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01996 Applied Poultry Science, I n c L-THREONINE FOR POULTRY: A REVIEW M.T. KlDD' and B. J. KERR Nutri-Quest, Inc, 14OOElbridge Payne Road Chesterjleld,MO 63017 Phone: (314) 537-4057 : ' F (314) 532-1710 ~ Primary Audience: Nutritionists, Researchers, Production Managers INTRODUCTION The extent to which dietary crude protein can be reduced without compromising bird performance remains problematic. Nevertheless, the inclusion of synthetic methionine and crystalline L-lysine has resulted in commercial diets being formulated for crude protein levels well below NRC recommendations [l]. The availability of L-threonine as a feed additive may allow poultry nutritionists, specifically turkey nutritionists, to further decrease dietary crude protein. Reducing dietary crude protein will: 1)improve nitrogen efficiency utilization; 2) reduce nitrogen excretion; 3) improve poultry tolerance of high ambient temperatures; and 4) reduce the level of ammonia in litter. However, as dietary crude protein decreases, the amino acid com1 To whom correspondence should be addressed position of the diet should match the bird's amino acid requirements for maintenance and tissue accretion in order to obtain optimum performance. W.C. Rose discovered threonine in 1935. Shortly after this discovery, threonine was deemed an essential amino acid for chicks [2, 31. Grau [4] evaluated DL-threonine and L-threonine in amino acid diets for chicks. Minimal biological activity was found in the former, and the requirement of the latter was 0.45% of diet. Since these and other early investigations of threonine in poultry, the 1980's and 90's have given rise to numerous threonine studies evaluating threonine requirements, threonine's efficacy in low protein diets, and enzymatic pathways responsible for threonine catabolism. Threonine is the third limiting amino acid in low crude protein Review Article 359 KIDD and KERR Because threonine, unlike most amino acids, is not transaminated, animals do not utilize its D-isomer and a-keto acid. DL-threonine has both a a n d /3 carbons, which are asymmetric and can yield four isomers: L (2S, X), D (2R, 3R), L-all0 (2S, 3R), and D-allo (2R, 3s). Baker [5, 61 suggested that DL-threonine should provide no more than 25% biological activity, which is based upon one-fourth of the molecule being L-threonine. Thus, poultry can utilize only L-threonine. Catabolism of L-threonine results largely in glucogenic products because it yields both pyruvate and propionate (Figure 1). Threonine dehydratase (E.C. 4.2.1.16), threonine dehydrogenase (E.C. 1.1.1.103), and threonine aldolase (E.C. 4.1.2.5) participate in threonine catabolism in chicks. However, threonine dehydrogenase accounts for most of the threonine oxidation in mammals in the fed state [7, 81. Threonine dehydratase (also known as serine dehydratase) uses pyridoxal-5'-phosphate to degrade threonine to a-ketobutyrate and ammonia, and diets for poultry. As techniques in fermentation of threonine-producing microorganisms improve, the commercial availability of L-threonine should increase. This review seeks to evaluate our current knowledge of L-threonine and provide insight on its future commercial application in the poultry industry. THREONINE METABOLISM Amino acid metabolism involves: 1) protein synthesis and degradation, 2) incorporation of amino acid nitrogen into uric acid, 3) conversion of amino acid carbon skeletons into glucose, fat, energy, or C02 and H20, and 4) formation of non-protein derivatives. Threonine participates in protein synthesis, and its catabolism generates many products important in metabolism (i.e., glycine, acetylCoA, and pyruvate). Poultry are not capable of synthesizing threonine de novo which makes it a nutritionally essential amino acid. Threonine (2-amino-3-hydroxybutyric acid, QH9N03) has a molecular weight of 119.12 and contains 11.76% nitrogen. Reutilization for degradation new protein synthesis Dietary protein or crystalline L-Thr Transamination Specialized products Glumgenic Catabolism of L-Threonine HO H I I Thr aldolase Thr dehydrogenase Acetaldehyde + Glycine t Acetyl-CoA t Serine 2 - amino -3- oxybutyrate J hinoacetone \r alpha-Ketobutyrate + NH; + Acetyl-coA + Glycine $. Pyruvate Pyruvate Serine $. Pyruvate -1GURE 1. Schematic representation of threonine catabolism Thr dehydratase 1 propionyl-&A 360 this reaction becomes important only during fasting. Threonine is degraded to glycine and acetaldehyde by threonine aldolase (also known as serine hydroxymethyl transferase) by a pyridoxal-5’-phosphate-catalyzed Schiff base cleavage. The nicotinamide adenine dinucleotide catalyzed reaction involving threonine dehydrogenase converts L-threonine to 2-amino-3oxybutyrate. Carbon skeletons from the catabolism of L-threonine generate pyruvate for energy or glucose production and glycine for metabolic needs (e.g., synthesis of protein, creatine, serine, uric acid, bile salts, and glutathione). Chicks require glycine or serine [9, 101. Baker et ai. [ll]evaluated the sparing effect of threonine on glycine by feeding chicks a completely purified glycine-free diet. These authors demonstrated that excess supplemental levels of dietary threonine (1.3%) heightened growth in chicks fed a glycine- and serine-free diet. When glycine was added to the high threonine diet, chick growth was decreased but gain:feed was improved. Thus, the glycine requirement of chicks can be partially spared by additional threonine; the reverse pathway (glycine to threonine), however, does not occur in chicks. Conversely, D’Mello [12] found that threonine does not spare glycine in the chick. Threonine’s ability to spare glycine in chicks remains subject to conjecture. Davis and Austic [13] evaluated tissue distributions and activities of threoninedegrading enzymes in female single comb white Leghorn chicks. The highest activity of threonine dehydrogenase was in the pancreas, whereas activities of threonine dehydratase and aldolase were highest in liver and muscle. These authors found that threonine aldolase and threonine dehydrogenase had the highest activity of the threonine-degradingenzymes in chicks [8]. A deficiency in a particular amino acid induced by an excess of one or more dietary amino acids is known as amino acid imbalance, as Salmon [14] previously reviewed. This review examines the nutritional basis of amino acid imbalance and argues that so-called amino acid toxicities documented in many early investigations may have been imbalances. As a case in point, this review describes a threonine deficiency imbalance caused by a slight excess of methionine in an amino acid L-THREONINE diet in rats. As dietary methionine increased, the growth rate decreased. Additional dietary threonine alleviated the decrease in growth. Moreover, excessive methionine causes threonine oxidation by increasing threonine dehydratase [15,16]. Because amino acid imbalance in rats has been studied extensively, it serves as a basis for comparison for amino acid imbalances that may occur in poultry. Yoshida et al. [171 studied the metabolic basis for amino acid imbalance by tracing the 14C-labeledlimiting amino acids in rats consuming equal quantities of balanced or imbalanced diets. These authors concluded that amino acid imbalance results in a more efficient incorporation of the growth-limitingamino acid into tissues, which decreases plasma levels of this amino acid. Lack of this plasma amino acid triggers a protective response that decreases food intake. Thus, rats given a choice between a proteinfree diet that will not support life or an imbalanced diet that will support life will consume the protein-free diet [18]. In poultry, excess lysine antagonizes arginine and excess leucine antagonizes isoleucine and valine, resulting in depressed growth. Some amino acid imbalances in poultry depress food intake without altering nutrient utilization (as reviewed by D’Mello [ 191). This agrees with findings of Cieslak and Benevenga [20], who showed that the imbalance in rats decreases voluntary food intake with minimal changes in threonine utilization. Thus, requirement studies in poultry that express nutrient levels as a percentage of diet and not mg intake/bird/day should pay careful attention to amino acid levels. By evaluating threonine decomposition enzymes in rats, Yamashita et al. [21] concluded that lysine may influence threonine metabolism. Yamashita and Ashida [22] studied effects of excessive levels of lysine and threonine on amino acid metabolism in rats because: 1) a deficiency of these two amino acids increases liver lipid deposition, and 2) these amino acids are not transaminated. Growth was not significantly depressed by high lysine or threonine. Rats possess a homeostatic mechanism that holds body lysine levels constant while body threonine fluctuates depending upon the amount present in the diet. The lack of such a homeostatic mechanism regulating threonine Review Article KIDD and KERR may render its requirement more variable in rats. When lysine levels fall below the requirement for poultry, all absorbed lysine that is not used for maintenance or not oxidized goes to skeletal muscle accretion. Many industry nutritionists formulate high lysine levels, above that recommended by the NRC [l],to keep pace with improved meat-yielding genetics of the commercial broiler. Increases in dietary lysine are implemented without consideration of other amino acids, i.e, threonine. However, an imbalance is not thought to occur between lysine and threonine in poultry due to the level of threonine in a corn and soybean meal diet, which may range from 0.75 to 0.83%. Threonine-imbalanceddiets were created in chicks by supplementing their basal diets with branched chain amino acids (6 dl00 g of diet) or a mixture of indispensableamino acids (5.6 @lo0 g of diet) [a] Hepatic . threonine dehydrogenase activity increased when chicks were fed either of the threonine-imbalanced diets. These authors hypothesized that the increase in threonine dehydrogenase activity may be responsible for the rapid decrease in plasma threonine when chicks consume a threonine-imbalanced diet. Rats were also evaluated in this study and had similar results to chicks. THREONINE CONTENT OF FEEDSTUFFS Threonine is the third limiting amino acid in corn-soybean meal poultry rations [24]. At protein levels typically used, however, diets composed mainly of corn and soybean meal are not limiting in threonine. Threonine, like lysine, is limiting in most cereals. Wheat, wheat midds, sorghum (milo), barley, and meat and bone meals are low in threonine, and their use may cause threonine to be a pressure point in poultry rations. Crystalline L-threonine may allow flexibility in diet formulation to utilize alternate ingredients. For example, peanut meal is first limiting in methionine and second limiting in threonine, and very high in protein and arginine. Depending on the price and seasonal availabilityof peanut meal, dietary supplementation of synthetic methionine and L-threonine may allow the inclusion of peanut meal in rations for broilers and turkeys. 361 Many milo sources contain high concentrations of tannins, which decrease bird performance and threonine availability [ E ] .In these experiments Teeter et al. demonstrated that threonine was the first limiting nutrient in milo. In addition, high-tannin milo depressed body weight and feed efficiency; however, the addition of supplemental threonine to the high-tannin milo improved performance to levels above that produced by milo void of tannins. Digestible amino acid values are not compared within this review; however, feed formulation practices utilizing true ileal digestibility values have clear advantages. Benefits from formulating on a digestible amino acid basis include: 1)amino acids being provided closer to the birds’ true requirement; and 2) formulation practices that are more flexible and allow inclusion of more alternate ingredients. Moreover, formulating on a digestible amino acid basis and utilizing alternate ingredients and crystalline amino acids may become economically advantageous. THREONINE RESEARCH IN BROILERS The threonine requirement for young broilers has been studied extensively in the past decade. During this time, estimates of threonine requirements in young male and female broilers ranged from 0.68 to 0.79% and 0.58 to 0.75% of the diet, respectively. In addition to varying requirements, nutrient levels that induce threonine imbalances and crude protein levels that affect threonine requirements are poorly understood. Commercial diets composed of corn, soybean meal, bakery meal, and poultry meals contain sufficient amounts of threonine for broiler production. Dietary inclusions of milo, wheat, wheat midds, and meat meals in broiler rations may cause threonine to be a pressure point in linear programming. Nevertheless, wide variations in published threonine requirements of broilers render the use of crystalline L-threonine problematic because they leave the optimal threonine level for broiler performance subject to conjecture. Thomas et al. [26] conducted two experiments with male broilers from 7 to 21 days of age fed graded levels of threonine which were added to a peanut meal, soybean meal, and JAPR 362 corn-based diet supplemented with synthetic amino acids to meet current Maryland standards. In both experiments, eight levels of threonine and two levels of coccidiostats (salinomycin and stenoral) were employed. Regardless of coccidiostat, the optimum level of threonine for weight gain and feed effciency ranged from 0.73% to 0.7%. The second experiment employed a lower level of threonine in the basal diet (OS%), which was achieved by substituting peanut meal for soybean meal. The threonine requirement for feed efficiency as determined by a regression equation was 0.73%. Thus, the threonine requirement for body weight gain and feed efficiency was reported to be between 0.73 and 0.77% of the diet. Previous frndings by these authors [27l demonstrated that the threonine requirement for broilers aged 14 to 21 days was between 0.80 and 0.85% of diet. Thus, estimates of the threonine requirement for broilers vary considerably within the same laboratory. However, Thomas et ai. [28] further evaluated the threonine requirement for both male and female broilers from 7 to 21 days of age. Synthetic amino acids were added to a corxdpeanut meal basal diet (0.55% threonine) so that all amino acids except threonine were at a minimum of 104% of the Maryland standards. The threonine requirements for males and females were estimated at 0.72% and 0.67%, respectively. This estimated threonine requirement for males was similar to results previously published [26]. Uzu [29] fed European experimental diets varying in threonine to broilers from 1 to 42 days of age. The four experiments utilized a variety of basal diets (corn/soy vs. cor a/ s o yl p e anu t me a 1; wh e a t/s o y v s . wheat/soy/peanut meal). The threonine requirement for growth and feed efficiency averaged across all experiments was 0.730.75% (1 to 21 days of age) and 0.68% (21 to 42 days of age). In addition, the threonine requirement varied little with respect to whether wheat or corn was used in the basal diets. This study indicated that threonine is not a limiting amino acid in typical or low protein corn-soybean meal diets. Robbins [30] found the threonine requirement of 1Cday-old female Peterson crossbred broiler chicks to be 3.7% of dietary crude protein. In these experiments, broilers received diets ranging from 10.98 to 18.3% crude L-THREONINE protein, which were supplemented with graded levels of L-threonine. The threonine requirement was determined by estimating the inflection point of the best-fit line [31]. Analysis of the threonine requirement as a percentage of diet ranged from 0.58 to 0.78%. Hence, the threonine requirement of chicks fed the high protein diet (20% crude protein) was 29% higher than that of chicks fed the low protein diet (15% crude protein). However, when the threonine requirement was expressed as a percentage of crude protein it ranged only from 3.77 to 3.87%, indicatingthat the threonine requirement increases as dietary crude protein increases. Threonine requirements expressed as a percentage of dietary crude protein, however, did not vary with the dietary crude protein content of the diet. If threonine is expressed as a percentage of dietary crude protein and the estimation of 3.7% is correct, the NRC [l] value of 0.80% threonine in a 23% crude protein diet for broilers from 1 to 21 days of age is too low. However, a previous section of this review discussed threonine’s sparing effect on glycine. Glycine provides two carbons and one nitrogen in the uric acid molecule. Indeed, a higher threonine requirement in high crude protein diets may indicate excess nitrogen excretion. The threonine requirement up to 3 wk of age for male Vantress x Arbor Acre broilers was determined by feeding threoninedeficient (0.59%) milo-soybean meal diets [32]. Broilers were fed a 15% crude protein diet from intact protein sources and supplemented with crystalline amino acids to obtain a diet which provided a minimum of 110% of the suggested amino acid recommendations [33]. Broilers in these experiments received dietary treatments from 7 to 18 or 21 days of age. The threonine requirements for weight gain and feed efficiency were 0.68% and 0.79%, respectively. The threonine requirement for feed efficiency conforms to the NRC [l]requirement of 0.80% of diet from 1 to 21 days of age. The 21 to 42-day threonine requirements for body weight gain and feed efficiency were estimated to be 0.66 and 0.68% of the diet, respectively [34]. The basal diet of wheat, corn gluten meal, soybean meal, and meat and bone meal contained 0.64% threonine and 20% crude protein. Abdominal fat was evaluated in Review Article KIDD and KERR addition to performance and was not affected by dietary threonine. This experiment suggests that the NRC [l]21 to 42-day requirement of 0.74% of diet is too high. Rangel-Lugo et ai. [35] evaluated the threonine requirements for weight gain and feed efficiency up to 14 days of age in chicks fed wheat-peanut meal-based diets of 20 and 25% crude protein. This study utilized Peterson x Hubbard broilers reared in environmentally controlled Petersime battery brooders. The threonine requirements for maximal weight gain in the 20 and 25% crude protein diets were 0.67 and 0.77%, respectively. These results are similar to Robbins [30] in that as dietary crude protein increases the threonine requirement increases, presumably for excess nitrogen excretion. In the 25% crude protein diets, the threonine requirements for weight gain were 0.82 and 0.86%. The threonine requirement (as a percentage of crude protein) was 3.44 in the 25% crude protein diet. Thus chicks receiving the 25% crude protein diet had a higher threonine requirement than those receiving the 20% crude protein diet. In addition to these requirements, the threonine requirement in broilers aged 16 to 28 days receiving a cordpeanut meal diet containing 20% crude protein was determined to be 0.63% of diet for weight gain and 0.69% of diet for feed efficiency. The threonine requirement for feed efficiency is higher than that of weight gain, and the threonine requirement increases as crude protein increases. Holsheimer et ai. [36]used typical European diets to test the threonine requirement of Hybrid male and female broiler chicks up to 28 days of age. In two experiments they evaluated eight graded levels of threonine and two crude protein levels of either 16 and 20% or 16 and 22%. Their design employed floor pens (22 chickdpen) with six replicationdtreatment. In Experiment 1, female chicks were fed threonine-supplemented diets from 10 to 28 days of age and the threonine requirement was 0.63%. In Experiment 2, male and female chicks were fed a threoninesupplemented diet from 7 to 21 days of age and the threonine requirement was 0.73%. These studies were conducted to demonstrate a minimum value for the threonine requirement. More importantly, when chicks received a 16% crude protein diet supplemented 363 with 0.25% threonine (total dietary threonine, OM%), they grew as well as chicks receiving a 22% crude protein diet containing 0.85% threonine from corn and soybean meal. Furthermore, chicks fed the low protein threonine-supplemented diet had superior feed conversion compared to those fed the 22% crude protein cordsoybean meal diet. These authors stated that nutritionists who implement low protein diets must make extrapolations from these results as to how much threonine can be supplemented for maximal profit. Thomas et al. (371 evaluated the threonine requirement in Ross x Avian male and female broilers aged 35 to 47 days. Peanut meal was added to the basal diet, which contained 18.4% crude protein and 0.56% threonine. L-threonine was added in 0.02% increments up to 0.68%. They suggested that the threonine requirement for finishing broilers does not exceed 0.56%. This requirement is much lower than that recommended by the NRC [l] of 0.68% for the 42 to 56-day period. Kharlakian et al. [38] evaluated the threonine requirements for weight gain and feed conversion in male and female Avian x Avian broilers aged 5 to 7 wk. Threonine-deficient diets consisted of corn and peanut meal and were adequate in all amino acids except threonine. Threonine requirements were estimated using broken line methodology. The estimated threonine requirement for weight gain and feed conversion was 0.57% in males. In females, the estimated threonine requirement was 0.52%for weight gain and 0.55% for feed conversion. Although these estimated requirements are below NRC [l] suggested recommendations, performance of male and female broilers receiving the corn-peanut meal diets was below that of male and female broilers receiving the corn-soybean meal control diet (containing 0.70% threonine). Kidd et al. [39] conducted two studies evaluating threonine responses in low crude protein diets utilizing threonine limiting ingredients. Experiment 1 evaluated graded levels of threonine (92 to 112% of the NRC) in milo, soybean meal, wheat, and meat and bone meal based diets from 1to 56 days of age. A linear improvement in feed conversion was observed from 1 to 42 days of age. This suggests that threonine may become more important in older birds, possibly because of a higher main- 364 tenance requirement. A second experiment was conducted in broilers aged 21 to 42 days, evaluating additional threonine in a low crude protein diet with adequate methionine and lysine or a low crude protein diet balanced with all essential amino acids except threonine. Weight gain was optimized in low crude protein diets containing 0.78% threonine, but was statistically the same as in low crude protein diets containing 0.66% threonine and the high crude protein diet containing0.78% threonine. However, the low crude protein diet with adequate essential amino acids and a threonine content of 0.78% had the lowest weight gain. Feed conversion was optimized in low crude protein diets containing 0.78% dietary threonine. In addition, efficiency of protein utilization for daily body weight gain was lowest in the high crude protein diet, but abdominal fat was lowest in the high crude protein diet. This study indicates that dietary crude protein in broilers 21 to 42 days old may be reduced from 20.0% to 16.8% provided that synthetic methionine, L-lysine, and L-threonine are added to the 16.8% crude protein diet. Studies have shown that low protein diets result in optimal feed conversions in broilers [36,40,41, 42, 43, 441. Other research, however, has demonstrated that low crude protein diets do not result in optimal feed conversions [45,46,47,48]. It is well known that low crude protein diets improve protein utilization by minimizing excesses of essential amino acids [48,49]. If reducing the crude protein content of the diet is favored, threonine’s importance may depend on the extent to which crude protein is reduced. Nakajima et al. [42] demonstrated that for broilers 21 to 65 days of age the addition of L-threonine, but not L-tryptophan, to a 16% crude protein diet adequate in total sulfur amino acids and lysine improves feed conversion to the level occurring with a 19% crude protein diet. Chicks’threonine requirement is variable. The ideal protein concept may minimize variability in threonine requirements, and all other essential amino acid requirements, by setting specific ratios of amino acids to lysine [50, 511. Exact amino acid requirements for many amino acids, especially in later growth of poultry, are not known. Thus, the ideal protein concept provides a basis for nutritionists to formulate diets to meet amino acid needs. Be- L-THREONINE cause the ideal protein concept has the potential to be an instrumental tool for linear programming for poultry nutritionists, specific ratios in the older bird for all amino acids should be validated experimentally. The threonine to lysine ratios are 67 and 70 from 1 to 21 and 21 to 42 days of age, respectively. These ratios of threonine to lysine should be evaluated in the older bird to test the efficacy of the ideal protein concept in comparison to typical levels of lysine and threonine currently fed in the industry. This is especiallyimportant when higher lysine is used to optimize white meat yields. Limitations in interpretation of research results to date primarily involve variations in crude protein levels, energy levels, digestible threonine levels in the basal diets, essential and nonessential amino acid levels, chick age, duration of study, and environmental conditions. Estimates of the threonine requirement for broilers aged 1 to 21 days have ranged between 0.60 and 0.84% of the diet. The range of crude protein levels used for past research in chicks (below 20% and above 23%) limits the practical extrapolation of threonine requirement studies because industry nutritionists currently formulate diets for chicks of this age to contain between 20 and 23% crude protein. Much controversy exists concerning the actual threonine requirement of broilers. Furthermore, the appropriate way to express threonine in requirement studies is subject to controversy (ix., as a percentage of diet, metabolizable energy, crude protein, or lysine). Notwithstanding that responses to threonine in body weight gains and feed conversions have been studied extensively in young broilers, requirement studies, particularly in older broilers, need to be conducted to establish specific threonine requirements for maintenance, performance, and carcass yields. THREONINE RESEARCH IN TURKEYS Research evaluating the threonine requirement in turkeys has been conducted only for poults up to 3 wk of age. Dunkelgod et al. [52] determined the threonine requirement to be 1.10% of diet for growth from 1to 2 wk in large white males. D’Mello [53]found that the Review Article KIDD and KERR threonine requirement for growth in the large white male was 0.94% from 1to 3 wk of age. Threonine requirements for growth from 4 to 18 wk of age in the 1994 edition of the NRC are based on computer models, not experimental research. Growing turkeys require 28 and 26% dietary protein from 0 to 4 and 4 to 8 wk of age, respectively [l].The benefits of reducing dietary protein for turkeys and supplementing rations with amino acids are well recognized. These benefits include increasing the efficiency of utilization of dietary protein, reducing nitrogen excretion, reducing intestinal disorders, improving litter quality, minimizing amino acid excesses, and maximizing profitability depending on the current price of oilseeds vs. crystalline amino acids. Moreover, research has shown that increasing dietary protein also increases amino acid requirements [M, 35, 541. The following section will discuss the availability of threonine in typical corn and soybean meal diets and the efficacy of threonine in low protein diets. Threonine is limiting in corn-soybean meal diets for young turkeys [55,56]. Stas and Potter [55] conducted experimentsin poults to determine which amino acids are limiting in a 22% crude protein diet consisting of corn and soybean meal and supplemented with 0.3% DL-methionine. The experimental design consisted of three diets fed from 8 to 18 or 19 days of age containing 1) 30% crude protein, 2) 22% crude protein, and 3) 22% crude protein plus all essential amino acids. Reductions in body weight gain by 9.3, 8.0, 6.0, and 4.1% were obtained when valine, lysine, threonine, or isoleucine was removed from the 22% crude protein diet supplemented with amino acids. This study suggested that the diets tested may have been more deficient in non-essential nitrogen than in any of the essential amino acids. Jackson et al. [56] conducted experiments similar to those of Stas and Potter [55] to determine relative deficiencies of lysine, threonine, valine, and nitrogen per se in low protein diets consisting of corn and soybean meal. These experiments demonstrated that 365 nitrogen per se, from the addition of 4% glutamic acid, is not a limiting factor for poult growth in a 22% crude protein diet consisting of corn-soybean meal. Furthermore, sulfur amino acids were more deficient than lysine, threonine, or valine in a corn-soybean meal diet containing 22% protein and 0.3% added DL-methionine. Dehulled soybean meal diets varying in protein and adequate in methionine were fed to poults to determine amino acid deficiencies in soybean meal [57]. Poults received a 30% crude protein diet and a 22% crude protein diet supplemented with essential amino acids. To determine what amino acids were limiting in a 22% crude protein diet, individual amino acids were deleted from the diet. Poults fed the amino acid-fortified 22% crude protein diet had body weight gains statistically equal to those of poults fed the 30% crude protein diet (288 vs. 300 g, respectively). Reductions in body weight gain by 19,16,11,7, and 6% were observed when valine, threonine, lysine, phenylalanine (or tyrosine or glycine), and isoleucine were removed from the 22% protein diet, respectively. This indicates that soybean meal as the sole protein source for turkeys, is more deficient in threonine than lysine. Recent broiler research [24] similarly shows methionine and threonine to be first and second limiting in soybean meal protein, with lysine and valine being equally third limiting. Decreasing dietary crude protein to approximately 90% of NRC suggested recornmendations and supplementing these diets with some essential amino acids can yield performance equal to that of diets adequate in protein [58,59,60,61].Most recently, Sell et al. [61] demonstrated that diets containing 93% of the NRC recommendation for crude protein with supplemental essential amino acids to 100% of NRC recommendations are adequate for production of commercial turkeys. Nevertheless, the extent to which dietary protein can be reduced remains problematic. Threonine, however, may be a key factor in allowing crude protein to fall below 90% of NRC recommendations while maintaining bird performance to market. JAPR L-THREONINE 366 CONCLUSIONS AND APPLICATIONS 1. Threonine is typically the third limiting amino acid in corn and soybean meal diets for both broilers and turkeys. 2. In practice, threonine may become a pressure point in linear programming with implementationof high dietary levels of threonine-limiting ingredients, particularly wheat, milo, barley, and meat and bone meals. 3. Dietary supplementation of L-threonine, along with synthetic methionine and L-lysine, may allow nutritionists to further reduce the inclusion of protein rich feedstuffs while maintaining bud performance. REFERENCES AND NOTES 1. Nalional Research CouncU, 1994. Nutrient Reuirements of Poult . 9th Rev. Edition. Natl. Acad. %res,Washington, D Z 2. Hegs(cd, D.M., 1944. Growth in chicks fed amino acids. J. Biol. Chem. 156247-251. 3. Almquist, HJ.andC.R Grau, 1944.The amino acid requirements of the chick. J. Nutr. 28:325-331. 4. Grau, C.R, 1949.The threonine requirement of the chick. J. Nutr. 37105-114. 5. Baker, D.H., 1986. Utilization of isomers and analo of amino acids and other sulfur compounds. Pages 137-178in: Progress in Food and Nutrition Science. RK. Chandra, ed. Pergamon Press, Elmsford, NY. 6. Baker, D.H., 1994. Utilization of precursors for Lamino acids. Pages 37-63 in: Amino Acids in Farm Animal Nutrition. J.P.F. D’Mello, ed. CAB Intl., Wallingford, U K 7. Ballem, O., A Cadenhead, AG. Calder, W.D. Rees, G.E bbley, M.F. Fuller, and P.J. Garlick, 1990. Quantitative partition of threonine oxidation in pigs: Effect of dietary threonine. Am J. Physiol. 259:EA83-E491. 8. Davk, AJ. and RE Auslic, 1 W a . Dietary threonine imbalance alters threonine dehydrogenase activity in isolated hepatic mitochondria of chicksand rats. J. Nutr. iwi~7-16n. 9. Akrabawi, S.S. and F.H. Kratzer, 1968. Effects of arginine or serine on the requirement for glycine by the chick. J. Nutr. 95:4148. 10. Baker, D.N., M. Sugahara, and H.M. Scolt, 1968. The glycine-serine interrelationship in chick nutrition. Poultry Sci. 4713761337. 11. Baker, D.H., T.M. Hill, and AJ. Klelss, 1972. Nutritional evidence concerning formation of lycine from threonine in the chick. J. Anim. Sci. 34:582-!86. 12. D’Mcllo. J.P.F.. 1973. As~ectsof threonine and domestlrus . >. Ey&e metabol&n in the c h i d utr. Metab. 15:357-363. 13. Davls, AT. and RE Austic, 1982. Threoninedegrading enzymes in the chicken. Poultry Sci. 61:21072111. 14. Salmon, W.D., 1958. The significance of amino acid imbalance in nutrition. Am. J. Clin. Nutr. 6437494. (m 15. Chrd-Clobq A, P. Robin, and M. Foreslier, 1972. Long-term adaptation of weanin rats to high dietary levels of methionine and serine. Nutr. 102209218. f. 16. Kat+ RS. and D.H. Baker, 1975. Methionine toxicity in the chick Nutritional and metabolic implications. I. Nutr. 105:1168-1175. 17. Yoshida, A, P.M.B. h u n g , Q.R Rogers, and A E Harper, 1966. Effect of amino acid imbalance on the fate of the limiting amino acid. J. Nutr. 89:8&90. 18.Sanahuja, J.C. and AIL Harper, 1963. Amino acid balance and imbalance. X. Effect of dietary amino acid pattern on plasma amino acid pattern and food intake. Am. I.Physiol. 204:68&691. 19. D’Mello, J.P.F., 1994. Amino acid imbalances, antagonisms, and toxicities. Pa es 63-97 in: Amino Acids in Farm Animal Nutrition. CA% Intl., Wallingford, U K 20. Cieslak, D.G. and NJ. Benevenga, 1984. The effect of amino acid excess on utilization by the rat of the limiting amino acid-threonine. J. Nutr. 11431871-1877. 21. Yamashifa, M., M. Fujimaki, and Y. Sakurai, 1967. Nutrition of threonine. Part 1V.Changes in activities of threonine decomposition enzymes in rat liver by excess feeding of lysine and threonine. Agr. Biol. Chem. 31:1047-1053. 22. Yamashita, K. and K. Ashida, 1971. Effect of levels of lysine and threonine on the metabolism of these amino acids in rats. I. Nutr. 101:1607-1614. 23. Davis, AJ. and R E Austic, 1994b. Dietary amino acid imbalance and metabolism of the limitin amino acid. Pages 70-31 in: Proc. Cornell Nutr. Conf.,\ochester, NY. 24. Fernandez, S.R, S. Aoyagi, Y. Han, C.M. Parsons, and D.H. Baker, 1994. Limiting order of amino acids in corn and soybean meal for growth of the chick. PoultIy Sci. 731887-1896. 25. Teeter, R.G., S. Sarani, M.O. Smlth, and C.A Hibberd, 1986. Detoxification of high tannin sorghum grains. Poultry Sci. 6567-71. 26. Thomas, O.P., AI. Zuckerman, M. Farran, and C.B. Tamplin, 1986. U ated amino acid re uirements of broilers. Pages 794%: Proc. Malyland dutr. Conf., Baltimore, MD. 27. Thomas, O.P., P.V. Twining, Jr., EH. Bossard, J . L Nicholson, and M. Rubin, 1979. Broiler chickstudies with threonine and lysine. Pages4448 in: Proc. Malyland Nutr. Conf., Baltimore, MD. 28.Thomas, O.P., M. Farran, C.B. Tamplin, and AI. Zuckerman, 1987. Broiler starter studies. I. The threonine requirements of male and female broiler chicks. 11. The body composition of males fed varying levels of Review Article KIDD and KERR protein and energy. Pages 3842 in: Proc. Maryland Nutr. Conf., Baltimore, MD. 29. Uzu, C.,1986. Threonine Requirement for Broilers. A E C Information Poultry 252, 03600 Commentry, France. 30. Robbins, K R , 1987.Threonine re uirement of the broiler chick as affected by protein lev3 and source. Poultry Sci. 66:1531-1534. 31.Robbins, K R , 1986.A method,SASprogram, and example for fitting the broken-line to growth data. Univ. Tenn. Exp. Sta. Res. Rep. No. 86-09. 32.Smlth, N.K., Jr. and P.W. Waldroup, 1988. Investieations of threonine reauirements of broiler chicks fed d h based on grain sorghum and soybean meal. Poultry S i . 67AO8-112. 33. National Research Councll, 1984. Nutrient Reuircments of Poult . 8th Rev. Edition. Natl. Acad. 8ress, Washington, D Z 34. P e w AM., Jr., C.L Colnago, and LS. Jensen, 1991. Threonine requirement of broiler chickens from 3 to 6 wk of age. Poultry Sci. 7O(Suppl):93. 35. Rangel-Lugo, M., C.-L Su,and RE Auslic, 1994. Threonine requirement and threonine imbalance in broiler chickens. Poultry Sci. 73670481. 36. Holsheimer, J.P., P.F.G. VereUken, and J.B. Schulie, 1994. Response of broiler chicks to threoninesupplementeddietsto4wkofage.Br. PoultrySci.35:551562. 37. Thomas, O.P., T.A Shellem, M. Sprague, and H.C. Kharlakian, 1995.Aminoacid requirementsduring the withdrawal period. Pa es 71-75 in: Proc. Maryland Nutr. Conf., Baltimore, M%. 38. Kharlakian, H.K., T.A Shellem, O.P. Thomas, and C.K. Baer, 1996.Lysine, methionine, and threonine requirements in broilers durin the withdrawal period. Pa es 53-63 in: Proc. Marylancf Nutr. Conf., Baltimore, M%. 39. Kidd, M.T., BJ. Kerr, J.D. Flrman, and S.D. Boling, 1996.Growth and carcass characteristics of broilers fed low-protein, threonine-supplemented diets. J. Appl. Poultry Res. 5:173-179. 40.Lipstein, B. and S. Bornstein, 1975.The replacement of some of the saybean meal b the first limiting amino acids in practical broiler diets. ZSpecial additions of methionine and lysine as partial substitutes for protein in finisher diets. Br. Poultry Sci. 16189-200. 41. Uzu, G., 1982. Limit of reduction of the protein level in broiler feeds. Poultry Sci. 61:1557-1558. 42. Nakajima, T., H. Kishl, T. Kusubae, H. Wakamalsu, and Y. Kusulani, 1985. Effect of L-threonine and DL-tryptophan supplementation to the lowproteinpractical broiler finisher diet. Jpn. Poultry Sci. 2210-16. 43.Summers, J.D. and S. Leeson, 1985.Broiler carcass composition as affected by amino acid supplementation. Can. J. Anim. Sci. 65717-723. 44. Stilbom, H.L, 1990. Lysine and methionine reuirements of broilers 3 to 6 wk of a e. Ph.D. Thesis. bniversity of Arkansas, Fayetteville, A k 45. Twining, P.V., Jr., O.P. Thomas, and E.H. Bossard, 1976. The number of feathers on the litter: 367 Another criterion for evaluating the adequacy of broiler diets. Poultry Sci. 55:1u)o-1207. 46. Twining, P.V., Jr., O.P. Thomas, and E.H. of birds on the Bosard, 1978. Effect of diet and carcass composition of broilers at 8 9 ,and 59 days of age. Poultry Sci. 57:492497. 47.Humitz, S., I. Plavnlk, I. Bartov, and S. Bornstein, 1980.The amino acid requirements of chicks: Ekperimental validation of model-calculated requirements. Poultry Sci. 59247G2479. 48.Fancher, B.I. and LS Jensen, 1989.Influence on performance of three- to six-week-old broilers of varying dietary protein contents with supplementation of essential amino acid requirements. Poultry Sci. 68:113-123. 49. Waldroup, P.W., RJ. Mitchell, J.R Payne, and K.R Haun, 1976.Performance of chicks fed diets formulated to minimize excess levels of essential amino acids. Poultry Sci. 55:243-253. 50. Baker, D.H., 1994. Ideal amino acid profile for maximal protein accretion and minimal nitrogen excretion in m n e a n d poultry. Pages 134-139 in: Proc. Cornell Nutr. Conf., Rochester, NY. 51.Baker, D.H., 1995.Ideal rotein for broiler chicks. Pages 1-13 in: Proc. Multistate Foultry Nutr.and Feeding Conf., Indianapolis, IN. 52. Dunkelgod, K.E, P.E Waibel, R.J. Sirny, and D.C. Snebinger, 1970.An improved free amino acid diet for the growing turkey. Poultry Sci. 49261-268. 53. D’Mello, J.P.F., 1976.Requirements of the young turkey for sulfur amino acids and threonine: Comparison with other species. Br. Poultry Sci. 17157-162. 54. Abebe, S and T.R Morris, 1990. Note on the effects of protein concentration on responses to dietary lysine bychicks. Br. Poultry Sci. 31255-260. 55. Stas, RJ. and LM. Potter, 1982.Deficient amino acids in a 22% protein corn-s ean meal diet for young turkeys. Poultry Sci. 61:933-9g 56. Jackson, S, RJ. Stas, and LM. Potter, 1983. Relative deficiencies of amino acids and nitrogen ms in low protein diets for young turkeys. Poultry Sci. 62:1117-1119. 57.Blair, M.E and LM. Poller, 1987.Deficient amino acids in protein of dehulled so ean meal for young turkeys. Poultry Sci. 66:1813-181? 58. Spencer, C.K., 1984. Minimum rotein requirements of turkeys fed adequate levels oflysine and methionine. Masters Thesis, University of Arkansas, Fayetteville, A R 59.Sell, J.L, P.R Ferket, C.R.Angel, S.E Scheideler, F. Escribano, and I. Zatarl, 1989. Performance and carcass characteristics of turkey toms as influenced by dieta protein and metabolizable energy. Nutr.Rep. Intl. 4097&292. 60.Sell, J.L, 1993.Influence of metabolizable energy feedingsequence and dietaryprotein on performance and selected carcass traitsof tom turkeys. Poultry Sci. 72521534. 61.Sell, J.L, M.J. JelTrey, and B.J. Kerr, 1994.Influence of amino acid supplementation of low-protein diets and metabolizable energy feeding sequence on performance and carcass composition of toms. Poultry Sci. 73:1867-1880.