producing excessive amounts of breast meat.

Dietary Protein And Metabolizable Energy For Broiler Breeder Males
Few data exist that link intake of ME during rearing to breeding performance. However, the findings of Vaughters et al. (1987) indicated that a relationship between ME consumed during rearing and fertility may exist. Our data (Table 2 above) suggest a minimum cumulative ME intake of ~30,000 kcal prior to photostimulation. However, most data suggest that reproductive fecundity is directly related to daily ME intake during the breeding period and that daily ME intake should somehow be proportional to body weight and body weight gain. It should be stated that Parker and Arscott (1964) and Sexton et al., (1989b) observed that decreased fertility was preceded by decreased dietary ME intake during the breeding period. In cages, Attia et al. (1995) fed Ross males 300, 340, or 380 kcal ME per day. They found no fertility differences, but did note increasing testis weights with increasing ME intake. In floor pens from 26 to 60 weeks of age, Attia et al., (1993) found the 300 kcal ME males to weigh less and have lower fertility than the males consuming 340 and 380 kcal ME per day. These data clearly show a differential effect of ME intake in cages versus floor pens due to the difference in relative activity levels. All the birds in cages probably received enough ME to satisfy their reproduction requirements. However, in the floor pens, it appeared that the birds on the lowest ME intake did not receive enough nutrients for reproduction due to the increased maintenance requirement required for increased activity.

It is also very interesting that these authors found a dose-related decrease in 42-day broiler weights with decreasing ME allocation to the breeder males. Presumably, these data suggest that males that have the potential to produce the largest broilers require more ME to breed in natural mating conditions. These data also suggests that excessive efforts to control male body weight can reduce broiler performance.

Confusion about optimum diets for males began when Wilson et al. (1987a) fed 12%, 14%, 16%, and 18% CP diets to males from four to 53 weeks of age. The 10 males used per treatment were placed in cages at 14 weeks of age. There was no lighting program detailed in the manuscript and is presumed to be natural daylight during rearing with artificial supplementation at some unspecified point. Cumulative CP to 21 weeks was 1220 grams and 1385 grams, respectively for the 12% and 14% groups. This total increased to 1650 grams at 27 weeks of age for the 12% group, the time of the first artificial ejaculations in this particular study. By comparison, males in natural mating conditions need to mature by ~22 weeks of age for best results. No significant differences in semen volume, testis weights, and spermatozoal concentration among the diets were found, but significantly more males produced semen as a result of abdominal massage on the 12% and 14% CP diets. Although there were no significant differences in body weight among the treatments, the 12% and 14% males did exhibit a generally more consistent body weight gain throughout the breeding period. It is important to note that all the diets used in this and subsequent studies from this laboratory at Auburn University had total lysine as 5.1% to 5.3% of total CP and total methionine + cystine as 75% to 77% of lysine in corn-soy based diets. This was similar to the dietary approach used by our laboratory at North Carolina State University, but may differ somewhat from observed commercial practice where low protein male diets are often not properly balanced. We like to have lysine as 5% of CP and methionine + cystine in the range of 75% to 83% of lysine.

In a recent study from the same laboratory at Auburn University, Zhang et al. (1999) made a comparison of 12% and 16% CP diets from four to 52 weeks of age. As in previous reports, there was a higher percentage males producing semen as a result of artificial ejaculation, but there were again no differences in semen quality or quantity. Given that differences in semen quality or quantity are not usually found as a result of difference in CP intake, one has to question if the reported higher percentage males producing semen as a result of artificial ejaculation is simply an artifact of the semen collection process with birds that may vary in body conformation. This response (percentage males producing semen) seems to consistently take the form of a dose response while all other variables show no such dose response. In the experiment of Zhang et al. (1999), the daily ME allowance was 325 kcal during the breeding period. As shown later, this energy allocation is slightly low. A gradual decline in semen production with increasing age and body weight was observed, irrespective of CP level of the diet. The authors interpreted this to mean that continued body weight gain was necessary to maintain optimal male reproductive function. Continued body weight gain clearly would require appropriate increases in ME allowances as body weight increased.

The extensive French work, led by de Reviers (de Reviers, 1977; de Reviers, 1980; de Reviers and Williams, 1984; de Reviers and Seigneurin, 1990) showed that heavy weight line males exhibit greater problems with persistency of testes size and semen production when compared to medium weight male lines. Photostimulation of heavy weight line males typically result in a robust, but short, response in testicular weight and semen production while medium weight male lines exhibit better persistency of these traits. It is presumed, as no nutritional data were given in these reports, that both male lines were fed typical low-density diets. It is further presumed that these diets may have been marginal for the heavy line males, based upon calculations from North Carolina State University data, in a manner similar to that shown in Figure 1 above for quail (Lilburn et al., 1992). The problem of lack of persistency of semen production can be solved, if one is using artificial insemination, by simply not photostimulating the birds and allowing the males to reach sexual maturity at their own pace, presumably after consuming sufficient nutrients.

Therefore, if a bird were deficient in CP during the growing period the effects would be most noticeable around the onset of sexual maturity. Vaughters et al., (1987) fed diets containing 12%, 15%, or 18% from 24 to 27 weeks of age (early breeding period) and reported initial fertility to be highest for the 18% CP diet in natural mating conditions. This suggests a relationship between sexual development and the initiation of reproductive function. Turkey and broiler breeder hens are both known to exhibit an intense desire to mate prior to the onset of egg production. When turkey hens were inseminated during this period of prelay receptivity, there was a significant increase in life-of-flock fertility even in the presence of marginal spermatozoal numbers (McIntyre et al., 1982). This early mating presumably leads to enhanced spermatozoal storage. This may also be true for broiler breeders. It is clear that broiler breeders that exhibit low initial fertility under commercial natural mating conditions, where sexual maturity is needed at about 22 to 24 weeks of age, have difficulty achieving optimum fertility at later ages.

Although there appears to be an impact of CP during the growing period on fertility during the breeding period, dietary CP appears to have less impact during the breeding period. Diets from 5% to 16.9% CP have produced similar results in cages (Arscott and Parker, 1963; Buckner and Savage, 1986; Revington et al., 1991). The reason that these previous workers did not see more differences in fertility due to breeder dietary CP was probably due to the fact that their experiments were often initiated later in the breeder period (after 28 weeks of age). In these experiments, it appears that the birds were not marginal in CP before the experimental diets were applied, which made it difficult to detect fertility differences due to differences in breeder dietary CP. These data also suggest that low protein male feeds should not be used before sexual maturity is complete.

Data from our laboratory suggest the minimum cumulative CP intake required prior to photostimulation for broiler breeder males involved in natural mating to be on the order of 1600 grams, as compared to the 1200 grams required for female. We have found that it is possible to achieve this nutrient target with diets ranging from 12% CP to 17% CP. Moreover, our data, shown below, demonstrate the interaction of body weight and feeding program that influence male reproduction so profoundly. Figure 5 shows the feeding program for a research flock coded as BB-15. The broiler breeders were the Ross 308 package but the data are illustrative of our data with Cobb 500 and Arbor Acres Yield broiler breeder packages as well. All of these birds were reared separately from the females and fed sexseparate during the breeding period.

The combination of feeding program and diet produced an interesting effect on fertility as shown in Figure 6. The concave reared males experienced a decrease in body weight from 40 to 48 weeks of age and this is reflected in the transient decrease in fertility observed in Figure 6 for both the 12% and 17% CP reared males. The effect was more pronounced for the 17% CP males that were slightly larger and evidently less resistant to the imposed feeding deficiency. The problem was corrected by a five grams increase in daily feed allocation for the males. The cumulative intake of nutrients at 21 weeks of age were 1568 g CP and 36,593 kcal ME for the 12% males and 2123 g CP and 36,593 house was at 23 weeks of age. Again, the data suggest that if the minimum nutrition is adequate, it is not important what dietary protein level is used to achieve the goal. The males with the most consistent body weight gains produced the best fertility.

Body Weight In Broiler Breeder Males
It has long been clear that feed restriction to control body weight is both obligatory and beneficial in broiler breeders. However, excessive feed restriction of males during part or all of the growing period has been associated with decreased early fertility (Lilburn et al., 1990). Based upon the discussion above, it is thought that this effect is due to insufficient cumulative nutrition at photostimulation.

The major impetus for sex-separate feeding during the breeding period was the observation that poor fertility was associated with overweight males (McDaniel and Wilson, 1986; Duncan et al., 1990; Fontana et al., 1990; Mauldin, 1992) and separate feeding was believed to be necessary to control male body weight. However, caged males fed near ad libitum are known to exhibit excellent spermatozoal production (Parker and Arscott, 1964; Sexton et al., 1989a). This suggests that an appropriately controlled feed allocation rather than severe restriction is required. It is likely that overly severe feed restriction has actually caused fertility problems due to reduced mating activity as a result of caloric deficiencies. This may help explain the observations of Hocking (1990) who performed experiments with males in floor pens with natural mating during the breeding period. He found a curvilinear relationship between body weight and fertility. This implied that if body weight were too low or too high there would not be optimum fertility. He observed that underweight males were not physiologically sufficient while overweight males often were physically incapable of completing the mating process. He suggested an optimum body weight for optimum fertility that changed with age. He concluded that restricted control of body weight should allow an increase in body weight with age of the male.

We conducted a study to examine this inconsistency. We found that a decrease in fertility coincided with a decrease in female feed allocation and an increase in male body weight in situations where males were fed with females. In a similar manner, a decrease in male feed allocation in situations where males and females were fed separately caused a transient decrease followed by an increase in male body weight coincident with a decrease in fertility. Thereafter, fertility again increased when the feed allocation was increased in the separate-fed males. Male body weight was better controlled and fertility improved when the male feed allocation was increased slowly rather than decreased.

Another interesting study is summarized in Table 3 where groups of males in floor pens (without females) were fed various amounts of feed from 25 to 48 weeks of age. As shown in Table 3, the males that consumed the most feed had the lowest body weights. This is consistent with other data where increasing feed actually did a better job of controlling body weight than did decreasing feed.

What can be the explanation for the paradox shown above? As an example, a typical male at ~30 weeks of age will weigh ~4.00 kg (8.8 lbs.). The daily maintenance requirement at ~21°C (70°F) is ~306 kcal while that of a 4.45 kg (9.8 lbs.) male at ~45 weeks of age would be ~329 kcal. Unless there has been an increase in daily feed allocation proportionate with the body weight gain, the 4.45 kg male would have to exhibit negative growth (lose body weight) as the male mobilized body reserves to make up the energy deficiency. This would continue until the energy reserves of the larger male were exhausted. At this time, mating activity would decrease as testosterone levels decreased. The male would then gain body weight because of inactivity. This could lead one to conclude that males do not necessarily cease mating because they gain excessive body weight, but that males gain excessive body weight because they cease mating!

In the same way that our best egg production occurs when the females slowly gain body weight, our best fertility occurs when the males slowly gain body weight. As the male does not exhibit a decline in daily energy requirement as does the female (due to decreasing egg production) it is suggested that the daily feed allocation be increased at least one gram every three to four weeks during the breeding period such that the male body weight increases slowly but consistently and remains within limits established by practical experience and known to be associated with good fertility. Ken Krueger (1977) found that male turkey semen production could be maximized for the entire life cycle by maintaining the toms on a feeding regimen that supported a consistent weekly body weight gain. Any loss in body weight was associated with a decline in semen production.

Broiler Breeder Male Mortality

The mortality of "yield-type" broiler breeder males during the laying period has become a costly problem for the USA poultry industry. The average male mortality from 22 to 64 weeks during the years 1995 to 1999 was approximately 43% (AgriStats, Inc., 6510 Mutual Drive, Fort Wayne, IN 46825). The cause of the majority of this mortality is unknown. To test a theory about the cause of this high mortality, Ross 308 females and non-dubbed Ross males were raised sexseparate on either a "linear" or a "concave" feed allocation program. One group of males was reared with females on a "mixed" program. Birds were grown on a daily 8-hour light and 16 hour dark lighting program and both feed and water were controlled. At the end of 21 weeks, the birds were moved to a curtain-sided laying house and photostimulated. There were the three male treatments shown in Figure 7. "Linear" grown males received constant feed increases of 2.4 g per male/week from four to 28 weeks. After 28 weeks, males received a constant feed amount of 117 g (342 kcal ME) per bird (7 g more than used in Figure 5). All separate grown males received the same amount of cumulative feed through 21 weeks that resulted in a cumulative CP intake of 1600 g and a cumulative ME intake of 32,000 kcal per male at photostimulation at 21 weeks of age.

Table 4 displays the male body weights. Males grown intermingled (mixed) with females had significantly lower body weights at 12 and 16 weeks when compared to the separately grown males. Separately grown males on the "linear" program had significantly higher body weights than separately grown males on the "concave" program. However, there were no differences in body weight due to treatment after photostimulation (22 weeks). All males had similar body weights at 22, 26, 28, 40, and 52 weeks of age.

Table 5 displays the percentage male mortality. During the early breeder period (22-29 weeks), mortality in the two groups of separately grown males was similar. It appeared that the "mixed" grown males had less mortality during this period although these differences were not statistically significant. Males grown separately on the "linear" program or "mixed" with females had significantly higher mortality from 30 to 44 weeks when compared to males grown separately on the "concave" program. From 45 to 64 weeks, "linear" males numerically had the highest mortality with "mixed" and "concave" males having similar mortality. When mortality was compared from 30 to 64 weeks, "concave" males had significantly lower mortality when compared with the "linear" males. "Mixed" males were intermediate. This same trend was observed overall (22-64 weeks). All data indicated that males grown on a "linear" feed allocation program exhibited higher mortality than males grown on a "concave" feed allocation program. It appears that the majority of the mortality due to "linear" feeding can be expected to occur between 30 to 44 weeks of age.

It appeared that 117 g of feed (342 kcal ME) per male per day was adequate to keep males grown on a 17% CP diet slowly gaining weight from 28 to 60 weeks of age under our current research management that utilizes strict male and female exclusion grills. Fertility was excellent with these males. However, under commercial conditions, a gradual increase in male feed allocation would be advised. Therefore, it appears that the feed allocation program used during the growing period in association with the time of photostimulation can influence broiler breeder male mortality. It appears that this occurs irrespective of body weight. The various groups of males employed in these experiments exhibited average body weights that were not remarkably different. Thus, one can conclude that management of feeding programs should take limited precedence over body weight management.

Overview Of Separate Male Rearing

Males may successfully be reared separately from females throughout the growing period. Careful attention to the feeding program must be exercised as demonstrated by the field observations outlined below. There has been much discussion about optimum male BW at four and 20 weeks of age. Table 6 shows the relationship between BW and peak hatchability from a commercial company experiencing a fertility problem. Inspection of Table 6 shows little relationship between BW and hatchability, but a graphical summary of the various feeding programs, irrespective of BW, used to grow these males revealed a clear relationship between feeding program and peak hatchability (Figure 8). A thorough examination of all available data suggest a minimum required cumulative nutrient intake from day old to photostimulation of ~1600 g CP and ~32,000 kcal ME per male and a specific feeding program approach is required to minimize mortality and maximize fertility.

Conclusion
We can conclude that the amount of nutrients a bird has available throughout its life impacts fertility and egg production. Metabolizable energy (or feed allocation) available to the bird during the breeding period is directly correlated to fertility, egg production and body weight. Protein accumulated in the bird during rearing influences the age of sexual maturity and the level of initial fertility for both males and females. Dietary CP has the largest impact during the grower and prebreeder periods, as this is when most of the CP required for initial sexual development is accumulated. Body weight and house temperature need to be controlled within certain limits throughout the life of the flock, however temperature and body weight management is most critical late in the breeding period because body weight is greatest at this time. The data clearly show that no specific diet has more or less utility for a male broiler breeder. Diets ranging from 12% CP to 17% CP can be fed provided that the cumulative intake of CP to photostimulation is sufficient to support initial sexual development. However, it is clear from practical experience that changing from a moderate or high CP feed to a low CP feed prior to sexual maturity has adverse effects on broiler breeder fertility. It is most important to maintain consistent body weight gain throughout the life of the broiler breeder. Abrupt increases or decreases in body weight are clearly associated with changes in fertility and egg production. This infers a need to closely align ME intake to maintenance requirements that are driven by body weight and temperature. In summary, all the rules for the "standard" broiler breeder remain basically true, but more attention must be paid to these details. The most obvious exception to the basic rules is that excessive "fleshing" can be detrimental in the yield-type female because it can increase sensitivity to environmental temperature, reduce egg production and appetite, and increase mortality.

Special Notes And Acknowledgements
Some estimates of metabolic energy requirements in the text were based upon the formulas of G. F. Combs, 1968, page 86 in the Proceedings of the Maryland Nutrition Conference for Feed Manufacturers. These estimates have been found to be reasonably accurate, but may need to be adjusted slightly for strain and age effects and should be used with some caution. Portions of this manuscript were excerpted from the Proceedings of the Poultry Beyond 2005 Conference held in Rotorua, New Zealand in February 2001 and from the Proceedings of the Australian Poultry Science Symposium held in Sydney in February 2001.


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