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

14 August 2004

By Craig Coon, Poultry Science Department, University of Arkansas and published by the American Soybean Association - 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.

The Ideal Amino Acid Requirements and Profile for Broilers, Layers, and Broiler Breeders - By Craig Coon, Poultry Science Department, University of Arkansas and published by the American Soybean Association - 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.

American Soybean Association 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.


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.

To read the full report, please click here (PDF)

Source: The American Soybean Association - July 2004

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