Amino Acid Considerations for Modern Broilers

Digestible amino acids and ratios to lysine are used extensively in formulating diets for poultry (broilers, layers, turkeys, ducks, quail, etc.) on a global basis. Amino acid use has and will continue to increase in the coming decades, especially as high priced ingredients, more limited resources and the environmental impact of excessive dietary nitrogen come more into consideration through life-cycle assessments (McGill et al., 2012, Kidd et al., 2013). The digestible lysine (dLys) level of the diet, for each stage of production, is critical in setting the minimums for the other essential digestible amino acids, as they are defined as ratios relative to dLys. This formulation method is widely employed as it simplifies the least-cost process since a change in overall amino acid density only requires an alteration in the dLys level. An increase or decrease in amino acid density is often employed when significant changes are observed in either feed and/or meat prices; however, having a sound scientific basis for the degree of change in dLys, versus just an arbitrary adjustment, is critical in order to maximize profitability. As high priced ingredients, more limited resources and the environmental impact of excessive dietary nitrogen

Several review papers, covering recent broiler amino acid research have been published (Tillman, 2011a, Tillman, 2012 and Tillman and Dozier, 2013). This paper, which is the 4th consecutive update on this topic, includes a thorough bibliography and set of tables, and picks up from the previous three papers by providing an updated review of digestible amino acid requirements and ratios to dLys through inclusion of the most recently published or presented information. Some additional emphasis will be placed upon digestible methionine (dMet) and digestible sulphur amino acids (dSAA: digestible methionine plus digestible cysteine) as they were not covered in the first two review(s). Recent research on the other key essential digestible amino acids, which have the potential to be most deficient in typical broiler diets: Lysine, Threonine (dThr), Valine (dVal), Isoleucine (dIle), Tryptophan (dTrp) and Arginine (dArg) will be updated. Then, in summary some economic concepts for optimizing the dLys level for maximum profitability will be discussed. 

Sriperm (2011^a,b) evaluated the dLys level which would maximize bird performance, as well as the use of various models using the dLys level which would maximize economic return and profitability. The profitability portion of this will be discussed in more detail in the economic section towards the end of this paper. A central composite rotatable design was employed evaluating a titration of the dLys level during the grower (15-35d) as well as the finisher (early:35-42d or late:35- 49d) phase. It was noted that during the grower phase, the dLys level which maximized bodyweight gain, feed conversion and either breast meat weight or yield were, 1.126, 1.388 and 1.135%, respectively, averaging 1.196%. During the 15-42d growout, which encompassed both the grower and early finisher periods, the optimal dLys levels for the grower and early finisher respectively were : 1.113 & 0.996% for bodyweight gain, 1.125 & 0.997% for liveweight, 1.135 & 0.994% for carcass weight, 1.182 & 0.981% for breast meat weight and 1.404 & 0.920% for breast meat yield. On average, these were 1.192% during the grower phase and 0.978% during the early finisher phase to day 42. For the longer growout (15-49d), encompassing both the grower and late finisher periods, the optimal dLys levels for the grower and late finisher respectively were: 1.081 & 0.972% for bodyweight gain, 1.098 & 0.992% for liveweight, 1.094 & 0.988% for carcass weight, 1.094 & 0.995% for breast meat weight and 1.089 & 1.004% for breast meat yield. On average, these were 1.091% during the grower phase and 0.990% during the late finisher phase to day 49. It should be noted that the average dLys level for the grower and early finisher (35-42d) phases were 1.192% and 0.978%, respectively; however, the average dLys level for the grower and late finisher (35-49d) phases were 1.091%and 0.990%, respectively. The longer grow out decreased the optimal dLys level during the grower (15-35d) phase, but increased the optimal dLys level during the finisher phase, despite the birds grown for an additional 7 days. In conclusion, it was noted that the dLys which maximized performance (growth and processing) depended to some degree upon the length of the growout period.

Dozier and Payne (2012) determined the dLys requirement of broilers from 1 to 15 days of age in two experiments. The first trial, during October of 2009, used 1,600 Ross x Ross 708 females and the second trial, during September of 2010, used Hubbard x Cobb 500 female broilers. Corn, soybean meal, peanut meal (10.14%) and poultry by-product meal (5%) diets were fed. Digestible lysine was titrated in each trial from 0.95% to 1.43% in 0.08% increments, so as to create 7 treatment diets. In experiment 1, using quadratic broken-line analysis, the dLys requirement, from 1 to 7 days of age, was shown to be 1.352 and 1.383 for bodyweight gain and feed conversion, respectively. In experiment 2, also using quadratic broken-line analysis, the dLys requirement, from 1 to 7 days of age, was shown to be 1.265 for bodyweight gain. Analysis of the dLys requirement from 1 to 14 days of age in trial 1 indicated a quadratic broken-line breakpoint at 1.27 for bodyweight gain; whereas in trial 2, it was shown to be 1.18 for bodyweight gain and 1.261 for feed conversion. It was concluded that these requirement estimates were higher than previous recommendations and research attributable to some degree to the improved feed conversion of these birds.

Nasr & Kheiri (2012) in a 2x3 factorial design with 2 means of formulation (using total versus digestible amino acids) and with 3 planes of Lys nutrition (-10% of NRC, NRC and +10% of NRC). Male broilers from 1-42d were used across 30 floor pens, providing 6 replicates per treatment. It was noted that diets based upon digestible amino acids had significantly greater breast percentage versus the alternative method of formulation. In addition, the higher plane of Lys nutrition also yielded both greater carcass (+4.4%) and breast (+1.81%) percentages than the diets with lower levels of Lys. The diet with the highest dLys level provided significantly higher carcass, breast and thigh weights versus the other 9 treatments.

Oliveira et al. (2013) reported on the lysine requirement of 8 to 21 day of age broilers using an all-vegetable Corn-Soybean meal based diet. A 5x2 factorial design was used with five levels of dLys and 2 methods of formulating (only using Corn, soybean Meal and added methionine (CSM) versus balancing with numerous industrial amino acids (IAA)). Typical responses to graded levels of dLys were noted for lysine intake, body weight gain, fat deposition, feed conversion and protein deposition. In the CSM and IAA diets, the dLys levels of 1.30 & 1.40% were deemed to provide optimum performance, respectively. The CSM diet estimate of 1.30% for the optimum dLys for bodyweight gain was determined using the quadratic maximum, whereas feed conversion optimum was determined to be 1.28% using the linear broken-line model. The IAA estimate for dLys was really not determinable using any break-point analysis and the reported 1.40% estimate was based upon the highest level actually fed – as the response was essentially linear.

Siqueira et al. (2013) examined the dLys requirement of Cobb 500 male broilers from 1-8d and 8-22d using either the diet dilution or the diet supplementation method. A 5x2 factorial design was used with five points of dLys and the two formulation methods noted above. Six replicates were used for each point with each replicate pen having 20 birds each. In the starter (1-8d) phase, dLys levels from 0.975 to 1.403 were used, incremented by 0.107. In the grower (8-22d) phase, dLys levels from 0.840 to 1.208 were used, incremented by 0.092. Using the feed conversion response from the diet dilution technique, which was viewed as superior to the diet supplementation approach, the estimated dLys requirements determined as the quadratic maximum were reported to be 1.361 and 1.187, for the two phases respectively. 

Methionine is the first limiting amino acid for broilers fed corn-soybean meal diets and sulfur amino acids are used for lean tissue accretion, feather formation, and methyl donation (Garcia and Batal. 2005). Sulfur amino acid (SAA) requirements of broilers have been estimated from 0 to 3 weeks of age (National Research Council. 1994; Lumpkins et al., 2007), but data are limited with digestible SAA (dSAA) to Lys ratios for the starting chick. The dSAA to Lys ratio has been reported as 72 from 8 to 22 d of age (Baker and Han, 1994) while Knowles and Southern (1998) reported the dSAA to Lys ratio at 66 and 63 for BW gain and feed efficiency.

Kalinowski et. al. (2003) reported that the total methionine requirement in 0 to 3 week old broiler chicks was 0.50%, regardless as to whether they were slow or fast feathering strains. However, it was noted that the Cysteine requirement was 0.39% for slow-feathering males versus 0.44% for fast-feathering males. These values would predict a SAA requirement of between 0.89% and 0.94% for the 0 to 3 week of age broiler, depending upon feathering rate.

Rubin et al. (2007) examined the effects of both methionine and arginine dietary levels on the immunity of broiler chickens submitted to immunological stimuli. They noted that Met has four primary functions: 1) protein synthesis, 2) glutathione precursor, 3) synthesis of polyamines and 4) methyl donation.

Bunchasak (2009) wrote a review on the role of Met in poultry production. It was noted that Met supplementation improves the immune response through both direct and indirect effects. Direct effects were noted as protein synthesis while indirect effects were noted through compounds produced from methionine, such as homocysteine, glutathione and taurine. As such, methionine deficiency can lead to both humoral and nonspecific cellular immunocompetencies. It was noted relative to the requirement that it is higher than the NRC (1994), decreases with age, but increases with age when expressed as a ratio to lysine.

Geraert and Mercier (2010) discussed the role of amino acids beyond those of protein synthesis. In their discussion, two of the areas which were highlighted were immunity and antioxidant activity, particularly the role of Met and SAA in these areas. Methionine had been shown to improve the immune status of birds via increased antibody production. It was also noted that the conversion of methionine into either glutathione or taurine were both cited as having positive impacts upon reducing oxidative stress.

Goulart et al. (2011) reported on the dSAA ratio of Cobb male broilers from 1 to 42 days of age. Four phases were evaluated: pre-starter (1-7d), starter (8-21d), grower (22-35d) and finisher (36- 42d). It was determined that the dSAA requirement was 0.873%, 0.755%, 0.748% and 0.661%, corresponding to dSAA/dLys ratios of 71, 70, 76 and 72%.

In a recent study, Dozier et al. (2013a) and Dozier and Mercier (2013) examined the dSAA ratio to Lys in Hubbard × Cobb male broilers from 1 to 14 days of age. Eight concentrations of dSAA/dLys were fed ranging from 0.56 to 0.86% in increments of 0.06%. Diets were formulated to contain 1.16% dLys. Digestible SAA/dLys ratio was determined to be 78 and 77 from 1 to 7 and 1 to 14 days of age, which is higher than requirements estimated from previous research.

Rostagno et al. (2011) has reported a dSAA to Lys ratio of 72 for 1 to 21 day old broilers.

Research conducted with the modern broiler having market weights from 2.0 to 3.0 kg is sparse (Baker at al., 1996). Furthermore, these studies determined an absolute requirement and not the total SAA ratio to Lys. The dSAA to Lys ratio has been reported as 75 from 20 to 40 days of age (Mack et al., 1999). Moreover, Rostagno et al. (2011) estimated the dSAA to Lys ratio as 73 for 21 to 56 day old broilers.

Mehri et. al. (2012) examined the ideal ratios for both methionine and threonine to lysine, of Ross x Ross 308 male broiler chicks, from day 3 to day 16. Response surface methodology was employed using a central composite rotatable design. Bodyweight gain was maximized when dLys was 1.12% and dMet was 0.54%, corresponding to a dMet/dLys ratio of 48. Similar requirement optimums were noted for feed conversion with dLys at 1.13% and dMet at 0.53%, corresponding to ideal ratios for dMet/dLys of 47.

Dozier et al. (2013b) examined the dSAA to Lys ratio of Ross × Ross 708 male broilers from 42 to 56 days of age. Broilers were fed 9 experimental diets consisting of 8 concentrations of dSAA/dLys ratios ranging from 0.60 to 0.88 in increments of 0.04. A standardized Lys digestibility assay was conducted with broiler chicks to determine amino acid digestibility of the basal diet. Standardized dSAA of the basal diet was determined to be 0.53%. Progressive additions of dSAA/dLys resulted in a significant linear effects for breast meat weight (P = 0.057) and yield (P = 0.035), but no treatment differences were observed for growth performance. Digestible SAA/dLys ratios were estimated at 76 and 74 for total breast meat weight and yield. These data indicated that dSAA/dLys ratios for modern broilers are higher for total breast meat yield than growth performance. 

Neto et al. (2012) determined the dThr/dLys ratio in Male Cobb 500 broilers from 1-7d. Typical Corn, Soybean, Meat & Bone Meal (5%) and Wheat Bran (4%) diets were using in creating the basal and summit diets. Diets were formulated at 95% of the Brazilian Tables (Rostagno et al., 2005). Five points on the titration curve from a dThr/dLys ratio of 50 to 75, with increments of ~ 6 were used. Quadratic maximum was used as the determinant for the ideal ratio. While the typical performance measurement of bodyweight and bodyweight gain gave an estimated dThr/dLys ratio of 65, other measurements (fat content (%), fat deposition (g) and crude protein / fat content ratio gave estimates between 68 & 69. The overall conclusion was that a ratio of 68 resulted in the best performance and body composition.

Brito et al. (2013) reported on the dTHR requirement in 1-7d and 8-21d of age male and female (straight-run) Ross 508 broilers. For bodyweight gain during the 1-7d phase, using either the linear broken line (LBL) or the Quadratic maximum (Qmax) model, the dThr requirement estimate was 0.77 and 0.79%, respectively. During the 8-21d phase, the estimated dThr requirements were 0.67 and 0.71% from the LBL and Qmax models, respectively. Other variables measured did not exhibit a significant response to increasing levels of dThr. While the LB model gave lower error terms, it is generally considered that this model under-estimates the requirement (Morris, 1983).

From the published paper by Mehri et. al. (2012) noted above, both the ideal ratios for methionine and threonine to lysine were examined in 3 to 16 day old broilers. Bodyweight gain was maximized when dLys was 1.12% and dThr was 0.78%, corresponding to a dThr/dLys ratio of 70. Similar requirement optimums were noted for feed conversion with dLys at 1.13% and dThr at 0.75% of the diet, corresponding to an ideal ratio of dThr/dLys of 66.

Star et. al. (2012) looking at the threonine requirement of Ross 308 male broiler chickens from either day 9 to 20 or day 9 to 27 in three experiments. A subclinical infection model was employed at days 9 and 14 by inoculation with Eimeria maxima and Clostridium perfringens. While lesion incidence, lesion severity or mortality were not impacted by the dThr/dLys ratio, there were responses noted in body weight gain and feed intake with increased dThr/dLys ratios of 69 and 67, respectively. It was also noted in trial 3 that infected birds had improved bodyweight gain and feed intake when provided a dThr/dLys ratio of 67 versus one of only 63, which was also noted to carryover out to day 37. It was concluded that while an increased dThr/dLys ratio did not improve intestinal damage from a subclinical E. maxima and C. perfringens inoculation, there were noted improvements in bodyweight gain and feed intake. In addition, linear broken-line analysis of gain per feed from experiments 1 & 2 generated a break-point at a 68 dThr/dLys ratio.

Duarte et al. (2012) examined the dThr requirement of 22 to 42 day of age male Cobb broilers. Six dThr levels were used and a level of dThr of 0.7642% was determined to be the requirement using a linear broken line model. It should be noted that while dThr/dLys ratio of 71.19 was reported, this trial design was not setup to determine a ratio. The dLYS level used, of 1.0735% was essentially at or above the requirement for these 22-42d old broilers and it is imperative in ratio work that the dLys level be set below the requirement.

Mejia et al. (2012^a) evaluated the dThr/dLys ratio of Ross 708 male broilers from 35-49 days of age, using simultaneous dLys and dThr titrations. A range from 0.70% to 1.15% for dLys and of 0.40% to 0.85% for dThr were used in the determination of the optimal ratio. For BW gain, optimal dLys was 1.09% and optimal dThr was 0.72%, yielding a dThr/dLys ratio of 66. Absolute requirements for dThr were shown to be 0.67%, 0.72% and 0.74% for feed consumption, FC and breast meat weight, respectively. The dThr for maximum breast weight, put against the dLys for maximum bodyweight gain would yield a 68 ratio for dThr/dLys.

Meloche et al, (2013) presented on the dThr/dLys ratio in 1-14 days of age Hubbard x Cobb 500 male broilers. Eight titration diets were used with dThr as a % of the diet ranging from 0.62 to 0.86%. The dLys level of the treatment diets was set below the requirement at 1.13% and each treatment was replicated across 8 pens. The titration of the dThr/dLys ratio ranged from 55 to 76. Linear broken line analysis was used as an estimate of the optimal ratio, although it is known that this is not ideal for representing a population and tends to underestimate the requirement. The optimal dThr/dLys ratio was determined to be 70 and 68 for bodyweight gain and feed conversion, respectively. It was concluded that a minimum ratio of 68 was required.

Wecke & Liebert (2013) published in the open access, non-peer reviewed journal on a new, although yet un-validated approach to determining individual amino acid ratios. The need for further validation of this approach was noted by Pastor et al. (2013). Using nitrogen balance experiments, along with nitrogen deposition and retention determinants, the slope (also noted as the efficiency parameter) of a linear line from a control diet (adequate in all amino acid levels) was used against the slope of a linear line from a diluted diet (deficient in the test amino acid) as a means of calculating a ratio. Three trials, using thirty-five birds in each were raised in metabolism cages with either 5 or 7 birds per experimental diet. Two ages were examined (11-21d) and (25-35d) for total amino acid ratios for Thr, Trp, Arg, Ile and Val. Several data points were omitted from the final conclusion based upon the slope of the nitrogen retention curve being non-significant and an average across the three trials were reported, sometimes being represented by only one trial. Reported total amino acid ratios for Trp (19 & 17) and Arg (105) were somewhat similar to those reported in the literature for digestible ratios while the reported ratios for Thr, Ile and Val, tended to be significantly lower than those reported digestible ratios. It should be noted however that a comparison between total and digestible ratio can be difficult to make.

Jiang et al. (2014) reported on the dThr/dLys ratio for Hubbard M99 x Cobb 500 male broilers from 21 to 35 days of age. Eight titration diets were used with dThr as a % of the diet ranging from 0.49 to 0.77%. The dLys level of the treatment diets was set below the requirement at 0.95% and each treatment was replicated across 8 pens. The titration of the dThr/dLys ratio ranged from 51.2 to 80.6. Quadratic broken line analysis was used to estimate the optimal dThr/dLys ratio and it was determined to be 68 and 67 for bodyweight gain and feed conversion, respectively. It was concluded that this study pointed to the dThr/dLys ratio being higher than previously published for the particular age range evaluated. 

Corzo et al. (2010) examined requirement estimates for dVal and dIle in corn, SBM, meat & bone meal based diets fed to Ross TP16 male broilers from day 28 to day 42. A PC diet was formulated to be adequate in all nutrients, while a negative control diet was formulated to be deficient in both dVal and dIle. The control diets were formulated at 0.99% dLys with the PC having 0.75% dVal and 0.66% dIle and the negative control (NC) diets being 0.10% points lower for both of these AA. This in effect dropped the ratio of dVal/dLys from 75 to 65 and that of dIle/dLys from 66 to 56 across the two control diets. Six additional treatment diets were created by adding L-Val and/or L-Ile back to the NC diet such that either 50% or 100% of the differences for dVal and/or dIle were recovered. There was a significant decline in performance in both BW gain and feed intake when the dVal and dIle levels were decreased from the PC to NC diets. Bodyweight was recoverable when either L-Val alone or in combination with L-Ile were added back to the negative control diet. Feed conversion required both added L-Val and added L-Ile to show improvement. As had been reported before, breast meat yield responded to supplemental L-Ile (Kidd et al., 2000). It was deemed that in these diets, containing meat & bone meal, that live performance responded more to dVal and was fourth limiting; whereas dIle supplementation increased breast meat yield more. As such, a scenario of co-limitation likely existed between these two essential AA in regards to optimizing growth and meat yield.

Corzo et al. (2011) reported on a practical trial designed to evaluate the inclusion of L-Val in diets fed to Ross TP16 broilers from 28 to 42 days of age. Two control diets were formulated to meet all nutrient requirements. A positive control (PC) diet contained added DL-Methionine, L-Lys HCl and L-Thr and served as the dilution diet in the dVal titration, while an industry control (IC) diet contained these AA plus L-Val at 0.034% and represented a potential diet of the future. A summit diet was formulated using 0.13% added L-Val and was blended in various proportions with the PC diet to make four intermediate titration diets, with added L-Val in increments of 0.026%. The summit diet was formulated to maintain a 78 ratio between dVal and dLys, while allowing the ratios on dIle, dArg and dTrp to drop as SBM was replaced with added L-Val. No differences in performance or processing variables measured existed between the PC & IC diets, indicating L-Val could be least cost formulated into a diet at 0.034%, successfully. Results from the titration of L-Val inclusion suggested that up to 0.052% L-Val is feasible in practical diets without significantly sacrificing bird performance or processing measurements.

Dozier et al (2012) examined the interactive effects of dVal and dIle to dLys ratios to male Ross x Ross 708 male broilers from either 28 to 42d of age (trial 1) or from 26 to 40d of age (trial 2). Trial 1 used 10 experimental diets consisting of a positive control diet (1.0% dLys) and a 3 x 3 factorial arrangement of dVal/dLys ratio (74, 78 or 82) and dIle/dLys ratio (63, 68 and 73) ) with a reduced dLys level (0.95%). Trial 2 was similar to Trial 1 in that it also used a 3 x 3 factorial arrangement of dVal/dLys ratio (74, 78 and 82) and dIle/dLys (62, 67 and 72) at a reduced dLys level (0.92%); however, two control diets were fed – one at the dLys requirement (1.02%) and the other at a reduced dLys level (0.92%). These were included to assure that dLys was slightly deficient in the treatments, by comparing the two controls, as well as to compare back to the treatment diet with similar dLys, dVal and dIle levels. In experiment one, a slightly significant (p=0.045) dVal/dIle ratio interaction was noted for feed conversion and mortality. No significant main effects for broiler performance or carcass characteristics were noted however, indicating that perhaps the 74 dVal/dLys ratio was adequate. In experiment 2, no interactions were noted and the main effects of dVal ratio to dLys were significant for bodyweight, bodyweight gain, feed conversion and abdominal fat which were optimized at a dVal/dLys ratio of 82. Interestingly enough however, was the response in breast meat yield which was also significant being maximized at the lowest dVal/dLys ratio.

Tavernari et al, (2013) determined the optimal dVal/dLys ratio in Male Cobb 500 (fast feathering) broilers between 8 & 21d (Starter) and between 30 and 43d (Finisher) of age. Appropriately, the dLys level of the all-vegetable based treatment diets was reduced below the requirement, in this case by 7%. Six titration points of dVal/dLys were used in each of the phases. In the Starter these ranged from 69 to 84 while in the Finisher phase the ranged from 70 to 85, in both cases being incremented by 3 ratio points. For the Starter phase, the dVal/dLys ratio for bodyweight gain, using 95% of Qmax and the LBL was shown to be 77 and 79, respectively. The feed conversion ratio was optimized at a dVal/dLys ratio of 75 and 76 using 95% of Qmax and the LBL model, respectively. For the finisher phase, 95% of Qmax model gave a dVal/dLys ratio of 75and 77, for bodyweight gain and feed conversion, respectively and 75 and 74, when using the LBL model.

Berres et al. (2011), using male Cobb 500 broilers, studied the dVal requirement, as a % of the diet from 21 to 42 days of age. An all-vegetable, corn-soybean based diet was used throughout and seven points on the titration curve were used, with dVal ranging from 0.71 to 0.97%, based upon analysis. The range of dVal levels was achieved through the use of added L-Val with all other ingredients being kept constant. Results were analysed using 95% of Qmax as well as the LBL model to determine the dVal requirement and since dLys was set at 1.10%, this was not designed to be a ratio trial although ratios of 77 and 76 were reported for bodyweight gain and feed conversion. Results from using 95% of the Qmax indicated that the dVal requirement, as a % of the diet, was 0.85, 0.84 and 0.85% for bodyweight gain, feed conversion and abdominal fat pad yield, respectively. The LBL model predicted the dVal requirement for bodyweight gain, feed conversion and abdominal fat pad yield to be 0.82, 0.81 and 0.73, respectively. Other measured variables did not show a significant response to dVal titration, as often observed for the first three limiting amino acids in broiler feeds (SAA, LYS and THR).

Campos et al (2012) examined the ideal amino acid ratios for arginine, isoleucine, valine and tryptophan in male broilers from 7-21 and from 28-40d. The dLYS used for each phase (1.08 & 0.98%) were set below the requirement while all other nutrients (except for dVal) were at or above the requirement, since this was a ratio trial. Three points on the curve were used for the dVal / dLys ratio for the two phases : 70, 75 and 80 and 71.5, 77, 82.5, respectively. The dVal / dLys ratios used during the 7-21d phase showed linear responses for bodyweight gain and feed conversion. The optimal dIle / dLys ratio for the 28-40d phase was deemed to be 76.

From a review of recent publications, it appears evident that dVal is clearly fourth limiting in all vegetable based broiler feeds with corn and/or wheat as the primary grain source (Tillman, 2011, Tavernari et al, (2013)). 

Dozier et al. (2011) reported on the results from a trial designed identically to Corzo et al. (2010), except for the use of poultry by-product meal rather than meat and bone meal. The greatest breast meat responses in weight or yield tended to occur at the highest dIle levels, but often in conjunction with additional L-Val. It was deemed that in these diets, dIle was likely fourth limiting, although it was closely followed by dVal, again implying a scenario of co-limitation between these two essential AA. These two trials, point to the importance of setting proper ratios or levels for both dVal and dIle.

Mejia et al. (2011) evaluated the dIle/dLys ratio of Ross 708 male broilers from 28 to 42 days of age. A PC diet was formulated at 1.00% dLys and set to be adequate in all essential amino acids, including dIle, with a ratio of 67. Two treatment diets were formulated at 0.95% dLys, which is slightly below the requirement, to have either a dIle/dLys ratio of 57.8 or 74.4, representing the basal and summit titration treatment diets, respectively. These two dies were blended so as to create 5 intermediate diets across the 7 point titration curve. It was concluded a ratio of 68.9 was adequate for live performance and that a ratio of 71.7 gave similar results in regards to breast meat yield as to the PC diet, even though the latter was ~ 2.25 percentage points higher in CP. These results support the possibility of there being a higher dIle/dLys ratio requirement to maximize breast meat responses.

As described in the dVal section above, Dozier et al. (2012) examined the interactive effects of dVal and dIle in two trials, using Ross x Ross 708 males. In experiment 1, the main effects indicated that increasing the ratio of dIle to dLys reduced abdominal fat weight while increasing breast meat yield (at least up to 68). There was no significant impact on broiler growth parameters from increasing the dIle/dLys ratio in either trial 1 or 2. As in trial 1, results from trial 2 indicated a significant response to increasing the dIle/dLys ratio in terms of improving breast meat yield (at least up to 67).

Tavernari et al (2012) evaluated the dIle / dLys ratio in male Cobb 500 broilers from 7-21 and from 30-43 days of age. A titration range from 58 to 75.3, incremented by 3.5 points providing 6 treatment levels. Diets were based upon Corn, soybean meal, corn gluten meal and spray-dried plasma. Results were reported as linear broken line (break-point), Qmax (within the Figures) and also as 95% of Qmax and Quadratic broken-line (QBL) (both within the text). As such, a close reading of the paper is required to fully extract the results. As the LBL typically underestimates the optimal ratio, I will discuss here the Qmax, 95% of Qmax and QBL – although the LBL results are also shown in Table 6. During the 7-21d period, the following Qmax, 95% of Qmax and QBL values respectively were reported as : 68, 65, 64 for bodyweight gain, 69, 66, 65 for feed conversion, breast weight and breast fillet weight and 70, 67, 66 for breast yield and breast fillet yield. During the 30- 43d period, the following Qmax, 95% of Qmax and QBL values respectively were reported as : 70, 66, 64 for feed intake, 72, 68, 68 for bodyweight gain and 75, 72, 72 for feed conversion. It was concluded overall that the dIle / dLys ratio recommendation was 66 from 7-21d and 68 from 3-43d.

Campos et al (2012) examined the ideal amino acid ratios for arginine, isoleucine, valine and tryptophan in male broilers from 7-21 and from 28-40d. The dLYS used for each phase (1.08 & 0.98%) were set below the requirement while all other nutrients (except for dIle) were at or above the requirement, since this was a ratio trial. Three points on the curve were used for the dIle / dLys ratio, for the two phases : 60, 65, 70 and 58, 67, 76, respectively. The dIle / dLys ratios used during the 7- 21d phase showed linear responses for bodyweight gain and feed conversion. The optimal dIle / dLys ratio for the 28-40d phase was deemed to be 69. 

Hsia et al. (2005) evaluated the effect of tryptophan on growth and carcass characteristics in Hubbard male broilers in a series of three trials and across various ages. Trial 1 was conducted from 35-56d of age, trial 2 from 21-49d of age and trial 3 from 14-42d of age. Levels of total tryptophan fed in the three trials were: trial 1- 0.198%, 0.228% and 0.258%, trial 2- 0.167% or 0.198% and trial 3- 0.136%, 0.167% and 0.198%. The total lysine level content was 1.1%, 1.0% and 1.0% for trials 1, 2 and 3, respectively. In trial 1, no differences were noted between the three treatments for feed intake, bodyweight gain, feed conversion or carcass characteristics. It was noted in trial 2 feed intake was not different between the two treatment levels; however bodyweight gain, feed conversion and a few of the carcass characteristics were significantly different in the high versus low total tryptophan level fed. In trial 3, the lowest level of tryptophan fed gave the lowest bodyweight gain and poorest feed conversion. In addition, the lowest total tryptophan level fed also gave the poorest weights for breast, thigh and heart.

Corzo (2012) evaluated the arginine and tryptophan ideal ratios in Ross x Ross 708 male and female broilers from 1 to 18 days of age. No differences were noted between the two sexes. For dTrp, five points across the titration curve were used ranging from 10 to 22 in increments of 3 ratio points. A value of 95% of the quadratic maximum response was used as the estimate for the ideal ratio. The determined ideal ratios for bodyweight gain, feed intake and feed conversion were 18, 19 and 17, respectively. On average, the ideal ratio for dTrp/dLys was 18.

Campos et al (2012) examined the ideal amino acid ratios for arginine, isoleucine, valine and tryptophan in male broilers from 7-21 and from 28-40d. The dLYS used for each phase (1.08 & 0.98%) were set below the requirement while all other nutrients (except for dTrp) were at or above the requirement, since this was a ratio trial. Three points on the curve were used for the dTrp / dLys ratio, for the two phases : 15, 16, 17 and 14, 17, 20, respectively. No responses were observed from the dTrp treatments during the 7-21d phase. The optimal dIle / dLys ratio for the 28-40d phase was deemed to be 76.

The order of limitation for tryptophan and arginine should generally fall after those for dVal and dIle. The ratio for tryptophan tends to be in the range of 16 to 18 and rarely is a constraint, even though it should be monitored, particularly in diets containing high levels of corn plus corn distillers dried grains with solubles. 

As noted above, Corzo (2012) evaluated the arginine and tryptophan ideal ratios in Ross x Ross 708 straight-run broilers from 1 to 18 days of age. No differences were noted between the two sexes. For dArg, five points across the titration curve were used ranging from 75 to 115 in increments of 10 ratio points. As before, a value of 95% of the quadratic maximum response was used as the estimate for the ideal ratio. The determined ideal ratios for bodyweight gain, feed intake, feed conversion and livability were 108, 106, 114 and 103, respectively. On average, the ideal ratio for dArg/dLys was determined to be108.

Mejia et. al. (2012) evaluated the dArg/dLys ratio of male Ross 708 broilers from 28 to 42 days of age during a constant, elevated temperature. Corn, soybean meal, corn distiller dried grains with solubles, meat & bone meal based diets were used. Digestible arginine was titrated, using LArg, across 7 treatment diets from a ratio of 100 to 130, relative to dLys which was set below the requirement at 0.95%. Based upon performance and processing responses, it was determined that the dArg/dLys ratio was no higher than 105. It was concluded from this paper that dArg typically should not become a formulation constraint unless sorghum/milo is the primary grain source in the diet. Nonetheless, it is proper and advisable to set a minimum dArg/dLys ratio of at least 105 and perhaps upwards of 108 in later phase diets, although it naturally increases across phases.

Campos et al (2012) examined the ideal amino acid ratios for arginine, isoleucine, valine and tryptophan in male broilers from 7-21 and from 28-40d. The dLYS used for each phase (1.08 & 0.98%) were set below the requirement while all other nutrients (except for dArg) were at or above the requirement, since this was a ratio trial. Three points on the curve were used for the dArg / dLys ratio, for the two phases : 100, 105, 110 and 95, 105, 115, respectively. No responses were observed from the dTrp treatments during the 7-21d phase. The dArg / dLys ratios used during the 28-40d phase showed linear responses for bodyweight gain and feed conversion.

Neto et al. (2013) examined the dArg/dLys ratio in Cobb 500 male broilers from 21 to 42 days of age under high environmental temperature. While they only examined a 105 and 140 ratio of dArg/dLys, they noted that broilers provided the 105 ratio had better live performance, carcass weights, carcass yields, longer villi length and shallower crypt depths. In addition, when the birds were innoculated with an antigen, the lower dArg/dLys ratio gave a better immune response. 

Several papers have addressed the impact of amino acid levels on optimizing profitability (DeBeer (2009, 2010), Eits et al. (2005 a,b), Lemme (2005), Pack et al. (2003), Ziggers (2011)). Due to the extensive use of ideal amino acid ratios in formulation, most of the emphasis has been placed upon the economically optimal dLys level; however, Kidd et al. (1998) noted the optimal level of dThr which maximized profitability was near the dThr level which also maximized broiler performance (feed conversion) and processing (carcass composition) parameters. It is likely that this is the case for all of the essential amino acids – that feeding near their requirement for performance is also close to the point which maximizes profitability. Afterall, improvements in bodyweight gain, feed conversion and carcass characteristics (particularly breast meat weight and yield) are often noted for several of these amino acids.

Sriperm (2011^a,b) evaluated various models to determine the economically optimal dLys level which would maximize profitability from selling whole carcass or parts. These scenarios were evaluated across a wide range of both feed ingredient (dietary) costs as well as meat (carcass, breast, wings and leg quarters) prices. For example, one example evaluated Corn at ~$280/ton and Soybean Meal at ~ $385/ton prices, along with the carcass price at ~ $0.64/pound price, the optimal dLys level to maximize profitability was 1.09% during the grower (15-35d) and 0.90% during the late finisher (35-49d), using a Cobb-Douglas production function. These values are not dissimilar to those determined from the static : production approach cited above. If carcass price were higher than that noted above, then the optimal dLys level for profitability would increase and it was noted that the meat or carcass price was more of a driver for the optimal profitability than is feed price.

Tillman and Sriperm (2011^b) presented a paper looking at the difference between dLys requirements determined from static : production (growth and feed efficiency) estimates versus those determined from profitability which also incorporates dynamic : market process (feed costs and meat prices). Various prediction models were employed, including the line intercept of models, the dLys requirement for static : production variables were determined using an average value from a quadratic broken-line (QBL) model, a quadratic and linear two-slope broken line model, the intercept of the linear broken-line model and quadratic polynomial model and the intercept of the QBL and quadratic polynomial model. It was shown that the requirement for Cobb 700 males from 28-42d were 0.95%, 0.99%, 1.00% and 0.97% for bodyweight gain, feed conversion, carcass weight and breast meat weight, respectively. These average of these static : production dLys requirements was 0.978%. When dynamic : market assessment of the dLys requirement which optimizes profitability was determined, across a wide range of feed and meat prices, the results were similar for the point which was the best case scenario (low feed but high meat prices). For example, the dLys level which maximized profitability for the carcass at the best case scenario was 0.986% and that for maximizing profitability from the breast meat was 0.980%. What was of particular note however was the worst case scenario for each example, which only reduced the dLys level for maximum profitability by 0.889% and 0.947% for carcass and breast meat return, respectively. These differences from best to worst case only decreased the dLys level for maximum profitability by 0.097 and 0.033 percentage points, respectively. These value differences are less than what is sometimes done within the broiler industry, based upon what is “felt” to be the correct decision – thus pointing out the importance of making well informed decisions when it comes to overall amino acid density of broiler diets.

Abstracts of presentations are available from Perryman et al. (2013, Trial 1) and Tillman et al. (2013, Trial 2) with Ross x Ross 708 male broilers grown to 42 days of age and Hubbard M99 x Cobb 500 male broilers grown to 35 days of age, respectively. Five treatments were offered ranging from a basal to a summit diets, with intermediates labelled as industry low, industry high and requirement diets. For the Ross broilers, weighted dLys levels, based upon dietary dLys level and feed intake, from 0.86% to 1.14% in increments of 0.07 percentage points were fed across the three phases (starter: 1-14, grower: 15-28 and finisher: 29-42). In both trials, linear responses in carcass weight, carcass yield, breast weight, breast yield, drumstick weight, wing weight and thigh weight were noted to increasing dLys levels and intakes. Quadratic responses were also noted for carcass weight, breast weight and breast yield in trial 1, but only for drumstick, wing and thigh weights in trial 2. A weighted average dLys level of 1.07%, was determined as the point where return over feed cost was maximized after 42 days of growth with the Ross 708. For the second paper presented, using Hubbard M99 x Cobb 500 male broilers, grown to 35 days of age, the weighted dLys level ranged from 0.88% to 1.16%, again in increments of 0.07 percentage points. A weighted average dLys level of 1.02%, was determined as the point where return over feed cost was maximized after 35 days of growth with the Hubbard M99 x Cobb 500 male broiler. 

This paper has strived to provide an update on AA broiler nutrition during the past few years, with special emphasis on the dLys, dThr, dVal, dIle and dArg requirements and more particularly the dThr/dLys, dVal/dLys, dIle/dLys and dArg/dLys ratio recommendations. With the enhancements in growth rates, FC and white meat yields, largely due to genetic selection, AA requirements have become critical to maximize technical performance while optimizing economic performance. The ratio on the next limiting AA, which cannot be supplemented, becomes highly critical in maintaining a proper nitrogen pool from which non-essential amino acids and proteins can be synthesized. Depending upon the ingredients used and the commercial AA’s economically available, this next limiting AA can vary. Therefore, special emphasis needs to be placed on setting proper ideal ratios for these potentially limiting essential AA’s (dVal, dIle, dArg and dTrp) which are also required to optimize broiler performance and profitability. 

Table 1. Digestible Lysine Requirements

 Table 2. Digestible Methionine / dLys Ideal Ratio Recommendations

 Table 3. Digestible SAA / dLys Ideal Ratio Recommendations

 Table 4. Digestible Threonine / dLys Ideal Ratio Recommendations

 Table 5. Digestible Valine / dLys Ideal Ratio Recommendations

 Table 6. Digestible Isoleucine / dLys Ideal Ratio Recommendations

 Table 7. Digestible Tryptophan / dLys Ideal Ratio Recommendations

Table 8. Digestible Arginine / dLys Ideal Ratio Recommendations

 Table 9. Recommendations for Broiler Ideal Digestible Amino Acid Ratios relative to Digestible Lysine

Baker, D. H., S. R. Fernandez, and D. M. Webel. 1996. Sulfur amino acid requirement and cysteine replacement value of broiler chicks during the period three to six weeks posthatching. Poult. Sci. 75:737-742.

Baker, D. H. and Y. Han. 1994. Ideal amino acid profile for chicks during the first weeks posthatching. Poult. Sci. 73:1441-1447.

Berres, J., S.L. Vieira, W.A. Dozier III, M.E.M. Cortes, R. de Barros, E.T. Nogueira and M. Kutschenko. 2010. Broiler responses to reduced-protein diets supplemented with valine, isoleucine, glycine and glutamic acid. Journal of Applied Poultry Science 19:68-79.

Berres, J., S.L. Vieira, A. Favero, D.M. Freitas, J.E.M. Pena and E.T. Nogueira. 2011. Digestible valine requirements in high protein diets for broilers from twenty-one to forty-two days of age. Animal Feed Sci, and Technology 165:120-124.

Brito, A., J.H. Stringhini, R.M.J. Filho, S.A.G. Xavier, M.B. Café and N.S.M. Leandro. 2013. Protein and Digestible Threonine Levels in Pre Starter Diets for Broiler Chicks. Int. Journal of Poultry Science 12 (7):406-410.

Bunchasak, C. 2009. Role of Dietary Methionine in Poultry Production. Japan Poult. Sci. 46: 169- 179.

Campos, A., E.T. Nogueira, L.F. Albino and H. Rostagno. 2009a. Effects of digestible isoleucine :lysine ratios on broiler performance and breast yield. Poultry Science Annual Meeting. Poster 351. Raleigh, NC.

Campos, A., E.T. Nogueira, L.F. Albino and H. Rostagno. 2009b. Digestible valine : lysine ratios for broilers during the starter and finisher periods. Poultry Science Annual Meeting. Poster 352. Raleigh, NC.

Campos, A., H.S. Rostagno, E.T. Nogueira, L.F.T. Albino, J.P.L. Pereira and R.C. Maia. 2012. Updating of the ideal protein for broilers: arginine, isoleucine, valine and tryptophan. Revista Brasileira de Zootecnia 41 (2):326-332.

Corzo, A. 2012. Determination of the arginine, tryptophan, and glycine ideal-protein ratios in high-yield broiler chicks. Journal of Applied Poultry Research 21:79-87.

Corzo, A., W.A. Dozier III, and M.T. Kidd. 2008a. Valine nutrient recommendations for Ross X Ross 308 broilers. Poultry Science. 51 (4) 558-563.

Corzo, A., W.A. Dozier III, M.T. Kidd and D. Hoehler. 2008b. Impact of dietary isoleucine on heavy-broiler production. International Journal of Poultry Science. 7 (6) 526-529.

Corzo, A., W.A. Dozier III, R.E. Loar II, M.T. Kidd and P.B. Tillman. 2009a. Assessing the threonine-to-lysine ratio of female broilers from 14 to 28 days of age. Journal of Applied Poultry Research 18:237-243.

Corzo, A., W.A. Dozier III, R.E. Loar II, M.T. Kidd and P.B. Tillman. 2010. Dietary limitation of isoleucine and valine in diets based on maize, soybean meal and meat-and-bone meal for broilers. British Poultry Science. 51 (4) 558-563.

Corzo, A., W.A. Dozier III, L. Mejia, C.D. Zumwalt, M.T. Kidd and P.B. Tillman. 2011. Nutritional feasibility of L-valine inclusion in commercial broiler diets. Journal of Applied Poultry Science. 20:284-290.

Corzo, A., M.T. Kidd, W.A. Dozier III and S.L. Vieira. 2007. Marginality and needs of dietary valine for broilers fed certain all-vegetable diets. Journal of Applied Poultry Research 16:546- 554.

Corzo, A., R.E. Loar and M.T. Kidd. 2009b. Limitations of dietary isoleucine and valine in broiler chick diets. Poultry Science 88:1934-1938.

Corzo, A., E. T. Moran Jr and D. Hoehler. 2004a. Isoleucine need of heavy broiler males. Arch. Geflugelk 68 (5) 194-198.

Corzo, A., E. T. Moran Jr, and D. Hohler. 2004b. Valine needs of male broilers from 42 to 56 days of age. Poultry Science 83:946-951.

Costa, F.G.P., S.A.N. Morais, E.T. Nogueira, M. Kutschenko, C.C. Goulart, R.C.L. Neto, C.F.S. Oliveira, V.P. Rodrigues and M.R. Lima. 2010a. Digestible valine:digestible lysine ratio for broilers in the growing phase. International Poultry Scientific Forum. Abstract P241.

Costa, F. Guilherme Perrazzo, S. Antonio de Normando Moraes, E. Terra Nogueira, M. Kutschenko, C. Castro Goulart, M. Ramalho de Lima, C. Franklin Santos de Oliveira, R. Cunha Lima Neto, G. Bruno Vieira Lobato and I. Souza Nobre. 2010b. DVal:dLys ratio for broiler chickens in the final phase. Proceedings from the XIIIth European Poultry Conference. Tours, France. August 23-27th. http://www.epc2010.org/

De Beer, M. 2009. Adjusting nutrient density when faced with volatile markets. Arkansas Nutrition Conference. September. Rogers, Arkansas.

De Beer, M. 2010. Nutrition for maximum profit – Do the math. Aviagen Brief. October. 5 pages.

Dimova, M.D., R.B. Shirley, J.L. Usry, P.B. Tillman, M.E. Freeman and A.J. Davis. 2010. The digestible lysine requirement of Cobb 500 x Hubbard M99 male broilers from 35 to 49 days of age. Poultry Science Association Annual Meeting. Denver, CO. Nonruminant Nutrition – AA 1 Abstract and Oral presentation 138. Submitted for publication.

Dozier III, W.A., A. Corzo, M.T. Kidd, P.B. Tillman and S.L. Branton. 2009a. Digestible lysine requirements of male and female broilers from fourteen to twenty-eight days of age. Poultry Science 88:1676-1682.

Dozier III, W.A., A. Corzo, M.T. Kidd, P.B. Tillman, J.P. McMurtry and S.L. Branton. 2010a. Digestible lysine requirements of male broilers from 28 to 42 days of age. Poultry Sci. 89: 2173-2182.

Dozier III, W.A., A. Corzo, M.T. Kidd, P.B. Tillman, J.L. Purswell and B.J. Kerr. 2009b. Dietary lysine requirement of male broilers from 14 to 28 days of age subjected to different environmental conditions. Journal of Applied Poultry Research 18:690-698.

Dozier III, W.A., A. Corzo, R.E. Loar II, M.T. Kidd and P.B. Tillman. 2011. Determination of the fourth and fifth limiting amino acids in broilers fed on diets containing maize, soybean meal and poultry by-product meal from 28 to 42 d of age. British Poultry Science. 52 (2) 238-244.

Dozier, W. A., III and Y. Mercier. 2013a. Digestible total sulfur amino acids to lysine ratio of broiler chicks from 1 to 15 days of age. Journal of Applied Poultry Research 22:862-871.

Dozier, W. A., III and Y. Mercier. 2013b. Digestible total sulfur amino acid to lysine ratio of male broilers from forty-two to fifty-six days of age. Poultry Science Association Annual Meeting, San Diego, CA, Oral Presentation.

Dozier III, W.A., R.L. Payne. 2012. Digestible lysine requirement of female broilers from 14 to 28 days of age. Journal of Applied Poultry Research 21:348-357.

Dozier III, W.A., P.B. Tillman and J. Usry. 2012. Interactive effects of digestible valine and isoleucine-to-lysine ratios provided to male broilers from 4 to 6 weeks of age. Journal of Applied Poultry Research 21:838-848.

Duarte, K.F., O.M. Jungueira, R.S. Filardi, J.C. Siqueira, E.A. Garcia and A.C. Laurentiz. 2012. Threonine requirements of 22-42 days-old broilers. Revista Brasileira de Zootecnia 41 (1):72- 79.

Eits, R.M., R.P. Kwakkel, M.W.A. Verstegen, and L.A. Den Hartog. 2005a. Dietary balanced protein in broiler chickens. 1. A flexible and practical tool to predict dose-response curves. British Poultry Science. 46, 3. 300-309.

Eits, R.M., G.W.G. Giesen, R.P. Kwakkel, M.W.A. Verstegen, and L.A. Den Hartog. 2005b. Dietary balanced protein in broiler chickens. 1. An Economic Analysis. British Poultry Science. 46, 3. 310-317.

Everett, D.L., A. Corzo, W.A. Dozier III, P.B. Tillman and M.T. Kidd. 2010. Lysine and threonine responses in Ross TP16 male broilers. Journal of Applied Poultry Research 19:321-326.

Garcia, A. and A. B. Batal. 2005. Changes in the digestible lysine and sulfur amino acid needs of broiler chicks during the first three weeks posthatching. Poult. Sci. 84:1350-1355.

Geraert, PA and Y Mercier. 2010. Amino Acids: Beyond the building blocks. Arkansas Nutrition Conference Proceedings.

Goodgame, S., C. Coto, F. Mussini, C. Lu, A. Karimi, J. Yuan and P. Waldroup. 2011. The potential role of valine in commercial poultry diets. International Poultry Scientific Forum. Abstract P217. Page 30

Goulart, C. de Castro., F.G.P. Costa, J.H.V. de Souza, V.P. Rodrigues, C.L.S. de Oliveira. 2011. Requirements of digestible methionine+cystine for broiler chickens at 1 to 42 days of age. R. Bras. Zootec., c.40, n.4., 797-803.

Hale, L.L., S.J. Barber, A. Corzo and M.T. Kidd. 2004a. Isoleucine needs of thirty to forty two day old female chickens: Growth and carcass responses. Poultry Science 83:1986-1991.

Hale, L.L., G.T. Pharr, S.C. Burgess, A. Corzo and M.T. Kidd. 2004b. Isoleucine needs of thirty to forty two day old female chickens: Immunity. Poultry Science 83:1979-1985.

Helmbrecht, A., F. de Castro Tavernari, H.S. Rostagno, L.F. Teixeira Albino and A. Lemme. 2010. Optimal digestible isoleucine to lysine ratios in starter and finisher broilers. Proceedings from the XIIIth European Poultry Conference. Tours, France. August 23-27th. http://www.epc2010.org/

Hsia, L.C., J.H. Hsu and C.T. Liao. 2012. The effect of varying levels of tryptophan on growth performance and carcass characteristics of growing and finishing broilers. Asian-Aust. J. Anim. Sci. 18 (2) 230-234.

Jiang, Z, W.A. Dozier and P.B. Tillman. 2014. Digestible Thr to Lys ratio of male broilers from 21 to 35 days of age. International Poultry Scientific Forum, Atlanta, GA, January. Metabolism & Nutrition VI Abstract and Oral presentation T138.

Kalinowski, A., E.T. Moran and C. Wyatt. 2003. Methionine and cystine requirements of slowand fast-feathering male broilers from zero to three weeks of age. Poultry Science 82:1423- 1427.

Kidd, M.T. 2000. Nutritional considerations concerning threonine in broilers. World’s Poultry Science Journal. 56 (2) 139-151.

Kidd, M.T., D.J. Burnham and B.J. Kerr. 2004. Dietary isoleucine responses in male broiler chickens. British Poultry Science. 44 (1) 67-75.

Kidd, M.T., W.A. Dozier III, P.B. Tillman, R.E. Loar II, and A. Corzo. 2010. Dietary addition of L-Valine for commercial broilers. International Poultry Scientific Forum, Atlanta, GA, January. Nutrition V Abstract and Oral presentation T123.

Kidd, M.T. and L. Hackenhaar. 2005. Dietary threonine for broilers: dietary interactions and feed additive supplement use. CAB Reviews 1: No 005.

Kidd, M.T., B.J. Kerr, J.P. Allard, S.K. Rao and J.T. Halley. 2000. Limiting amino acid responses in commercial broilers. Journal of Applied Poultry Research 9:223-233.

Kidd, M.T., S.P. Lerner, J.P. Allard, S.K. Rao and J.T. Halley. 1999. Threonine needs of finishing broilers: Growth, carcass and economic responses. Journal of Applied Poultry Research 8 (2) 160-169.

Kidd, M.T. and P.B. Tillman. 2012. Feed Additive Mythbusters: How Should we Feed Synthetic Amino Acids? February 23. Proceedings of Ajinomoto Animal Nutrition Technical Seminar. Amino Acid Nutrition in Broiler Diets. Pages 57-64. Bangkok, Thailand.

Kidd, M.T., P.B. Tillman, P.W.Waldroup and W. Holder. 2013. Feed-grade amino acid use in the United States: The synergistic inclusion history with linear programming. Journal of Applied Poultry Research 22:583-590.

Knowles, T. A. and L. L. Southern. 1998. The lysine requirement and ratio of total sulfur amino acids to lysine for chicks fed adequate or inadequate lysine. Poult. Sci. 77:564-569.

Lemme, Andreas. 2005. Optimum dietary amino acid levels for broiler chicken from proceedings of the II International Symposium on Nutritional Requirements of Poultry and Swine. Editors: Horacio Santiago Rostagno and Luiz Fernando Teixeira Albino, held in Vicosa, MG, Brazil. March 29-31. Pages 117-143.

Lumpkins, B. S., A. B. Batal, and D. H. Baker. 2007. Variations in the digestible sulfur amino acid requirement of broiler chickens due to sex, growth criteria, rearing environment, and processing yield characteristics. Poult. Sci. 83:1307-1313.

Mack, S. D. Bercovici, G. de Groote, B. Leclercq, M. Lippens, M. Pack, J. B. Schutte, and S. Van Cauwenberghe. 1999. Ideal amino acid profile and dietary lysine specification for broiler chickens of 20 to 40 days of age. Br. Poult. Sci. 40:257-265.

Maia, R.C., S.C. Saiguero, T.A. Carvalho, E.T. Nogueira, L.F.T. Albino and H.S. Rostagno. 2012. Effect of normal and high dietary levels of isoleucine, Leucine and valine on performance of broiler chickens from 14-23 days of age. World’s Poultry Science Journal, Supplement 1, Expanded Abstract – Poster Presentation. Worlds Poultry Congress – Bahia, Brazil August 5-9.

Mehri, A., A. Davarpanah and H.R. Mirzaei. 2012. Estimation of ideal ratios of methionine and threonine to lysine in starting broiler chicks using response surface methodology. Poultry Science 91:771-777.

Meloche, K.J., P.B. Tillman and W.A. Dozier III. 2013. Growth performance of male broilers fed diets varying in digestible threonine from 1 to 14 days of age. International Poultry Scientific Forum, Atlanta, GA, January. Metabolism & Nutrition I Abstract and Oral presentation M27.

Mejia, L., D. Morgan, P. Tillman, W. Zhai. 2013. Increased amino acid density, reduced metabolizable energy and inclusion of L-Threonine maximizes performance and profitability in Ross X Ross 708 male broilers. International Poultry Scientific Forum, Atlanta, GA, January. Metabolism & Nutrition II Abstract and Oral presentation M62.

Mejia, L., P.B. Tillman, C.D. Zumwalt and A. Corzo. 2012. Assessment of the threonine-to-lysine ratio of male broilers from 35 to 49 days-of-age. Journal of Applied Poultry Science. 21:235-242.

Mejia, L., C.D. Zumwalt, E.J. Kim, P.B. Tillman and A. Corzo. 2011.. Digestible isoleucine-to-lysine ratio effects in diets for broilers from 4- to 6-weeks posthatch. Journal of Applied Poultry Science. 20:485-490.

Mejia, L., C.D. Zumwalt, P.B. Tillman, R.B. Shirley and A. Corzo. 2012. Assessment of the digestible arginine-to-digestible lysine ratio of male broilers from 28 to 42 days-of-age a constant, elevated environmental temperature regimen. Journal of Applied Poultry Science. 21:305-310.

Meloche, K., P. Tillman, W. Dozier III. 2013. Growth performance of male broilers fed diets varying in digestible threonine from 1 to 14 days of age. . International Poultry Scientific Forum, Atlanta, GA, January. Metabolism & Nutrition I Abstract and Oral presentation M27.

McGill, E., A. Kamyab and J.D. Firman. 2012. Low Crude Protein Corn and Soybean Meal Diets with Amino Acid Supplementation for Broilers in the Starter Period 1. Effects of Feeding 15% Crude Protein. Int. Journal of Poultry Science 11 (3):161-165.

Morris, T.R. 1983. The Interpretation of Response Data from Animal Feeding Trials in Recent Advances in Animal Nutrition. Chapter 1. Pages 1-11.

Nasr, J., F. Kheri. 2012. Effects of Lysine Levels of Diets Formulated Based on Total or Digestible Amino Acids on Broiler Carcass Composition. Brazilian J. of Poult. Sci. Oct-Dec. v.14 n.4 233-304.

Neto, R.C.L., F.G.P. Costa, R.L. Furlan, P.E.N. Givisiez, C.C. Goulart, C.F.S. Oliveira, S.A.N. Morais, R.M. Bezerra and M.R. Lima. 2012. Levels of digestible threonine for male broilers from 1 to 7 days of age. Journal of Applied Poultry Research 21:757-763.

Neto, R.M., M.L. Ceccantini and J.I.M. Fernandes. 2013. Effects of methionine source, arginine:lysine ratio and sodium chloride level in the diets of grower broilers reared under hightemperature conditions. Brazilian J. of Poult. Sci. Apr-Jun. v.15 n.2 151-160.

NRC. 1994. Nutrient Requirements of Poultry. 9th ed. Natl. Acad. Press, Washington, DC. Oliveira, W.P, R.F.M

Oliveira, J.P. Donzele, L.F.T. Albino, P.H.R.F. Campos, E.M. Balbino, A.P. Maia and S.M. Pastora. 2013. Lysine levels in diets for broilers from 8 to 21 days of age. Revista Brasileira de Zootecnia 42 (12):869-878.

Pack, M., D. Hoehler and A, Lemme. 2003. Economic assessment of amino acid responses in growing poultry, in Amino Acids in Animal Nutrition. 2nd edition. J.P.F. D’Mello Editor. CABI Publishing, Wallingford, UK. Pages 459-483.

Pastor, A., C. Wecke and F. Liebert. 2013. Assessing the age-dependent optimal dietary branchedchain amino acid ratio in growing chickens by application of a nonlinear modeling procedure. Poultry Science 92:3184-3195.

Perryman, K., P. Tillman, W. Dozier III. 2013. Increased dietary amino acid density from 1 to 42 d of age optimizes profitability in Ross X Ross 708 male broilers. International Poultry Scientific Forum, Atlanta, GA, January. Metabolism & Nutrition I Abstract and Oral presentation M29.

Rodehutscord, M., A.A. Fatufe. 2005. Protein and valine gain of broilers in response to supplemental L-Valine. Proceedings of the 15th European Symposium on Poultry Nutrition, World's Poultry Science Association. Balatonfüred, Hungary. September 25-29. 545-547.

Rostagno, H.S., Albino, L.F.T., Donzele, J. L., Gomes, P.C., de Olveira, R.F., Lopes, D.C., Firiera, A.S., and Barreto, S.L. de T., 2005. Brazilian Tables for Poultry and Swine. Composition of Feedstuffs and Nutritional Requirements. 2nd ed. H. S. Rostagno, ed. Universidade Federal de Vicosa, Dept. Zootecnia, Vicosa, MG, Brazil.

Rostagno, H.S., L.F.T. Albino, J.L. Donzele, P.C. Gomes, R. Flavia de Olveira, Lopes, A.S. Ferreira, S.L de Toledo Barreto and R.F. Euclides. 2011. Brazilian Tables for Poultry and Swine. Composition of Feedstuffs and Nutritional Requirements. 3rd ed. H. S. Rostagno, ed. Universidade Federal de Vicosa, Dept. Zootecnia, Vicosa, MG, Brazil.

Rostagno, H., L Pae’z and L. Albino. 2007. Nutrient requirements for broilers for optimum growth and lean mass. World’s Poultry Science Association. XVI European Symposium Poultry Nutrition. Strasbourg, France.

Rubin, L.L., C.W. Canal, A.L.M. Ribeiro, A. Kessler, I. Silva, L. Trevizan, T. Viola, M. Raber, T.A. Gonalves and R. Kras. 2007. Effects of methionine and arginine dietary levels on the immunity of broiler chickens submitted to immunological stimuli. Brazilian J. of Poult. Sci. Oct-Dec. v.9 n.4 241-247.

Rubin, L.L., A.M.L. Ribeiro, C.W. Canal, I.C. Silva, L. Trevizan, L.K. Vogt, R.A. Pereira and L. Lacerda. 2007. Influence of sulphur amino acid levels in diets of broiler chickens submitted to immune stress. Brazilian J. of Poult. Sci. Oct-Dec. v.9 n.1 53-59.

Shirley, R.B., J.L. Usry and P.B. Tillman. 2009. The digestible lysine requirement of fastfeathering, straight-run, 35 to 45 day-old Cobb x Cobb 500 broilers. International Poultry Scientific Forum, Atlanta, GA, January. Nutrition III Abstract and Oral presentation M67.

Siqueira, J.C., N.K. Sakomura, L.R.B. Dourado, J.M.B. Ezequiel, N.A.A. Barbosa and J.B.K. Fernandes. 2013. Diet formulation techniques and lysine requirements of 1-22 day-old broilers. Brazilian J. of Poult. Sci. Apr-Jun. v.15 n.2 123-134.

Sriperm. 2011a. Optimal broiler production via nutrition. Agricultural Economics Masters thesis. University of Georgia. Athens, GA. 63 pages. Sriperm, N. 2011b. Protein and amino acid content of feed ingredients and the impact of dietary balanced protein on maximizing economic returns from broiler technical responses. Poultry Science Doctoral dissertation. University of Georgia. Athens, GA. 174 pages.

Sriperm, N., P.B. Tillman, G.M. Pesti and M.E. Wetzstein. 2008. An economic analysis of LThreonine in a broiler grower diet, using a least-cost model, based upon digestible amino acids and ideal digestible amino acid ratios. Poultry Science Association Annual Meeting. Niagara Falls, Canada.

Star, L., M. Rovers, E. Corrent and J.D. van der Klis. 2012. Threonine requirement of broiler chickens during subclinical intestinal Clostridium infection. Poultry Science 91 : 643-652

Tavernari, F.C., G.R. Lelis, P.R.O Carneiro, R.A. Vieira, R.C. Polveiro, J.A.P. Luengas, H.S. Rostagno and L.F.T. Albino.. 2012. Effect of different digestible isoleucine/lysine ratios for broiler chickens. Revista Brasileira de Zootecnia 41 (7):1699-1705.

Tavernari, F.C., G.R. Lelis, R.A. Vieira, H.S. Rostagno, L.F.T. Albino and A.R. Oliveira Neto. 2013. Valine needs in starting and growing Cobb (500) broilers. Poultry Science 92:151-157.

Thornton, S.A., A. Corzo, G.T. Pharr, W.A. Dozier III, D.M. Miles and M.T. Kidd. 2006. Valine requirements for immune and growth responses in broilers from 3 to 6 weeks of age. British Poultry Science 47 (2) April. 190-199.

Tillman, P.B. Reducing broiler feed cost with L-Threonine. 19th Annual Philsan Convention, 2006. “Cutting-Edge” Nutrition: A Challenge to Animal Nutritionists. October 6th. Cebu City, Philippines.

Tillman, P.B. 2007. Practical application of L-Threonine in broiler nutrition Proceedings of the Arkansas Nutrition Conference. September 12th Rogers, Arkansas.

Tillman, P.B. Amino acid nutrition and incorporating L-Threonine in broiler formulas. 2008 Proceedings of the Mid-Atlantic Nutrition Conference. March 27th. Timonium, MD.

Tillman, P.B. 2010a. An update on amino acid requirements for broilers and layers. (Actualización de la nutrición con aminoacididos para pollos y gallina de postura). XXI Congreso Centroamericano y del Caribe de Avicultura. San Jose, Costa Rica. June 16-18.

Tillman, P.B. 2010b. Improving environmental sustainability of poultry production with amino acids. Proceeding of the Multi-State Poultry Feeding and Nutrition Conference. Session C : Environmental Nutrition. Indianapolis, IN. May 25th-27th.

Tillman, P.B. 2011a. Special Considerations for Amino Acids in Broiler Nutrition. III International Symposium on Nutritional Requirements of Poultry and Swine. March 29-31. Pages 21-44. Vicosa, Brazil.

Tillman, P.B. 2012. Current Amino Acid Considerations for Broiler Diets : Requirements, Ratios, Economics. February 23. Proceedings of Ajinomoto Animal Nutrition Technical Seminar. Amino Acid Nutrition in Broiler Diets. Pages 24-56. Bangkok, Thailand.

Tillman, P.B. and W.A. Dozier III., 2013. Current Amino Acid Considerations for Broilers : Requirements, Ratios and Economics. In Pre-Symposium from Proceedings of Arkansas Nutrition Conference by Adisseo, Rogers, AR. September 3-5.

Tillman, P.B., L. Mejia, A. Corzo and R.L. Shirley. 2011. Assessment of the digestible Arginine : lysine ratio of 28 to 42 day of age male broilers under an increasing temperature regimen. International Poultry Scientific Forum, Atlanta, GA, January. Nutrition Abstract and Oral presentation 99 : Page 29.

Tillman, P., K. Perryman, W. Dozier III. 2013. Increased dietary amino acid density from 1 to 35 d of age optimizes profitability in Hubbard M88 X Cobb 500 male broilers. International Poultry Scientific Forum, Atlanta, GA, January. Metabolism & Nutrition II Abstract and Oral presentation M61.

Tillman, P.B. and N. Sriperm. 2011b. Estimating Amino Acid Requirements of Broilers using Static : Production and Dynamic : Market Based Analysis. September 6. Pre-Symposium of Arkansas Nutrition Conference by Huvepharma, Rogers, AR.

Wecke, C and F. Liebert. 2013. Improving the Reliability of Optimal In-Feed Amino Acid Ratios Based on Individual Amino Acid Efficiency Data from N Balance Studies in Growing Chickens. Animals 3, 558-573.

Zhai, W., E.B. Peebles, C.D. Zumwalt, L. Mejia and A. Corzo. 2013. Effects of dietary amino acid density regimens on growth performance and meat yield of Cobb x Cobb 700 broilers. Journal of Applied Poultry Research 22:447-460.

Ziggers, D. 2011. Optimising nutrient density in a volatile market. All About Feed. Vol. 2., No. 3. 18-20.