aminoacizi ideali

The Ideal Amino Acid Requirements and Profile for Broilers, Layers,

and Broiler Breeders

Craig Coon Poultry Science Department

University of Arkansas

The Ideal Amino Acid Requirements and Profile for Broilers, Layers, and Broiler Breeders

The importance of utilizing the correct amount of balanced dietary protein and amino acids for poultry is a high priority issue for several reasons. First, the costs of protein and amino acids are some of the most expensive nutrients in feeds/per unit weight. Selecting the correct level of amino acids needed for your company becomes a critical economic decision. Second, the environmental concerns about nitrogen losses in animal waste are similar to the on-going problems and litigation associated with phosphorus losses. Nitrogen has also been shown to have a negative affect on our fresh water supply and integrators will need to closely monitor and manage the nitrogen levels in their poultry waste. Third, nutrients that can cause the largest problems in heat stress conditions for animals are poor quality dietary proteins and amino acids. The reason dietary protein and amino acids cause such a high heat increment from metabolism is the inefficient process of incorporating feed protein and amino acids into body or egg proteins. The formation of new body or egg proteins from both endogenous and dietary amino acids can be inefficient with regard to using available metabolic energy. A large amount of metabolic energy is utilized causing additional body heat production in poultry during the process of eliminating excess nitrogen. The nitrogen not used in body gains or egg production must be converted into a non- toxic metabolite called uric acid and eliminated from the body. The production of the nitrogen waste product, uric acid, requires a significant amount of metabolic energy that takes away from the energy needed for growth and egg production. The impact of increasing additional heat production during protein and amino acid metabolism for poultry housed in hot climates will be a significant reduction in feed consumption and reduction in poultry performance. In most cases, the first limiting nutrient in heat stress conditions is not protein and amino acids but an overall reduction in energy intake. Nutritionist working for companies with poultry housed in hot climates and trying to save money using poor quality protein sources that are lower in amino acid digestibility will costs the company more money because of less meat gain or egg output. The concept of formulating broiler, layer, and broiler breeder feed on an ideal protein basis decreases the main problems associated with protein and amino acid formulations. An ideal protein and amino acid profile in a feed means that the essential and non-essential amino acid levels exactly provide the requirements leaving no extra amino acid nitrogen for elimination. In reality, a practical feed formulation based on an ideal protein and amino acid level set at exact requirements is not possible. At the present time, the best ideal protein and amino acid formulation would consists of selecting highly digestible protein sources that complement each other, formulate on a digestible amino acid basis, and utilize commercially available

free amino acids to help supply requirements for methionine, methionine plus cystine, lysine, and threonine. The amount of protein that will be selected by a computer feed formulation program will be the protein needed to provide the next limiting digestible amino acid that is not controlled by adding commercial amino acid sources. The reason it is important to formulate on a digestible amino acid basis is the ability to formulate for optimum levels of protein and amino acids without using such large margins of safety for poor digestible protein sources. This allows nutritionist to utilize lower levels of crude protein in formulations and research has showed that for each 1% reduction in dietary crude protein through improved amino acid formulations, there is a 10% reduction in nitrogen losses in poultry waste. The metabolic systems of the birds fed ideal protein and amino acid diets are not working as hard to eliminate the excess nitrogen which keeps them cooler providing more useable energy for productive purposes. In the future, additional commercial amino acids may become available through GMO technology making it easier to establish an ideal protein and amino acid diet for which all amino acids are balanced. The concentration of protein and amino acids in broiler diets will have a large impact on breast meat yield, feed/gain ratio, and number of days required to produce the appropriate body weight for each type of market. Depending upon genetic strain and the market objectives for each broiler complex, a broiler integrator will probably utilize several different protein and amino acid dietary programs. Higher levels of dietary protein and amino acids can be easier to justify if the marketable products that are being produced have higher value. The importance of dietary protein and amino acids for commercial layers is similar to the importance of these nutrients for meat birds. Commercial layers need both dietary energy and amino acids for egg numbers but the key nutrient for regulating egg size is primarily protein and amino acids. This becomes very important when trying to produce and maintain the optimum economical egg size from a flock. Primary breeders for commercial layers have genetically selected birds that can be light stimulated and brought into egg production much earlier than in the past. The early egg production has steadily increased the number of eggs per hen but has also increased the demands on dietary protein and amino acids to support larger egg size in these early eggs. There are many commercial layers fed with feed formulation programs associated with economic models that indicate when it is economically feasible to increase or decrease the concentration of dietary protein and amino acids in order to move up or stay at the present egg size. Another factor that will have a major impact on levels of dietary protein and amino acids that are needed for layers will be environmental conditions. Since dietary nutrient requirements for layers are based on daily intake, environmental factors such as temperature, humidity, air quality, ventilation rate, stocking density, and feeder space have a large impact on feed consumption and needed adjustments in feed formulation. Egg producers must utilize the most cost effective housing and environmental conditions available to minimize excess feed consumption and feed costs. A related factor that will change environmental conditions and feed consumption per hen for egg producers will be the

continuing outside pressure to provide environmental conditions requested by Animal Well Being groups. The greatest pressure at the present time to provide more cage space per layer is for egg processors that produce a liquid egg product and sell to large food chains. Layers provided more cage and feeder space have been shown to increase their daily feed intake which greatly affects the daily protein and amino acid intake. Current broiler breeders are fed between 24-26g of dietary protein and amino acids/breeder/day. Research has shown that this much protein and amino acids are not necessary and high protein breeder diets may negatively affect fertility and hatchability. Past Research has shown breeders fed 10% protein diets with adequate methionine and lysine can perform equal to breeders fed 16% breeder diets. The researcher also showed the breeders eliminated less nitrogen and also had higher fertility. The only difference was breeders fed the 10% protein diet produced smaller hatching eggs. Although the investigator did not observe a significant weight gain difference in performance studies between chicks hatched from the smaller eggs compared to chicks from breeders fed standard protein breeder diets, chick size is a key concern regarding broiler integrators selecting optimum breeder protein diets. Although, feed costs per hatched chick is a critical factor for an integrator, most companies will not take a chance on reducing dietary protein and amino acids because of the extreme value of quality hatching eggs and chicks. Obtaining equal performance and hatching egg production with modern ultra-high yield breeder type hens compared to standard breeders or other high yield breeders has been difficult. The modern breeder pullets and hens have the capacity to gain protein mass (fleshing) and weight quickly during the rearing period and also during the early stages of egg production. Breeder pullets are control fed from 10 days of age until completing the production period because of the their propensity to gain weight. Commercial primary breeders believe the modern ultra-high yield type pullet is extremely efficient in using dietary energy compared to their past counterpart and the pullets first priority may be in producing a quantitative amount of body protein mass (fleshing) with the second priority being the amount of body fat. Sexual maturity of these pullets shows a more consistent amount of body protein with variable fat levels. Many questions need answered about optimum feeding systems for the ultra-high yield type breeder with regard to protein and amino acid needs during both the rearing and production periods. Broilers

Factorial requirements for amino acids for both maintenance and growth are needed for broilers. Dramatic genetic changes have occurred in many commercial broiler lines during the past decade with regard to growth curves and breast meat yield because of the need for producing broilers suitable for different markets. Broiler breeder strains have been genetically selected for producing progeny that will gain weight quickly for the whole bird and cut-up markets or progeny being produced for further processing that ideally gain weight slower in the starter period and then rapidly gain protein

and breast weight later during the growing and finishing period. Broilers being produced for deboning need more time in the beginning to develop a strong skeletal system for supporting heavier weights. The amino acid profile needed for maintenance has been shown to be different than the profile needed to produce optimum weight gains (Baker et al, 1996; Coon et al, 1998). The percentage of the daily total requirement for amino acids that is needed for maintenance is minimal during the starter period but then increases as the broiler becomes larger. Factorial requirements for amino acids for both maintenance and growth would allow nutritionist to develop different amino acid requirements for different genetic lines of broilers and marketing situations depending upon the age, genetic growth rate, carcass composition, and overall body weight. Researchers have developed factorial amino acid requirements for both maintenance and weight gain for swine and the values are being successfully used in several commercial models utilized for determining nutrient requirements (Fuller et al, 1989). The improvement in N accretion efficiency and N excretion reduction can be obtained by matching more closely the amino acid composition of the diet with the amino acid maintenance and production requirement of broilers. Baker and Han (1994) reported that the amino acid requirements couldn’t apply to all birds under all dietary, sex, and body compositional circumstances. The researchers supported an idea of expressing the amino acid requirements as ideal ratios to lysine. The presence of multiple dietary, environmental and genetic factors could affect the amino acid requirements of broilers, however, the ideal ratio of indispensable amino acids to lysine should remain largely unaffected by these variables. Digestible Amino Acid Requirements for Maintenance and Growth The digestible amino acid requirements for maintenance of 10 to 21 and 32 to 43-day old broilers were evaluated in several individual broiler feeding studies. Five individually caged broilers were each fed one of four test levels of each test amino acid for the maintenance experiments.

The amino acid requirements for protein accretion or growth were determined by difference between the requirement for optimum protein retention determined in the previous section and the maintenance requirement. The digestible-amino acid levels in experimental maintenance diets were at 0, 5, 10, 15% and 0, 10, 15, 30% of NRC (1994) recommendations (using .89 digestion coefficient) for 10-21 and 32-43 day-old broilers, respectively (Table 4).

The total daily digestible-amino acid requirements were expressed as mg amino acid/day/kg BW0.75 to partition the total requirement into growth and maintenance. The amino acid requirements as mg amino acid /day/kg BW 0.75 were higher for 10 to 21-day old broilers (Table 5) compared to 32 to 43-day old broilers (Table 6).

In contrast, the percentage of digestible-amino acids needed for maintenance compared to the total digestible amino acid requirement increased with age. The average digestible amino acid requirements for maintenance was 6% of total daily digestible amino acid requirements for 10-21 day-old broilers (ranged from 1.4% for histidine to 11% for arginine). The average digestible amino acid requirement for maintenance was 22 % of total daily amino acid requirements for 32-43 day-old broilers (ranged from 17% for methionine and arginine to 29% for cystine).

Dietary digestible lysine needed for maintenance for both age groups was determined to be zero. The authors believe the metabolic turnover of lysine may have provided a positive nitrogen accretion for the experimental broilers even when the broilers were fed no dietary lysine. The ratio of amino acids to lysine required for growth (total daily requirements minus maintenance) for both the 10-21 and 32-43 day old broiler was found to be strikingly similar to the ratio of amino acids to lysine determined for the body composition of the broilers.

The research indicates that probably the best way to express daily maintenance requirements for different sizes of broilers would be to use mg amino acid/kg carcass protein instead of using the traditional mg/day/kg BW0.75. The 32-43 day old broilers had a daily maintenance requirement (mg/day) of amino acids that were 15.38 times greater than 10-21 day old broilers, 3.29 times higher based on mg amino acid/day/kg BW0.75, and only 1.66 times greater expressed as mg amino acid/day/kg carcass protein (Table 7).

Emmert and Baker (1997) and Baker et al. (1996) have reported the threonine, valine, and lysine maintenance requirements for young broilers. The amino acid values reported by the Illinois researchers are very similar to research reported by Hrubý et al.(22)(Table 8). Hrubý et al. (1998) could not detect a lysine response for either the 10-21 or 32-43 day old broiler whereas the Illinois group showed a very small requirement compared to the other amino acids. Leveille et al. (1960) also reported no measurable lysine requirement for leghorn roosters (Table 8) but found almost all other daily amino acid requirements were greater than found for the broiler with the exception of phenylalanine, histidine, and arginine.

The partitioning of the digestible amino acids into maintenance and growth allows for an estimate of amino acid utilization for amino acids above maintenance. The amino acid content of the fat-free carcass and feathers along with the protein gain of those components provides an amino acid accretion value. The determined amino acid requirement for growth (total digestible requirement-maintenance) can be divided into the amino acid accretion value (carcass amino acid analysis x protein gain) and a utilization value can be obtained. The utilization of amino acids for production and maintenance are shown in Table 9 for 10-21 day old broilers (ave.= 71.16 %) and in Table 10 for 32-43 day old broilers (ave.= 61.70). The utilization efficiency of amino acids are about 10 percentage points higher in the younger broiler. The larger gain in feather weight during the 10-21 day old broiler may have contributed to the high 93.5 % cystine utilization compared to 64.9 % for older broilers. The above 100 % utilization of glycine and serine is probably caused by the ability of the bird to synthesize these semi-essential amino acids.

Figure 4 shows the importance of developing different maintenance and growth requirements for each of the amino acids. The carcass percentage of both lysine and methionine greatly increases in the 42 day broiler compared to the 21 day broiler because the breast becomes a

predominant portion of the total carcass. The breast contains a higher percentage of lysine and methionine than in other body components (Table 11). The overall increase in carcass lysine and methionine in amino acid composition in older broilers because of the increase in breast meat percentage in older broilers is probably the reason that these amino acids have been shown to increase breast meat yield (Table 12). The amino acid requirements for different genetic broiler lines will be partially dependent upon the amino acid content of each body component (i.e. breast, thigh, drum) and the extent to which the carcass components change as a percentage of the whole bird. Arkansas Broiler Research The objective of the Arkansas broiler study was to establish the ideal digestible AA profile relative to digestible lysine for broiler wt gain, feed/gain ratio, uric acid excretion, and nitrogen /amino acid accretion using broken line, polynomial, and exponential regression models. Seven dose-response experiments were conducted with each experiment determining two AA requirements.

Cobb 500 male broiler chicks were fed a corn-soy basal diet (3160 kcal ME, 19 % CP equivalents) with AA mixture fortified with all essential AA except the test amino acid. The broiler chicks were fed 8 levels of test AA ranging from 60 to 130% of AA standard (NRC profile, 1994) relative to 1.2% digestible lysine.

The ideal digestible AA profile relative to digestible lysine from broken line analysis for wt gain was calculated to be 99% Arg (105% if set Lys 0.1% higher), 135% Gly+Ser, 34% His, 77% Ile, 124% Leu, 35% Met, 32% Cys, 67% Met+Cys, 63% Phe, 62% Tyr, 125% Phe+Tyr, 75% Thr, 19% Trp, and 94% Val (Table 13 ). The profile from broken line analysis for feed/gain ratio was calculated to be 105% Arg (117% if set Lys 0.1% higher), 125% Gly+Ser, 37% His, 76% Ile, 127% Leu, 36% Met, 34% Cys, 70% Met+Cys, 65% Phe, 60% Tyr, 125% Phe+Tyr, 70% Thr, 19% Trp, and 84% Val (Table 13 ). The ideal digestible AA ratio relative to digestible lysine from broken line analysis for uric acid excretion was calculated to be 103% Arg (114% Arg, Lys 0.1% higher), 117% Gly+Ser, 32% His, 78% Ile, 132% Leu, 32% Met, 28% Cys, 60% Met+Cys, 65% Phe, 64% Tyr, 129% Phe+Tyr, 65% Thr, 19% Trp, 84% Val (Table 13).

The amino acid profile from broken line analysis for AA accretion and nitrogen accretion were similar and were calculated to be 98% Arg (104% Arg, Lys 0.1% higher), 142% Gly+Ser, 37% His, 81% Ile, 139 % Leu, 38% Met, 35%Cys, 73% Met+Cys, 67% Phe, 59% Tyr, 126% Phe+Tyr, 74% Thr, 20% Trp, 81% Val (Table 13 ).

The profile for amino acid requirements are also listed for exponential (Table 14) and polynomial regressions (Table 15). The requirement for digestible Lys based on polynomial analysis was 1.174% for wt gain, 1.178 % for feed/gain ratio, 1.182 % for nitrogen accretion, 1.169 % for lysine accretion, and 1.207 % or uric acid excretion. The CP requirement based on polynomial analysis was 19.32% for wt gain and 21 % for feed/gain ratio.

The performance of chicks fed experimental diets to compare the different amino acid profiles in a 10 day feeding study indicated that the profile determined with polynomial regression for feed/gain ratio produced the best performance for weight gain, FCR, nitrogen accretion and lowest uric acid excretion (Table 16). The rationale for the best chick performance for chicks fed the diets with the profile based on polynomial regression is because the first limiting amino acid, methionine, was the highest which then provided the best performance.

All chicks were fed the lysine requirements based on feed/gain ratio determined with polynomial regression to equalize the dietary amino acids and compare the profile determined with each parameter. The broken line regression produces amino acid requirements that are significantly lower than determined with either exponential or polynomial regression but is considered the optimum system to truly determine amino acid profiles related to lysine. All amino acids requirements determined with the broken line regression are limiting for optimum performance and the ability to compare other amino acids to lysine is more realistic than when the requirements and profiles for exponential and polynomial regressions are utilized.

Broiler References Austic, R. E., 1994. Proc. Maryland Nutr. Conf. 114-130. Baker, D.H., C. M. Parsons, C. M. Fernandez, S. Aoyagi and Y. Han. 1993. Proc. Arkansas Nutr. Conf. 22-32. Baker, D. H. and Y. Han, 1994. Poultry Sci. 73:1441-1447. Baker, D. H., 1996. Nutrient Management of Food Animals to Enhance and Protect the Environment. Kornegay, E. T. (ed.), Lewis Publishers, New York, p41-53. Baker, D. H., S. R. Fernandez, C. M. Parsons, H. M. Edwards III, J. L. Emmert, and D.M. Webel, 1996. J. Nutr. 126:1844-1851. Baker, D. H. 1997. Ideal amino acid profile for swine and poultry and their applications in feed formulation. Kyowa Hakko Technical Review-9. Coon, C., M. Hruby, and K. Leske, 1999. Proc. Maryland Nutr. Conf. 26-42. Dutch Bureau of Livestock Feeding, 1996. Schutte, J. B. (ed.), CVB report No. 18. Emmert, J. and D. H. Baker, 1997. J. Applied Poultry Res. 6:462-470. Fuller, M.F., R. McWilliams, T.C. Wang, and L.R. Giles, 1989. Brit. J. Nutr. 62:255-267. Hrubý, M., K. Leske, and C. Coon, 1998. Poultry Sci. 77: Supp. 1, p56. Hrubý, M., K. Leske, and C. Coon, 1998. Poultry Sci. 77: Supp. 1, p56. Leveille, G. A., R. Shapiro and H. Fisher, 1960. J. Nutr. 72:8-15. Mack, S., D. Bercovici, G. De Grootte, B. Leclercq, M. Pack, J. B. Schutte, and S. Van Cauwenberghe, 1999. Brit. J. Poultry Sci. 40:257-265. National Research Council, 1994. 9th ed., National Acad. Press, Washington, DC. Stilborn, H. L., E. T. Moran, Jr., R. M. Gous, and M. D. Harrison, 1997. J. Applied Poultry Res. 6: 205-209.

Commercial Layers

The main objective of the layer amino acid feeding trials was to determine if the performance of layers fed low protein diets supplemented with essential or non-essential amino acids could be equal to layers fed 18% CP diets supplemented with methionine. Five thousand eight hundred and sixty six layers consisting of four different strains were fed experimental diets from eight to sixteen weeks in seven different experiments. The experimental diets were isocaloric containing 2900 kcal ME/kg and digestible amino acids were determined for the test diets. The response of each test amino acid was evaluated separately in two of the seven experiments by adding four supplemental levels to 14% protein diets. The 14% CP diets, except for the test amino acid, were supplemented with all essential amino acids providing amino acid levels contained in 18% CP control diets. The requirements for each of the essential amino acids are expressed as mg digestible amino acid/hen/day for hens producing approximately 50 g egg mass per day and also mg digestible amino acid/g egg mass to provide flexibility for producers utilizing strains that are producing more than 50 g egg mass per day (Table 17). Isoleucine and valine added to 14% CP diets significantly increased body weight gain and also had a larger effect on percent albumen and yolk than other amino acids. The addition of tryptophan to the low protein corn-soy-meat diets had no effect on layer performance. Some scientists have suggested tryptophan to be the third limiting amino acid for layers fed corn-soy diets, however, the Minnesota layer data does not support that. Non-essential amino acids added to the 14% CP diet did not improve performance and actually tended to increase feed consumption and decrease feed efficiency. The egg composition and performance of layers fed corn-soy-meat 14% CP diets with added methionine, lysine, isoleucine, and valine was equal to layers fed 18% CP control diets. The research showed that four different commercial layer strains fed 14% protein diets with added synthetic amino acids to provide an ideal protein performed equal to layers fed higher protein diets (Table 18). Nitrogen loss in excreta was 15 percent less for layers fed 14% protein diets supplemented with amino acids compared to layers fed 18% protein diets (Table 19). The ideal amino acid profile determined from the research at the University of Minnesota is shown in Table 20. The amino acid profile is related to lysine requirements for both the NRC (1994) suggested requirements and the average values obtained from the MN series of layer amino acid experiments. The MN layer arginine, threonine, valine, and methionine ratios to lysine are slightly higher whereas the TSAA, isoleucine, and tryptophan are slightly lower than the NRC ratios. Overall, the Minnesota suggested daily requirements of digestible amino acids are higher than the NRC (1994) suggested daily requirements of amino acids. The amino acid requirements of a modern white egg layer should be higher because of a sustained increased daily egg mass production compared to genetic lines of layers from the past. The order of limiting amino acids in a 14% CP corn-soy-meat and bone diet is methionine, TSAA, isoleucine, valine, lysine, arginine, threonine, and tryptophan. It takes approximately a 16%CP diet consisting of corn-soy-meat and bone meal to provide the correct levels of

digestible isoleucine and valine for a hen consuming 100 grams of feed daily. Presently, it is not economical to add synthetic isoleucine or valine to poultry diets.

Layer References Cao, Z., H. Cai, and C. Coon, 1995. Proc. MN Nutr. Conf., p257-289, Bloomington,

Minnesota.

National Research Council, 1994. 9th ed., National Acad. Press, Washington, DC.

W. Zollitsch, Z. Cao, A. Peguri, B. Zhang, T. Cheng, and C. Coon, 1996. Int’l Symposium on Nutritional Requirements of Poultry and Swine, p109-159, Department de Zootecnia, Universidade Federal de Viçosa, Viçosa-MG-Brazil.

Schutte, J.B., 1998. Proc. AR Nutr. Conf., p33-39, Fayetteville, Arkansas.

Broiler Breeders

Leeson (1999) recently reported as much as 10-15% differences in broiler breeder protein and amino acid requirements suggested by different breeding companies (Table 21). Leeson suggested that the differences could possibly be true breed differences but believes it is hard to rationalize considering our knowledge of breed-nutrition interactions. There are a limited number of papers describing the factorial requirement of amino acids for broiler breeders. Past research reports have either evaluated dietary protein levels or have discussed amino acid needs from empirical data without separating the requirements into maintenance, body weight gain, and egg production. Amino acid requirements for breeders need to be expressed on a factorial basis so that data can be extrapolated for differences in strains, ages, body weight, mature protein weight, body composition, egg size, egg composition, and egg numbers. Broiler breeders potentially may have more profound changes in body weight, egg weight, and egg mass than for a shell egg-laying hen, which enhances the need for developing a factorial model. The amino acid requirements suggested by some researchers in past research may reflect egg production that would be less than optimum with the present breeder hen. This review will emphasize a comparison of suggested amino acid requirements that are predicted based on using factorial models with requirements determined with the most current empirical experiments with applicable production levels. Harms (1992) and Lopez and Leeson (1994) have reported that many of the broiler breeder amino acid feeding studies are confounded by differences in dietary protein intake. The amino acid nutrition of broiler breeder males will not be discussed in this review. Methionine and Sulfur Amino Acids The problem of reviewing the requirements for methionine and TSAA for breeders is a lack of consistency by investigators in the amount of dietary cystine that was used in experimental diets. The actual methionine requirement needs to be determined with adequate dietary cystine being available to the breeder. A TSAA requirement should be the amount of dietary cystine that can be used by breeders along with the true need for methionine. If dietary methionine has to be used to provide cystine for breeders, the TSAA requirement will be different than a TSAA requirement when cystine is adequate. The conversion of methionine to cystine is equal on an equimolar basis or is approximately 80% on a weight basis (methionine molecular weight -149.2;cysteine molecular weight-121.2) for both broilers and laying hens (Cao et al., 1995). Some investigators include both a methionine requirement and a TSAA requirement. The methionine requirement of breeders reported by Bowmaker and Gous (1991) can be predicted with response coefficients for the Reading Model of 7.03 E (g egg mass/day) and 1.52 W (kg body weight). Although the researchers did not evaluate the carcass composition of breeders before and after feeding the experimental diets, they believe the body weight gain for breeders is primarily fat gain and not protein deposition. The simulated requirement for methionine using the response coefficients of Bowmaker and Gous (1991) for a 2.5 kg breeder producing 50 g egg mass per day is 355 mg/day.

Leeson and Lopez (1994) suggested breeder requirements at peak production could be simulated by using breeders weighing approximately 2.5 kg, gaining 100 g/7 days, and producing 50 g egg mass/day. The researchers also suggested the 40 week older breeder with decreasing egg production could be simulated with a body weight of 3.5 kg, gaining 30 g/7 days, and producing 40 g egg mass. The methionine requirement of the simulated older breeder using response coefficients of Gous and Bowmaker (1991) would only be 287 mg day. The response coefficients for the Reading Model are for the average breeder in the flock but the requirements would not be adequate for the high-producing breeders. The Reading Model provides the opportunity to compensate for the high producing breeder by using the flock Coefficients of Variation (CV) for body weights, rate of lay, and egg weight along with various ratios of amino acid cost compared to egg value. The requirements are not based on digestible methionine requirements but on total dietary methionine. The researchers suggested the efficiency of utilization of dietary methionine for egg output is approximately 65% when the breeders are laying at a minimum rate of 50%. The researchers did not calculate the TSAA or cystine requirement, however they used a summit diet that contained exactly 3.5 g/kg of methionine and 7,0 g/kg of TSAA. The researchers did not add additional methionine to the basal diet but utilized different amounts of a dilution diet to provide the test levels of methionine intake. The amount of cystine used in the summit diet by the researchers would minimize the conversion of methionine to cystine based on the assumption that approximately 1/2 of the TSAA requirement can be cystine. If an assumption is made that 1/2 of the TSAA requirement can be cystine, the TSAA of the average breeder weighing 2.5 kg and producing 50 g egg mass may be assumed to be 710 mg /day. The TSAA predicted requirement for the older breeder weighing 3.5 kg and producing 40 g egg mass would only be 574 mg/day with this data. A similar requirement of 750 mg of TSAA for 45 to 60 week old breeders producing an average of 43.6 g egg mass/day, weighing 3.0 kg at 45 weeks, and gaining 17g/7 day period has been reported by Kuana et al. (1988). Wilson and Harms (1984) suggested the methionine and TSAA requirement for breeders was 400 mg and 750 mg day, respectively, compared to previous recommendations of methionine intake between 400 - 478 mg/day and TSAA intake between 722-839 mg/day (1980). Wilson and Harms (1984) suggested breeders only needed 20.6 g protein/day instead of 23.4 g in the earlier recommendations. Cave et al. (1990) reported that breeders between the age of 33-44 weeks of age consuming 24.8 g of dietary protein per day that weighed 3.5 kg and were producing a maximum egg mass of 50.3 g/day needed 528 mg dietary methionine and 960 mg TSAA per day. The researchers reported that hens consuming 21.6 g protein/day, weighing approximately 3.5 kg, and producing maximum egg mass of 48 g/day needed 480 mg methionine and 912 mg TSAA/day. The average methionine and cystine requirement of breeders from 25 weeks to 65 weeks consuming 21.6 g protein and producing a maximum average egg mass of 40.6 g/day was also 480 mg methionine and 912 mg TSAA/day. The average methionine and cystine requirement for breeders consuming the 15.5 % protein diet (average intake of 24.8 g/day) from 25 weeks to 65 weeks of age, producing a maximum average egg mass of 40.7 g/day was only 384 mg methionine and 816 mg TSAA. The breeders consuming the higher intake

of protein produced an average of one-gram larger egg weights for the 33-44 week period as well as the entire 25-65 week period. The additional egg mass output of breeders fed the high protein diets for the entire 40-week period actually required less methionine and cystine per unit egg mass than the birds fed the low protein diets. Cave et al. (1990) suggested the high methionine and TSAA requirements determined from their research is justified because the egg mass output is 6 to 8 percent above previous reported methionine and TSAA studies. In a parallel study, Cave et al. (1990) reported the maintenance requirement of breeders for TSAA was 103.3-mg/kg body weight per day. The maintenance requirement for TSAA was 3 times greater than reported by Leveille et al. (1960) for White Leghorns on a per kg body weight basis. The researchers also suggested the response coefficients from the models of Bornstein et al. (1979) and Smith (1978) used for predicting amino acid requirements for laying hen egg mass output may not be accurate for broiler breeder hens. Cave et al. (1990) utilized the TSAA maintenance requirements of 103.3 mg/kg BW and response coefficients of Model B - Equation 2 of Smith (1978) for weight gain and egg output to predict the TSAA requirements from their production data to compare to determined empirical requirements. The researchers reported a 3.3 kg breeder gaining 2.5 g/day and producing 48.2 g of daily egg mass would have a predicted TSAA requirement of 798 compared to 912 from empirical data. The researchers reported the egg mass coefficients from the laying hen Model B - Equation 2 were lower than coefficients needed to make the model accurately predict the breeder requirement for amino acids. The researchers suggested broiler breeders would have a lower efficiency of utilization for amino acids needed for egg production because of a high incidence of internal laying (Hocking and Gilbert, 1986) and because of variable amino acid supply with restriction feeding programs for breeders. The NRC (1994) recommendations for methionine and TSAA for broiler breeders are 450 mg and 700 mg/day, respectively. Lysine Bowmaker and Gous (1991) utilized the Reading Model to determine broiler breeder coefficients of response for lysine for egg mass and maintenance. The researchers suggested 16.88 E and 11.2 W represented the lysine response coefficients for the average breeding hen. Bowmaker and Gous (1991) reported the coefficients of response for maintenance and egg output were significantly different than reported Reading Model coefficients for amino acid requirements for laying hens (McDonald and Morris, 1985). The coefficients of response per kg BW for breeder maintenance amino acid requirements are lower and the coefficients for egg output are higher than needed for laying hens. Bowmaker and Gous (1991) suggested the lipid reserve making up a large portion of breeder body weight may cause the lower coefficients for maintenance. The researchers also noted a large number of breeders had open laying cycles (less than 1 egg every two days or less than 50 % production) which created different response curves compared to amino acid response curves obtained with laying hens. The researchers suggested the efficiency of utilization for lysine used for egg production was 47 %. The researchers noted the lysine utilization for egg output was 57 % if breeders laying at a rate above 50% production were utilized.

McDonald and Morris (1985) and Emmans and Fisher (1986) have suggested the efficiency of utilization of amino acids for egg output for laying hens is between 75 to 85 %. The predicted lysine requirements for an average breeding hen using suggested body weights and egg output (Leeson and Lopez, 1994) that represent a typical peaking (2.5 kg BW and 50 g egg mass) and older breeder (3.5 kg BW and 40 g egg mass) are 872 mg/day and 714 mg/day, respectively. Soares et al. (1988) reported 45 to 60 week old broiler breeders required 915 mg lysine/day when consuming 18.5 g protein/day, producing an average 48 g egg mass/day, with a body weight of 3.5 kg at 60 weeks. Harms and Ivey (1992) reported the requirement of breeders for dietary lysine as determined from empirical data ranges from 823.6 mg for egg production, 806.1 mg for egg weight, and 818.7 mg/day for egg mass when the daily protein intake was at least 18.6 g. The researchers determined the requirement of lysine while feeding 167.8 g feed/day with diets kept isocaloric (3115 kcal/kg) containing protein levels ranging from 9.6-12.18 %. The researchers reported the amount of protein and lysine consumption was the controlling factor for body weight gain instead of dietary energy. The researchers observed the hens consuming the largest amount of protein and lysine gained the most weight and also produced the largest eggs. The possibility exist that the extra dietary fat in the breeder diets used in the higher protein diets may have had an effect on body weight gain because of the "extra caloric effect". Harms and Ivey (1992) believed the additional egg mass produced by breeders fed higher levels of protein and lysine would require extra dietary energy which would offset the "extra caloric effect" of the dietary fat. The separation of amino acid requirements for egg production, egg weight, and egg mass as reported by Harms and Ivey (1992) may be a difficult approach because Morris and Gous (1988) showed that laying hens partition amino acids for egg production and egg weight depending upon the severity of the deficiency. The researchers show that both egg weight and rate of lay are decreased proportionately with small deficiencies however with severe deficiencies in protein and amino acids the egg number is primarily affected. Harms and Russell (1995) re-evaluated the requirement of lysine in order to separate the affects of lysine and protein intake on egg output of 32-week-old breeders. The researchers fed 80 groups of hens a daily allowance to supply 165 g/day with six basal isocaloric diets. The six basal diets contained a range of protein from 8.9-11.46 % with corresponding lysine levels from .38-.545 %. The addition of lysine and methionine to the 8.9% diet did not improve the egg production and the researchers suggested another amino acid was limiting. The researchers determined that 845 mg lysine /day was required for maximum egg production, egg mass, and egg content. The 10.95 % protein diet containing .515 % lysine provided adequate lysine, however the 9.41% and 9.92% protein diet with supplemental lysine produced the same egg mass output. The scientists suggested the NRC (1994) recommended requirements of 765 mg/day for lysine were low. The equal egg mass output of breeders fed lower protein corn-soybean meal diets supplemented with methionine and lysine indicated the recommended protein requirement of 19.5 g may be higher than needed. The researchers indicated an intake of 15.53 g and 16.37 g protein with the low protein diets supplemented with methionine and lysine were equal to breeders consuming 18.07 g protein with only supplemental methionine.

Tryptophan Harms (1992) reported that tryptophan is the third limiting amino acid in corn-soybean meal diets with methionine being first and lysine second limiting. The researcher reported that only lysine and tryptophan added to low protein corn-soybean meal diets significantly increased egg production. The research should not be used to determine the tryptophan requirement for breeders because the egg content output with only methionine, lysine, and tryptophan supplementation was 5 g/day less than breeders fed a control 13.08% protein diet. The breeders were consuming 200 mg tryptophan per day. Previous research by Harms and Ivey (1992) evaluating the lysine requirement for breeders determined that a tryptophan intake of 170 mg day with 16.72 g in a corn-soybean protein diet was satisfactory for egg production. The 170 mg tryptophan intake with 16.72 g protein was equal to control breeders with an egg production of 72 % that were consuming 235 mg tryptophan with 20.44 g protein. The researchers suggested a tryptophan intake of 192 mg day was needed for egg weight, egg mass, and body weight to be equal to control hens consuming 235 mg tryptophan in the control diet. The NRC (1994) recommendation for tryptophan for broiler breeders is 190 mg/ day. Arginine, Threonine, Isoleucine, and Valine Harms and Ivey (1992) reported the intake of arginine, threonine, isoleucine, and valine needed by breeders for equivalent egg production to control hens was 921, 605, 625, and 778 mg/day. The protein intake that provided this level of amino acid was 16.72 g/day. The control hens were consuming 20.44 g protein/day along with 1233 mg arginine, 756 mg threonine, 806 mg isoleucine, an 954 mg valine/day. The researchers reported that breeders needed 1025, 655,685, and 837 mg/day to produce the same egg mass, egg weight, and body weight compared to breeders fed control diets. The protein intake of corn-soybean diets that provided this level of amino acid was 17.51 g/day. The NRC (1994) recommendations for arginine, threonine, isoleucine, and valine for broiler breeders are 1110, 720, 850, and 750 mg day. Broiler Breeder Predicted Amino Acid Requirements Waldroup et.al.(1976) estimated the daily amino acid requirements of broiler breeders using the Model B reported by Hurwitz and Bornstein (1973). The researchers utilized a production model based on several breeder guides. Waldroup et. al.(1976) developed growth and egg production curves for different ages of breeders and the average change in body weight was calculated (Table 22). The main observation made by Leeson (1999) of the adapted data presented by Waldroup et al. is the low calculated amount of protein required by the breeders during the various stages of production. Leeson suggested in practice breeders are fed higher levels of protein as an economical way of providing the necessary amino acids. Leeson reported that most breeder flocks will be over-fed rather than under-fed crude protein because it is difficult to justify more than 23-25 g protein per day.

The maintenance requirements for laying hens that has been estimated from the models of Hurwitz and Bornstein (1973) and Smith (1978) have been estimated from the research by Leveille et al.(1960) using adult White Leghorn roosters. The extrapolation of the White Leghorn rooster maintenance requirements for broiler breeder females may not be accurate. Cave et al.(1990) reported that the maintenance requirement of TSAA for broiler breeder females determined with balance studies was three times greater per kg BW than minimum maintenance level of protein depleted White Leghorn males predicted by the model of Leveille et al. (1960). Sibbald and Wolynetz (1984) have reported that the endogenous and metabolic excretions of energy and nitrogen per unit BW.75 were greater for broiler breeders than White Leghorns. Cave et al. (1990) suggested the difference in maintenance requirements may also be related to sex differences. McDonald and Morris (1985) determined the maintenance requirement of light and medium weight laying hens was 1.6 times greater than the maintenance requirement of White Leghorn males reported by Ishibashi (1972). The broiler breeder maintenance requirements of 73 mg/kg BW/d for lysine(Gous et al., 1983), 60 mg/kg BW/d (Burnham and Gous, 1992) and 45.5 mg/kg BW/d (Huyghetaert et al., 1991) for isoleucine, and 44.4 mg/kg BW/d (Huyghetaert and Butler, 1991) for threonine either calculated at zero N-balance or by extrapolation of response curves are considered more robust than the estimated maintenance requirements of Leveille and Fisher (1960). Direct evidence is lacking comparing the accuracy of either technique. The maintenance coefficients derived from the Reading Model (Fisher et al., 1973) also have significant variations (McDonald and Morris, 1985). The a and b parameters of the Reading Model are dependent upon whether 'poor' performance hens are included or excluded in data analysis (Bowmaker and Gous, 1991). A normal distribution of the performance variables is assumed in the Reading Model (Fisher et al., 1973) which does not seem to hold for some of the performance variables for a shell egg laying flock, e.g., rate of lay and egg mass (Zhang and Coon, 1995). Bornstein et al.(1979)tested the applicability of the laying hen Models A and B for predicting the amino acid requirements of broiler breeders. The researchers completed three feeding trials with 1000 broiler breeders in each trial. The Model B was determined to support target production for the flocks significantly closer than Model A. The predicted amino acid requirements from Model A produced breeder performance in excess of the target performance. The researchers suggested the experiments verified the applicability of Model B ,developed for laying hens, for the purpose of predicting amino acid requirements for the most limiting amino acids for broiler breeders. Hurwitz and Bartov (1991) reported the predicted protein requirement from their Model B is lower than suggested by NRC(1994). The researchers suggest the model is predicting a lower protein requirement because the model requirement is an ideal amino acid mixture. The researchers noted that model diets formulated with natural ingredients were lower in dietary protein levels because of a lower predicted isoleucine requirement than suggested by NRC (1994).

Leeson and Lopez (1994) computed the amino acid requirement of two different types of breeders using the maintenance requirement estimation of Leveille et al.(1960) and tissue gain and egg production requirements from the Model B of Hurwitz and Bornstein (1973). The researchers suggested a peaking breeder can be simulated with a body weight of 2.5 kg, gaining 100 g/7 days and producing 50 g egg mass/day. The researchers suggested a 40 week-old breeder could be simulated with a 3.5 kg body weight, gaining 30 g/7 days and producing 40 g egg mass/day. The predicted requirements mainly show that the daily requirements of amino acids do not change much as the breeder ages (Table 23). Although the percent egg production declines as the breeder ages the egg size and maintenance usually increases. Leeson suggest the predicted requirements justify a one feed system because the requirements decline approximately 9.5% for the two bird types which coincides with an amino acid reduction of 11.6% when reducing feed intake from 154 g at peak production to 136 g toward the end of lay. The researchers discussed the predicted requirements from the models for the simulated breeders compared to amino acid intake of breeders fed 10% diets. The maximum protein intake for the breeders fed 10 % protein diets was only 16g/day. Lopez and Leeson (1995a) reported breeders fed 10% diets with supplemental methionine and lysine had the same overall egg production throughout a 40 week feeding period compared to breeders fed 12, 14, and 16% protein diets with equivalent lysine and TSAA levels. The breeders were fed controlled amounts of feed as specified by the breeder's management guide that increased to a maximum of 160 g/day during the 18 to 60 week period. The breeders fed the 16% protein diet reached sexual maturity earlier, had the highest peak of 89%, and also had the most persistent peak. The researchers reported the breeders fed the 16 % protein diets had a rapid decline in egg production after 45 weeks. The breeders fed 10% protein diets peaked at 85% but the group showed a better persistency toward the end of the experimental period. The breeders fed 10 % protein diets produced a total of 168 eggs compared to 166 eggs from breeders fed the 16 % diets. The breeders fed the 10% protein diets produced eggs that were approximately 3 g smaller at 30 weeks of age compared to breeders fed 16 % protein. The effect of producing smaller eggs on hatching chick weights and progeny gains was discussed by Lopez and Leeson (1995b). The smaller eggs produced by both 30 and 52 week breeders produced a 2.7 g smaller chick at 30 weeks and a 4.1 g smaller chick at 52 weeks. The final 48 day weight gain of chicks from both ages of breeders was not significantly different. The research shows that the chicks are lighter from breeders fed the 10% protein diets(160 g protein/day)but the difference in chick weight had no affect on 48 day body weights. The breeders fed the 10 % protein diets were 520 g lighter in body weight compared to breeders fed 16 % protein diets (Lopez and Leeson, 1995a). The composition of the weight gain for breeders fed 16 % diet was an average 75 g increased breast weight and 67 g increase in abdominal fat pad. The dry matter composition of the breeders fed the 16 % diet was 34.7 % protein and 58 % fat, whereas the dry matter composition of the breeders fed the 10 % protein diet was 39.4 %

protein and 50.4 % fat. The researchers discussed the feasibility of gaining weight with higher protein intakes since weight gain of breeders has been reported to be primarily related to excessive energy intake (Pearson and Herron, 1980, 1982; Wilson and Harms, 1986). Lopez and Leeson (1995) reported the breeders fed the low protein diets produced eggs that had a significantly higher hatchability than breeders fed the higher protein diets. There was no difference between groups for hatchability of fertile eggs. The breeders fed the low protein diets produced a higher percentage of fertile eggs. The researchers also noted the breeders fed the low protein diets excreted significantly less nitrogen per day. The ability to decrease the overall nitrogen waste from poultry when possible is a positive step because of increasing environmental concerns regarding waste management. Fisher (1998) recently predicted the amino acid requirements of modern day breeders using the suggested target performance goals for the Ross Breeders 308 female parent. The main components of the simple factorial equation utilized by Fisher were as follows: Raai=aE + bWn + c∆W ,where Raai= amino acid intake requirement, mg/bird/day; aE = requirement for egg production as a function of E,g egg output/d; bWn = requirement for maintenance as a function of body or tissue weight; and c∆W = requirement for tissue growth as a function of weight change. Fisher utilized the composition of eggs, body tissue, and maintenance values listed in Table 28 to predict the amino acid requirements. Fisher determined the maintenance requirements for amino acids for breeders using the following equation: MPr = BPm

-0.27. BP. X where MPr = maintenance protein requirement, g/day, expressed as ideal protein; BPm = feather-free body protein mass at maturity (=0.863 kg utilized for illustration); BP = feather-free body protein mass; and x = a constant, a value of 8 g/kg. Fisher assumed an adult breeder female would have 18% protein body composition and the gain would be 14% protein. The researcher assumed the amino acid composition of ideal protein for maintenance was the same as the amino acid composition of the body (Table 24). The amino acids required for growth were estimated by using the body protein composition with a utilization coefficient of .8 for all amino acids. Fisher’s equation for predicting amino acid requirements is for the average single bird in the breeder flock, hence, Fisher utilizes a correction for variation and adds 1.8 standard deviation in requirement to the mean to establish the flock requirements for amino acids. Fisher suggest that adding 1.8 standard deviations to the requirements will cover about 97.5% of the flock. This component is the unique feature of the Reading model that was reported by Fisher et al. (1973) for predicting amino acid requirements for laying hens. In Table 25, Fisher reports that the available lysine requirements for breeders ranges from 1080 mg/day at 28-29 weeks to a slightly lower intake requirement of 975 mg/day at the end of the laying cycle. Since the daily requirement for lysine only decreases 105 mg from peak production to the end of lay and the normal practice is to reduce feed intake and dietary energy to control body weight, Fisher suggest the percentage of lysine needed in breeder diets actually increases from .65% available lysine at peak lay to .74% available lysine at the end of lay.

The findings by Fisher are very similar to the findings of Leeson (1999) in that both investigators believe the small reduction in required amino acids per day during the laying cycle do not justify a reduction in amino acid concentration because of the decrease in feed intake. In Table 26, Fisher reports the amino acid requirements in relation to lysine for peak production at 29 weeks, at 31 weeks, and at 64 weeks. Although the amino acid profile considered to be optimum for maintenance, egg mass production, and protein gain are each different, the overall amino acid profile for the different ages of breeders does not change much. Fisher compares the predicted amino acid requirements of average individual breeders and for a flock of 27-33 week old breeders to the NRC (1994) suggested amino acid requirements (Table 27). The requirements presented by Fisher are expressed as available amino acid requirements and the NRC suggested requirements are total amino acid requirements. The predicted amino acid requirements of Fisher are generally higher than the NRC requirements. The largest difference is for lysine and histidine because Fisher utilized a larger maintenance requirement for lysine than the suggested maintenance requirement of Leveille and Fisher (1960). Fisher also shows the increase in amino acid requirements due to flock variability that were not used in some of the model calculations of Bornstein et al (1979) and Waldroup et al.(1976) in developing some of the NRC(1994) requirements. The predicted amino acids are only for the purpose of evaluating potential metabolic requirements of amino acids. The ability to model the amino acid requirement for breeders will require a better understanding of efficiency of utilization of amino acids for maintenance, weight gain, and egg mass production. The predictions are based on ideal protein mixtures that match the need of maintenance or tissue and egg gain and do not represent the actual amino acid composition needed in diets. An improvement of nutrition models will require a continuing effort to understand the actual biological use of amino acids for tissue and egg formation.

TABLES

Table 1. Ideal amino acid profile study diets.

INGREDIENT 10 – 21 d 32 – 43 d % %

Corn 78.07 67.80 Soybean meal (47%CP) 11.00 5.00

Corn oil 2.92 6.46 Defluorinated Phosphate 2.05 5.67

Limestone (Calcium Carbonate) 0.49 1.50 Vitamin & Mineral Premix 0.95 1.60

Amino Acid Mixture 4.52 11.97

nutrient analysis

Metabolizable energy, kcal/kg 3150 3302 Protein equivalents % 15.43 16.27

Table 2. Ratio of amino acids required by broilers in starter and grower periods1.

Amino Acid 10-21 d 32-43 d % of LYS % of LYS

LYS 100 100 ARG 97 101 HIS 29 31 ILE 64 62 LEU 94 117 MET 35 36 TSAA 71 69

PHE-TYR 107 102 THR 63 65 TRP 16 18 VAL 67 75

1 The levels of digestible lysine were 1.07% and 0.961 for the starter and grower diets, respectively.

Table 3. Maintenance diets.

Days of Age

10 - 21 32 - 43 Corn starch To 100% To 100%

Sucrose 15.00 17.00 Corn oil 5.50 6.50

Def. Phosphate 2.70 2.22 Limestone 1.37 0.73 Cellulose 3.00 6.00

Vit & Min Premix 2.78 2.78 Glutamic acid For 0.5% N For 1.0% N Studied AA varies varies

Nutrient analysis

CP equivalent, % 3.13 6.34 ME, kcal.kg 3500 3506

Table 4. Published data about the ideal amino acid profile for broiler chicks. * Not determined

Amino Acid

Baker 1993, 1996

NRC 1994

Austic 1994

CVB 1996

Mack 1999

0-21 d 21-42 d 0-21 d 21-42 d 0-21 d 0-42 d 20-40 d Lys 100 100 100 100 100 100 100 Met 36 36 45 38 38 38 ND* Met + Cys 72 75 82 72 72 73 75 Thr 67 70 73 74 62 65 63 Arg 105 108 114 110 96 105 112 Val 77 80 82 82 69 80 81 Ile 67 69 73 73 65 66 71 Leu 109 109 109 109 92 ND* ND* Trp 16 17 18 18 18 16 19 His 32 32 32 32 24 ND* ND*

Table 5. Partitioning the amino acid requirements for 10 to 21 day old broilers1.

1 mg/day/kg BW0.75 unless specified

Table 6. Partitioning of the amino acid requirements for 32 to 43-day old broilers1. Amino acid

Total daily requirement

Maintenance daily requirement

Maintenance as % of total

Growth requirement

Amino acid ratio to lys for growth only

Amino acid ratio to lys in broiler carcass

LYS 882 - - 882 100 100 MET 292 50 17 242 27 28 CYS 213 62 29 151 17 14 THR 550 132 24 418 48 52 TRP 157 25 22 132 15 16 ARG 875 146 17 729 83 82 VAL 670 120 18 550 62 65 LEU 967 187 19 780 88 99 ISO 576 142 25 434 49 55 PHE 389 102 26 287 32 51 TYR 294 - - 294 33 41 GLY+ SER

- - 541 61 62

PRO 504 - - 504 57 59 1 mg/day/kg BW0.75 unless specified

Amino Acid

Total daily req.

Maintenance daily requirement

Maintenance as % of total

Growth requirement

Amino acid ratio to lys for growth

Amino acid ratio to lys in broiler carcass

Lys 1003 - - 1003 100 100 Met 319 19 6 300 30 28 Cys 345 28 8 317 32 16 Thr 638 31 5 607 61 54 Trp 147 6 4 141 14 16 Arg 920 104 11 816 81 86 Val 677 36 5.3 641 64 65 Leu 1002 38 3.8 964 96 97 Ile 635 56 8.8 579 58 57 Phe 529 27 5 502 50 52 Tyr 455 20 4.4 435 43 40 Gly+Ser 927 86 9 841 84 134 His 289 4 1.4 285 28 34

Table 7. Comparison of maintenance amino acid requirements.

AA Leghorn Rooster1 Broilers2 Current Study3 mg/d/kg BW0.75 Thr 82 39 31 Val 82 32 36 TSAA 58 48 Met 22 17 Ile 73 56 Leu 81 38 Phe 19 27 Lys 0 7 0 His 0 4 Arg 81 104 Trp 10 6

1 Leveille et al, 1960

2 Emmert & Baker, 1997 and Baker et al, 1996 3 10 - 21 day old broilers

Table 8. Broiler amino acid maintenance requirements 10-21 day old 32-43 day old AA mg/d/kg BW 0.75 mg/d/kg CP mg/d mg/d/kg BW 0.75 mg/d/kg CP mg/d Met 19.44 145.04 5.03 50 213 68 Cys 28.00 217.13 7.53 62 263 84 Trp 6.27 52.19 1.81 25 110 35 Thr 30.77 256.35 8.89 132 557 178 Arg 104.16 867.65 30.09 146 517 197 Gly-Ser 86.33 720.02 24.97 Val 35.96 306.23 10.62 120 507 162 Leu 37.96 323.24 11.21 187 792 253 Ile 55.68 274.05 16.44 142 601 192 His 4.33 39.61 1.28 Phe 27.05 230.68 8.00 102 432 138 Tyr 19.7 167.82 5.82

t of 6

t of 5

t of 2

f Stil

Table 11. Amino acid composition of broiler carcass parts as affected by age Breast Thigh Drum

21d 42d 21d 42d 21d 42d % % % LYS 6.81 6.50 5.64 5.86 5.04 5.57

MET 1.98 1.96 1.69 1.93 1.53 1.68 CYS 0.94 0.89 0.82 0.88 0.79 0.83 THR 3.39 3.28 2.96 3.26 2.72 2.95 VAL 4.41 4.14 3.59 4.06 3.29 3.44 ARG 5.43 5.33 5.20 5.52 5.06 5.29 Wing Back Viscera 21d 42d 21d 42d 21d 42d % % % LYS 4.40 4.82 5.23 4.97 3.98 4.51 MET 1.40 1.33 1.43 1.51 1.38 1.27 CYS 0.80 0.67 0.82 0.76 1.04 0.96 THR 2.65 2.38 2.74 2.72 2.98 2.79 VAL 3.32 2.95 3.45 3.41 4.09 3.59 ARG 5.23 4.57 4.85 4.99 4.92 4.53

Dried, Ether Extracted Defeathered Whole Carcass Table 12. AA Carcass Content of Broilers of Two Different Ages

Amino Acid 10-21 d 32-43 d LYS MET CYS THR ARG VAL LEU ISO PHE TYR GLY-SER HIS

% 5.95 1.64 0.91 3.12 4.99 3.75 5.63 3.18 2.99 2.34 7.79 1.97

% 6.32 1.75 0.88 3.21 4.96 3.78 5.85 3.30 3.01 2.41 6.96 2.19

Dried, Ether Extracted, Whole Defeathered Carcass

Table 13. Ideal AA ratio for body weight gain, feed/gain, N accretion, AA accretion, and uric acid excretion using broken line regression analysis Amino acid

Ideal Amino Acid Ratio

Weight gain

Feed/gain Nitrogen accretion

A A accretion

uric acid

Arg 99.0 105.2 98.3 101.6 102.7 Arg* 104.9 116.9 103.6 105.2 114.4 Cys 32.1 33.8 35.2 30.4 28.2 Gly+Ser 134.5 125.3 142.1 145.4 116.9 His 33.5 37.0 37.1 38.0 31.6 Ile 77.4 76.0 81.3 83.2 77.5 Leu 123.5 126.8 138.6 138.4 131.9 Lys 100 100 100 100 100 Met 35.5 36.1 38.1 36.7 31.8 Met+Cys 67.6 69.9 73.3 67.1 60.0 Phe 63.2 65.0 66.8 67.2 64.7 Phe+Tyr 125.5 124.9 125.7 ND 128.3 Thr 75.4 70.0 73.5 74.8 64.7 Trp 19.1 19.2 19.6 20.1 19.4 Tyr 62.2 59.9 58.9 ND 63.6 Val 93.6 84.0 81.3 82.6 83.6 (%) Lys Req. 0.874 0.876 0.876 0.856 0.925 *: set Lys .1% higher than Arg % in each Arg level.

Table 14. Ideal AA ratio for body weight gain, feed/gain, N accretion, AA accretion, and uric acid excretion using exponential regression analysis Amino acid

Weight gain

A A accretion

uric acid

Arg 91.9 94.5 82.0 81.5 106.0 Arg* 100.5 106.5 83.9 83.4 135.6 Cys 28.8 29.7 29.4 27.6 41.5 Gly+Ser 141.4 101.5 104.4 103.8 96.8 His 34.3 34.8 41.2 40.9 32.5 Ile 72.3 66.3 69.7 67.6 73.9 Leu 93.8 98.7 139.6 138.8 118.3 Lys 100 100 100 100 100 Met 35.6 36.2 40.7 39.2 35.9 Met+Cys 64.5 65.9 70.1 66.8 77.4 Phe 52.7 54.2 56.4 56.1 62.3 Phe+Tyr 104.8 102.9 106.8 ND2 127.8 Thr 77.4 63.6 67.7 67.3 67.8 Trp 19.8 18.5 ND1 ND1 20.8 Tyr 52.1 48.7 50.4 ND2 65.5 Val 93.0 71.9 71.4 70.7 85.4 (%) Lys Req. 1.106 1.166 1.125 1.132 1.108 *: set Lys .1% higher than Arg % in each Arg level.

Table 15. Ideal AA ratio for body weight gain, feed/gain, N accretion, AA accretion, and uric acid excretion using polynomial regression analysis Amino acid

Weight gain

A A accretion

uric acid

Arg 113.9 117.9 104.7 103.8 114.5 Arg* 114.6 118.6 107.9 108.0 120.0 Cys 32.0 34.7 34.5 33.9 36.9 Gly+Ser 119.5 137.9 118.6 119.9 107.3 His 33.7 38.6 36.9 37.3 31.2 Ile 76.3 75.0 71.5 71.7 72.2 Leu 121.3 122.7 129.0 126.9 120.7 Lys 100 100 100 100 100 Met 43.6 44.0 44.2 44.3 49.1 Met+Cys 75.6 78.7 78.7 78.2 85.9 Phe 70.3 72.0 67.3 68.9 69.3 Phe+Tyr 127.7 139.6 123.2 ND 133.2 Thr 76.8 73.2 75.2 76.0 71.3 Trp 19.5 19.7 ND ND 18.6 Tyr 57.4 67.6 55.8 ND 63.9 Val 88.8 85.0 82.7 82.3 84.5 (%) Lys Req. 1.174 1.178 1.182 1.169 1.207 *: set Lys .1% higher than Arg % in each Arg level.

Table 16. Performance of broilers fed different diets formulated

for different AA profiles

Treatments wt gain/d (g) FCR

Uric acid (%)

N gain (g)

B. wt gain 42.511abc 1.4015bc 4.70bcd 12.223ab

B. feed/gain ratio 40.935bcd 1.4835ab 4.94bc 10.009c

P. wt gain 44.39ab 1.3612c 4.46cde 12.549a

P. feed/gain ratio 46.87a 1.3372c 3.40e 12.562a

E. wt gain 39.239cd 1.3748c 6.49a 10.489c

E. feed/gain ratio 43.015abc 1.4638ab 6.53a 10.772c

Mack’s 44.75ab 1.3424c 3.69de 12.522a

Baker’s 37.844d 1.5007a 5.59ab 10.559c

SEM 1.485 0.028 a, b, c, d Means within a column with no common superscript differ significantly.

B. wt gain: the diet formulated according to the ratio from broken-line regression analysis using wt gain as criteria

B. feed/gain ratio: the diet formulated according to the ratio from broken-line regression analysis using feed/gain as criteria

P. wt gain: the diet formulated according to the ratio from polynomial regression analysis using wt gain as criteria

P. feed/gain ratio: the diet formulated according to the ratio from polynomial regression analysis using feed/gain as criteria

E. wt gain: the diet formulated according to the ratio from exponential regression analysis using wt gain as criteria

E. feed/gain ratio: the diet formulated according to the ratio from exponential regression analysis using feed/gain as criteria

Mack’s: the diet formulated according to the ratio from Mack et al. (1999)

Baker’s: the diet formulated according to the ratio from Baker (1997)

Table 17. Daily Requirements of Digestible Amino Acids for Commercial White Layers. Amino Acid NRC Exp. 2 Exp. 3 Exp. 4 Exp. 5 Exp. 6 Ave Total1 Digestible2 (mg/d) (mg/d) (mg/g Egg Mass)3 Methionine 300 258 354 7.04 ------ ------ ------ ------ 283 5.57 3505 6.48 329 6.36 TSAA 580 499 551 11.02 ------ ------ ------ ------ 496 9.76 5955 11.00 547 10.59 Lysine 690 593 705 14.07 636 12.27 6834 12.23 ------ ------ ------ ------ 675 13.17 Arginine 700 602 968 19.52 791 15.29 ------ ------ ------ ------ ------ ------ 880 17.41 Isoleucine 650 559 603 12.07 555 10.72 ------ ------ ------ ------ ------ ------ 579 11.4 Threonine 470 404 560 11.1 430 8.43 ------ ------ ------ ------ ------ ------ 495 9.77 Tryptophan 160 138 122 2.46 ------ ------ ------ ------ 143 2.89 ------ ------ 132 2.68 Valine 700 602 731 14.19 646 12.32 ------ ------ ------ ------ ------ ------ 689 13.26

1Based on 100 grams of feed intake per day. 2NRC Amino acid digestibility based on total X 86%. 3 Amino acid requirements are based on egg mass production (includes shell). Divide mg amino acid/g

EggMass value by .911 to convert daily requirements to egg content production. 4 Average Lysine requirements based on feeding 14, 15, and 16% CP corn-soy basal diets plus an experiment using a Summit Diet:Dilution system (U.K.). 5Cao et al., 1995.

Table 18. Layer performance of four commercial strains fed experimental amino acid diets.

Diets HDEP EW EM FCHD FE ∆BWT %ALB %YLK 1. 18%CP 81.4a 62a 50.4a 94.5a 1.90a 51.1a 59.5a 27.8ab 2. 16%CP 80.5a 61.3a 49.4a 94a 1.91a -1.5b 58.9ab 28.8a 3. 16%CP+Lys 82.9a 61.6a 51a 96.6a 1.88a 2.8ab 59.6a 27.4b 4. 14%+Lys+Trp 76.8b 60.1b 46.2b 95.4a 2.07b -62.5c 58.5b 28.1ab 5. Diet 4+Ile+Val 80.2a 61.3a 49.2a 96.3a 1.96a 2.0ab 59.5a 28ab Mean 80.3 61.3 49.2 95.4 1.94 -1.64 59.2 28.03 S.D. 6.86 2.43 4.91 10.8 .224 109.6 2.71 3.16 S.E. .54 .19 .39 .86 .018 8.67 .158 .183 Crit. LSD value,.05 3.05 .81 1.91 NA .104 50.5 .89 1.12 P value .003 .0002 .0001 .82 .002 .0009 .06 .14

Table 19. Layer fourteen-day nitrogen balance study. Diets N Intake Egg N ∆Carc. N N Loss %N RET. (G) (G) (G) (G) 1. 18CP 38.14a 14.57a .205a 23.37a 38.89b 2. 16CP 34.33b 13.60ab -.216a 19.86bc 42.37ab 3. 16CP+Lys 34.40b 14.18a .019a 20.20b 41.48b 4. 14CP+Trp+Arg 30.25c 12.43b -.652a 18.33bc 39.56b 5. Diet 4+Ile+Val 30.74c 13.73a .59a 17.17c 45.94a Mean 33.54 13.70 -.01 19.87 41.57 S.D. 4.29 1.47 1.55 3.57 5.16 S.E. .62 .21 .22 .53 .76 Crit.LSD value,.05 2.94 1.19 N.A. 2.69 4.26 P value .0001 .011 .53 .0007 .022 Table 20. Ideal amino acid profile for layers Amino Acid NRC(1994) MN(1998) CVB(1996) Lysine 1.00 1.00 1.00 Methionine .434 .487 .50 TSAA .84 .81 .93 Arginine 1.01 1.30 -- Isoleucine .942 .857 .79 Threonine .681 .730 .66 Tryptophan .231 .196 .19 Valine 1.014 1.021 .86

Table 21. Breeder diet specifications for amino acids expressed per unit of protein or per unit of energy.

Breeder: Hubbard Shaver Cobb Ross Arbor Acres

Avian Hybro

Methionine (g/kg CP) 22.5 22.5 22.2 21.3 19.4 20.6 20.0 (g/Mcal) 1.26 1.39 1.20 1.19 1.09 1.17 1.24 Meth + Cys (g/kg CP) 37.4 40.6 40.0 36.3 38.8 38.8 36.5 (g/Mcal) 2.02 2.36 2.20 2.03 2.17 2.19 2.25 Lysine (g/kg CP) 45.8 46.9 48.8 50.0 51.3 46.3 44.1 (g/Mcal) 2.47 2.73 2.68 2.80 2.87 2.61 2.72 Tryptophan (g/kg CP) 10.9 10.6 10.6 11.3 10.6 11.3 9.4 (g/Mcal) 0.59 0.62 0.58 0.63 0.60 0.63 0.58

Leeson and Summers, 2000.

Table 22. Model predicted protein and amino acid needs of breeder hens. Weeks of age

CP (g/d) Amino acid (mg/hen/day)

Lysine Tryptophan Methionine Meth. + Cyst.

Threonine

22 7.2 28.2 79 258 362 320

24 7.4 282 84 275 382 335

26 9.8 400 110 341 485 428

28 13.2 608 153 450 652 580

30 15.1 742 183 530 770 690

40 15.5 722 187 552 809 695

50 14.4 625 173 528 750 650

60 13.2 542 160 495 698 600

70 12.5 497 152 480 664 570

Leeson and Summers (2000 )as adapted from Waldroup et al. (1976).

Table 23. Female broiler breeder metabolizable amino acid requirements (g/hen/day). Breeders at peak production Maintenance

(2.5 kg B. wt.) Egg Mass (50 g/d)

Growth (100 g/wk)

Total (g/day)

CYS .100 .15 .070 .32 MET .180 .21 .070 .47 THR .190 .31 .070 .57 VAL .150 .44 .110 .70 ISO .180 .40 .070 .65 LEU .310 .52 .110 .94 LYS .070 .38 .130 .58 ARG .300 .40 .110 .81 HIS .15 .030 .18 TRP .050 .08 .010 .14 PHE .150 .31 .070 .53 Breeders at 40 weeks of production

Maintenance (3.5 kg B. wt.)

Egg Mass (40 g/d)

Growth (30 g/wk)

Total (g/day)

CYS .160 .17 .020 .35 MET .240 .17 .020 .43 THR .260 .24 .020 .52 VAL .210 .36 .030 .60 ISO .250 .32 .020 .59 LEU .430 .42 .030 .88 LYS .100 .30 .040 .44 ARG .420 .32 .030 .77 HIS .10 .010 .11 TRP .070 .07 .14 PHE .210 .25 .020 .48 1 Leeson and Lopez (1994).

Table 24. Amino acid compositions utilized for estimating amino acid requirements for breeders

Body protein Egg protein Maintenance Egg A B C D ARG 6.8 6.036 50 7.387 HIS 2.6 2.228 10 2.739 i-LEU 4.0 5.420 50 6.615 LEU 7.1 8.532 32 10.375 LYS 7.5 6.768 73 8.300 MET 2.5 3.367 25 3.959 MET+CYS 3.6 6.106 60 6.889 PHE 4.0 5.110 16 6.308 PHE+TYR 7.1 9.193 32 11.205 THR 4.2 4.650 40 5.727 TRP 1.0 1.892 10 2.175 VAL 4.4 6.493 60 7.387 Derived and used in the calculations as follows: A: From summary of published data. Utilized for body protein growth with an efficiency of 0.80. Assumed composition of protein for maintenance. B: Based on amino acid composition of egg components as listed by Fisher (1994) and assuming 31.8, 57.2 and 11.0 g/100g weight and 27, 17 and 5.3 g N/kg for yolk, albumen and shell respectively. C: From Fisher (1983) based on review of available evidence. Figure used only in calculation of standard deviation of requirement. D: As for B with additional assumption that egg contains 1.89 gN/100g. Used as C. only. Fisher, 1998.

Table 25. Calculated amino acid requirements at peak-lay (29 weeks), immediately post-peak (31 weeks) and at the end of lay (64 weeks). The figures in italics for week 31 show the percentage of the total requirement accounted for by the four functions considered in the calculation. M-maintenance; E-egg production; G-body growth; F-flock variability.

Age, wk. 29 31 31 31 31 31 64 Function Total Total M E G F Total Mg per bird per day ARG 1005 929 35 45 3 17 870 HIS 376 348 36 45 3 17 325 i-LEU 767 726 26 52 2 20 661 LEU 1254 1179 29 50 2 18 1078 LYS 1121 1037 29 50 2 18 973 MET 474 448 23 56 2 20 408 MET+CYS 794 759 35 45 3 17 687 PHE+TYR 1316 1242 27 52 2 19 1130 THR 708 663 30 49 2 18 612 TRP 239 2300 21 57 2 20 205 VAL 882 838 25 54 2 19 763 Fisher, 1998.

Table 26. Calculated amino acid requirement of broiler breeders relative to lysine.

Calculated requirements (LYSINE = 100)

29 weeks of age 31 weeks of age 64 weeks of age

ARG 90 90 89

HIS 34 34 33

i-LEU 68 70 68

LEU 112 114 111

LYS 100 100 100

MET 42 43 42

MET+CYS 71 73 71

PHE+TYR 117 120 116

THR 63 64 63

TRP 21 22 21

VAL 79 81 78

Fisher, 1998. Table 27. Comparison of calculated amino acid intake requirements (available amino acids, average for weeks 27-33) with NRC (1994) recommendations (total amino acids, ‘peak’ production).

Calculated requirements NRC (1994) Average requirement mg/day Flock requirement mg/day mg/day

ARG 803 954 1110

HIS 302 357 205

i-LEU 598 734 850 LEU 988 1198 1250

LYS 893 1065 765

MET 372 453 450

MET+CYS 621 764 700

PHE+TYR 032 1259 1112

THR 558 675 720

TRP 186 230 190

VAL 693 846 750

Fisher, 1998.

FIGURES

Figure 1. Effect of dietary Met level on uric acid excreta content.

0.187 0.402 0.48 0.6 N-free 21% CP

Dig. MET %

a Uric

Figure 2. Effect of CP level in amino acid studies on broiler performance.

Glutamic acid added to increase CP level

12.86 14.65 16.43 18.21 20

Protein Equivalent, %

21 d BW, gUric Acid Body Weight

Figure 3. Effect of CP leve l in amino acid studies on broiler performance .

Glutamic acid added to increase CP level

12.86 14.65 16.43 18.21 20

Protein Equivalent, %

cid, %

43 d BW, g

Uric Acid Body Weight

Figure 4. The percentage of total whole defeathered body lysine and methionine by location and age.

Lys: 21d Lys: 42d Met: 21d Met 42d0

BreastThighDrum

REFERENCES Ambrosen, T. and S. Rotenberg, 1981. External and internal quality and chemical composition for production traits. Acta Agric. Scan. 31:139-152. Bornstein, S., S. Hurwitz, and Y. Lev, 1979. The amino acid and energy requirements of broiler breeder hens. Poultry Sci. 58:104-116. Bowmaker, J.E. and R.M. Gous, 1991. The response of broiler breeder hens to dietary lysine and methionine. Br. Poultry Sci. 32:1069-1088. Brody, T., Y. Eitan, M. Soller, I. Nir, and Z. Nitsan, 1980. Compensatory growth and sexual maturity in broiler females reared under severe food restriction from day of hatching. Br. Poultry Sci. 21:437-446. Cao, Z., H. Cai, and C. Coon, 1995. Methionine and cystine requirements and metabolism for layers and broilers. Proc. Minnesota Nutr. Conf. p257-289. Bloomington, MN Cave, N.A.G., F. Van Wambeke, and G. De Groote, 1990. Sulphur amino acid requirements of broiler breeder hens. 2. Report: Egg production. Archiv fur Geflugelkunde 54:160-166. Cave, N. A.G., F. Van Wambeke and G. De Groote, 1990. Protein and sulfur amino acid requirements of broiler breeder hens. 1. Maintenance. Archiv Geflugelkunde 54:115-119. Cotterill, O. J., W. W. Marion and E. C. Naber, 1977. A nutrient re-evaluation of shell eggs. Poultry Science 56:1927-1934. Emmans, G. C. and C. Fisher, 1986. Problems in nutritional theory. in :Nutrient Requirements of Poultry and Nutritional Research, (Ed) C. Fisher and K. N. Boorman, p9-40, Butterworths, London. Emmans, G. C., 1991. The idea behind the models. Pages 17-23 in: Proceedings of the Fortel Modelling Seminar/Workshop, London, England. Emmans, G. C., and C. Fisher, 1986. Problems in nutritional theory. Pages 9-38 in: Nutritional Requirements an Nutritional Theory. C. Fisher and K. N. Boorman, ed. Butterworths, London, England. Fisher, C., T. R. Morris, and R. C. Jennings, 1973. A model for the description and prediction of the response of laying hens to amino acid intake. British Poultry Science 14: 469-484. Fisher, C., 1998. Amino acid requirements of broiler breeders. Poultry Sci. 77:124-133.

Harms, R.H., 1992. A determination of the order of limitation of amino acids in a broiler breeder diet. J.Appl. Poultry Res. 1:410-414. Harms, R.H. and E.J. Ivey, 1992. An evaluation of the protein and lysine requirement for broiler breeder hens. J. Appl. Poultry Res. 1:308-314. Harms, R. H. and H. R. Wilson, 1980. Protein and sulfur amino acid requirements of broiler breeder hens. Poultry Sci. 59:470-472. Hocking, P. M. and A. B. Gilbert, 1985. The effects of energy restriction on growth and ovarian function in broiler breeders. Brit. J. Poultry Sci.27:154-162. Hrubý, M., M. L. Hamre, and C. N. Coon, 1995. Broiler performance under free-choice feeding and three temperature treatments. J Applied Poultry Res. (In Press) Hrubý, M., M. L. Hamre, K. L. Leske, and C. N. Coon, 1995. The effect of age on utilization of digestible amino acids for broilers under free-choice feeding. Poultry Sci. 74: Supplement 1. p122. (abstract) Hurwitz, S. and S. Bornstein, 1973. The protein and amino acid requirements of laying hens: suggested model calculations. Poultry Sci. 52:1124-1134. Hurwitz, S. and I. Bartov, 1991. Modeling of the energy and amino acid requirements of broiler breeders. Proc. Arkansas Nutr. Conf., p55-65. North Little Rock, Ark. Ishibashi, T., 1972. Amino acid requirements for maintenance of the adult rooster. Jap. J. Zootechnical Sci. 44:39-49. Johnson, R. J., R. B. Cumming and D. J. Farrell, 1985. Influence of food restriction during rearing on the body composition of layer-strain pullets and hens. British Poultry Science 26:335-348. Katanbaf, M. N., E. A. Dunnington, and P. B. Siegel, 1989. Restricted feeding in early and late-feathering chickens. Poultry Science 68:359-368. Kirchgessner, M. and Steinhart, H., 1981. Arch. Geflugelk. 45:179. Kuana, S., P. R. Soares, H. H. S. Rostagno, M. de Almeida e Silva, and J. B. Fonseca, 1988. The metabolizable energy and methionine plus cystine requirement in broiler breeder hens. Revista da Sociedade Brasileira Zootecnia 17:385-392. Leeson, S., 1999. Protein nutrition of broiler breeders. Simposio International Sobre Nutricao de Aves. Campinas, SP-Brazil. WPSA-Brazilian Branch. Leeson, S. and G. Lopez, 1994. Protein nutrition of broiler breeders. Proc. Arkansas Nutr. Conf.,p248-255. Fayetteville, Ark. Leveille, G.A., R. Shapiro and H. Fisher, 1960. Amino acid requirements for maintenance in the adult rooster. J.Nutr. 72:8-15.

Leveille, G. A., and H. Fisher, 1960. The amino acid requirements for maintenance in the adult rooster. J. Nutr. 72:8-15. Lopez, G. and S. Leeson, 1994. Nutrition and broiler performance: a review with emphasis on response to diet protein. J. Appl. Poultry Res. 3:303-311. Lopez, G. and S. Leeson, 1995. Response of broiler breeders to low-protein diets. 1. adult breeder performance. Poultry Sci. 74:685-695. Lopez, G. and S. Leeson, 1995. Response of broiler breeders to low-protein diets. 2. offspring performance. Poultry Sci. 74:696-701. Lopez, G., and S. Leeson, 1994. Response of older broiler breeders to medium-high intakes of protein. J. Appl. Poultry Res. 3:157-163. Lunven, P., Le Clement de St Marcq, C., Carnovale, E. and Fratoni, A., 1973. Amino acid composition of hen's egg. British J. of Nutrition. 30:189-194. McDonald, M. W. and T. R. Morris, 1985. Quantitative review of optimum amino acid intakes for young laying pullets. Brit. J. Poultry Sci.26:253-264. Morris, T. R. and R. M. Gous, 1988. Partitioning of the response to protein between egg number and egg weight. Brit. J. Poultry Sci. 29:93-99. National Research Council, 1994. Nutrient Requirements of Poultry. Ninth revised edition. National Acad. Sci., Washington, D.C. Pearson, R.A. and K.M. Herron, 1980. Feeding standards during lay and reproductive performance of broiler breeders. Br. Poultry Sci. 21:171-181. Pearson R.A. K. M. Herron, 1982. Relationship between energy and protein intakes and laying characteristics in individually-caged broiler breeder hens. Br. Poultry Sci. 23:145-159. Sibbald, I. R. and M. S. Wolynetz, 1984. A longitudinal study of energy and nitrogen excretion by fasted cockerels. Poultry Sci. 63:691-702. Smith, W. K., 1978a. The amino acid requirements of laying hens: models for calculation. 1. physiological background. World's Poultry Sci.34:81-96. Smith, W. K., 1978b. The amino acid requirements of laying hens: models for calculation. 2. practical application. World's Poultry Sci. 34:129-136. Soares, R., S. Kuana, H.S. Rostagno, M.S. Silva, and J.B. Fonseca, 1988. Nutritional requirement for lysine in broiler breeder hens. Revista da Sociedade Brasileira Zootecnia 17:393-400. Talpaz,H., J.R. De La Torre, P. J. H. Sharpe, and S. Hurwitz, 1986. Dynamic optimization model for feeding of broilers. Agr. Systems 20:121-132.

Waldroup, P.W., Z. Johnson, and W. Bussell, 1976. Estimating daily nutrient requirements for broiler breeder hens. Feedstuffs 48 (28):19. Wilson, H. R. and R. H. Harms, 1984. Evaluation of nutrient specifications for broiler breeders. Poultry Sci. 63:1400-1406. Wilson, H. R., and R.H. Harms, 1986. Performance of broiler breeders as affected by body weight during the breeding season. Poultry Sci. 65:1052-1057. Zhang, Bingfan and C. N. Coon, 1995. The distribution of performance variables in laying hens and implication of feed formulation. Poultry Sci. 74: Supplement 1. p12 (abstract)

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