Digestible lysine and threonine requirements of male turkeys from days 8 to 21 and days 29 to 42

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1 2012 Poultry Science Association, Inc. Digestible lysine and threonine requirements of male turkeys from days 8 to 21 and days 29 to 42 L. B. Linares,* R. A. Murarolli,* E. A. Guaiume, R. B. Shirley, D. Hoehler, D. R. Ledoux,* 1 and J. D. Firman * * Department of Animal Sciences, University of Missouri, Columbia 65211; Cargill Turkey Production LLC, Wichita, KS 67202; Ajinomoto Heartland Inc., Chicago, IL 60631; and Evonik Degussa Corporation, Kennesaw, GA Primary Audience: Nutritionists, Feed Millers SUMMARY Two experiments were conducted to determine the digestible lysine (dlys) and digestible threonine (dthr) requirements of Nicholas White male turkeys from d 8 to 21 (experiment 1) and d 29 to 42 (experiment 2). In experiment 1, the reduced-cp (25% CP) basal diet supplied 1.14% dlys and 0.56% dthr. To determine the requirement for dthr, the level of dlys was kept at 1.50%, and the 7 dietary dthr treatment levels ranged from 0.56 to 1.04%, in 0.08% increments. For the dlys requirement, the level of dthr was kept at 1.04%, and the 7 dietary dlys treatment levels ranged from 1.14 to 1.50%, in 0.06% increments. When BW gain and feed conversion were used as response variables and the results of the break-point analyses were considered, the dlys requirements were estimated to be 1.36 and 1.39%, respectively, and the dthr requirements were estimated to be 0.74 and 0.81%, respectively, in experiment 1 (d 8 to 21). In experiment 2 (d 29 to 42), the reduced-cp (24% CP) basal diet supplied 1.06% dlys and 0.50% dthr. To determine the requirement for dthr, the level of dlys was kept at 1.42%, and the 7 dietary dthr treatment levels ranged from 0.51 to 0.99%, in 0.08% increments. For the dlys requirement, the level of dthr was kept at 0.99%, and the 7 dietary dlys treatment levels ranged from 1.06 to 1.42%, in 0.06% increments. When BW gain and feed conversion were used as response variables and the results of the break-point analyses were considered, the dlys requirements were estimated to be 1.27 and 1.29%, respectively, and the dthr requirements were estimated to be 0.72 and 0.76%, respectively, in experiment 2 (d 29 to 42). Key words: digestible lysine, digestible threonine requirement, male turkey 2012 J. Appl. Poult. Res. 21 : DESCRIPTION OF PROBLEM There is increasing demand for poultry meat worldwide, mainly because of its lower cost when compared with other meats such as beef and pork, and also because it is an excellent source of protein with a low concentration of fat, which is especially true for turkey meat. The overall consumption of turkey meat in the world is about 4.7 million metric tons annually, and the United States is responsible for almost 50% of all consumption [1]. The United States is 1 Corresponding author: ledouxd@missouri.edu

2 Linares et al.: DIGESTIBLE AMINO ACIDS AND MALE TURKEYS 385 Table 1. Coefficients of apparent ileal amino acid (AA) digestibility for ingredients used in the experimental diets and minimum formulated ideal protein ratios of AA to digestible lysine Digestibility coefficient, 1 % AA Corn SBM PNM MBM AA:lysine, % Lysine Threonine Methionine Cysteine Methionine + cysteine Arginine Isoleucine Leucine Histidine Valine Tryptophan Phenylalanine SBM = soybean meal; PNM = peanut meal; MBM = meat and bone meal. the number one producer of turkey meat as well, with 2.5 million metric tons produced annually, which is about 50% of worldwide production. To stimulate the production and consumption of turkey meat, it is necessary to decrease the cost of the diets without impairing the growth performance of the birds. The use of the ideal protein (IP) concept to formulate diets for turkeys using digestible amino acid (AA) values is one tool that can be used to reduce the cost of the diets, with the additional benefit of a potential reduction in excreta nitrogen when compared with turkeys fed diets formulated on a CP basis or on a total AA basis. Current NRC [2] AA requirement recommendations for turkeys are based on research done using total AA. Agri Stats [3] nutrient recommendations for turkeys are also based on CP and total AA. Few reports exist in the literature on the digestible AA requirements of turkeys. To date, digestible lysine (dlys) and sulfur AA requirements have been determined for starting turkeys [4 11]. Only 1 trial has been conducted to determine the requirements for digestible threonine (dthr) for starter poults [12]. The NRC [2] recommendations of total lysine (tlys) and total threonine (tthr) for turkeys are 1.60 and 1.00%, respectively, from 0 to 4 wk of age and 1.50 and 0.95%, respectively, from 4 to 8 wk of age. To date, no data are available in the literature on dthr requirements for turkeys raised to market weight. The objective of this research was to determine the dlys and dthr requirements of Nicholas White male turkeys from d 8 to 21 and from d 29 to 42. MATERIALS AND METHODS Experiment 1 Housing. A total of 1,400 eight-day-old Nicholas White male poults [13] were wing banded and weighed individually, and after the sorting procedure, 1,152 poults were distributed into the 14 treatments, in 96 pens, with 12 birds per pen. Birds were fed the experimental diets from d 8 to 21. From hatch to d 7, poults were fed a diet formulated to meet the requirements suggested by NRC [2]. The poults were housed and maintained using standard husbandry practices. Birds were housed in a curtain-sided building with the temperature controlled by circulating fans and a heater. Birds were maintained on a 24-h constant-light schedule and allowed access to feed and water ad libitum. All procedures were conducted in accordance with the University of Missouri Animal Care and Use Guidelines and approved protocols. Sorting Procedures for Experiments 1 and 2. The birds needed for the 2-wk experiment plus an additional 20% were weighed individually, and the lighter and heavier birds were not used. The birds were then randomized to the 96 pens according to their BW, using the Microsoft Excel randomization tool [14], to obtain average pen weights that were not different.

3 386 JAPR: Research Report Dietary Treatments. Values of apparent AA digestibility of the ingredients and minimum IP AA ratios to dlys of the formulated diets for both experiments are presented in Table 1. Ileal AA digestibility of ingredients was determined using 3-wk-old intact male turkey poults. Eighteen-day-old poults were fasted for 1 d and then fed the test ingredients plus chromium for 5 d. On d 25, the poults were euthanized and ileum samples were collected for determination of ileal AA digestibility. Experiment 1 included 7 titration levels of dlys and 7 titration levels of dthr, totaling 13 treatments (the summit treatment was common to both the dlys and dthr trials), plus an industry average positive control (PC). The reduced-cp (25% CP) corn, soybean meal (SBM), peanut meal, and meat and bone meal (MBM) basal diet (Table 2) supplied 1.14% dlys and 0.56% dthr. To determine the requirement for dthr, the level of dlys was kept at 1.50%, and the 7 dietary dthr treatment levels ranged from 0.56 to 1.04%, in 0.08% increments. For the dlys requirement, the level of dthr was kept at 1.04%, and the 7 dietary dlys treatment levels ranged from 1.14 to 1.50%, in 0.06% increments. The individual titration diets were prepared by addition of the AA being evaluated (lysine or threonine) to the negative control basal diet. The PC diet was an industry average diet containing 29% CP and 3,000 kcal/ kg of ME [3], based on corn, SBM, and MBM as presented in Table 2. Experiment 2 Housing. A total of 1,280 Nicholas male poults (29 d old) that were not used in the first experiment were weighed individually, and after the sorting procedure, 1,056 poults were distributed into the 14 treatments, in 96 pens, with 11 birds per pen. Birds were fed experimental diets from d 29 to 42. Dietary Treatments. There were 7 titration levels of dlys and 7 titration levels of dthr, totaling 13 treatments (the summit treatment was common to both the dlys and dthr trials), plus an industry average PC dietary treatment. The reduced-cp (24% CP) corn, SBM, peanut meal, and MBM meal basal diet supplied 1.06% dlys and 0.51% dthr (Table 3). To determine the requirement for dthr, the level of dlys was kept Table 2. Composition of the negative control basal and positive control diets fed to turkeys from 8 to 21 d of age (%) Item Negative control basal diet Positive control diet Ingredient Corn Soybean meal Peanut meal Meat and bone meal Dicalcium phosphate Limestone Salt Soybean oil l-lysine hydrochloride dl-methionine l-threonine Choline chloride Trace mineral premix Vitamin premix Selenium premix Copper sulfate Sodium bicarbonate Avatec 20% BMD l-histidine l-isoleucine l-tryptophan l-valine Calculated composition ME 3,000 3,000 CP Digestible lysine Digestible threonine Analyzed composition CP Total lysine Total threonine The trace mineral mix provided the following (mg/kg of diet): manganese, 110 (MnO 2 ); zinc, 110 (ZnSO 4 ); iron, 60 (FeSO 4 7H 2 O); iodine, 2.0 (ethylenediamine dihydroiodide). 2 The vitamin mix supplied the following (IU or mg/kg of feed): vitamin A (retinyl acetate), 13,200 IU; cholecalciferol, 5,775 IU; vitamin E (dl-α-tocopheryl acetate), 21 IU; niacin, 82.5 mg; calcium pantothenate, 25 mg; riboflavin, 10 mg; pyridoxine, 3.3 mg; menadione sodium bisulfite, 2.5 mg; folic acid, 2.1 mg; thiamine mononitrate, 1.7 mg; biotin, 0.33 mg; cyanocobalamin, 20 µg; and ethoxyquin, 83 mg. 3 The selenium premix provided 0.3 mg/kg of selenium (Na 2 SeO 3 ). 4 Avatec 20% provided 75 mg/kg of lasalocid sodium (Alpharma, Bridgewater, NJ). 5 BMD-50 provided 25 mg/kg of bacitracin methylene disalicylate (Alpharma, Fort Lee, NJ).

4 Linares et al.: DIGESTIBLE AMINO ACIDS AND MALE TURKEYS 387 Table 3. Composition of the negative control basal and positive control diets fed to turkeys from 29 to 42 d of age (%) Item Negative control basal diet Positive control diet Ingredient Corn Soybean meal Peanut meal Meat and bone meal Dicalcium phosphate Limestone Salt Soybean oil l-lysine hydrochloride dl-methionine l-threonine Choline chloride Trace mineral premix Vitamin premix Selenium premix Copper sulfate Sodium bicarbonate Avatec 20% BMD l-histidine l-isoleucine l-tryptophan l-valine Calculated composition ME 3,100 3,100 CP Digestible lysine Digestible threonine Analyzed composition CP Total lysine Total threonine The trace mineral mix provided the following (mg/kg of diet): manganese, 110 (MnO 2) ; zinc, 110 (ZnSO 4 ); iron, 60 (FeSO 4 7H 2 O); iodine, 2.0 (ethylenediamine dihydroiodide). 2 The vitamin mix supplied the following (IU or mg/kg feed): vitamin A (retinyl acetate), 13,200 IU; cholecalciferol, 5,775 IU; vitamin E (dl-α-tocopheryl acetate), 21 IU; niacin, 82.5 mg; calcium pantothenate, 25 mg; riboflavin, 10 mg; pyridoxine, 3.3 mg; menadione sodium bisulfite, 2.5 mg; folic acid, 2.1 mg; thiamine mononitrate, 1.7 mg; biotin, 0.33 mg; cyanocobalamin, 20 µg; and ethoxyquin, 83 mg. 3 The selenium premix provided 0.3 mg/kg of selenium (Na 2 SeO 3 ). 4 Avatec 20% provided 75 mg/kg of lasalocid sodium (Alpharma, Bridgewater, NJ). 5 BMD-50 provided 25 mg/kg of bacitracin methylene disalicylate (Alpharma, Fort Lee, NJ). at 1.42%, and the 7 dietary dthr levels ranged from 0.51 to 0.99%, in 0.08% increments. For the dlys requirement, the level of dthr was kept at 0.99%, and the 7 dietary dlys levels ranged from 1.06 to 1.42%, in 0.06% increments. The individual titration diets were prepared by addition of the AA being evaluated (lysine or threonine) to the negative control basal diet. The PC industry average diet had 27.5% CP and 3,100 kcal/kg of ME [3], based on corn, SBM, and MBM as presented in Table 3. Measurements for Experiments 1 and 2. Mortality was recorded as it occurred. All birds were inspected daily and health-related problems were recorded. Data were collected during the last 2 wk of each 3-wk period (for example, in experiment 1, data were collected during wk 2 and 3). The birds were weighed by pen at the end of the last week of the period. The initial BW was subtracted from the final BW to determine BW gain (BWG) of the birds in the 2-wk period. Total feed intake was determined by subtracting the feed left from the initial feed offered to the birds. Average feed intake was adjusted for mortality to more accurately reflect the ac- Table 4. Growth performance of male turkeys fed graded levels of digestible threonine (dthr) from 8 to 21 d of age 1,2 Item Feed intake, g BW gain, 3 g Feed:gain, 4 g/g dthr, 5 % b 247 d c a 277 c c a 286 b bc a 291 ab b a 293 ab b a 296 a b a 299 a b c 269 c a Pooled SEM a d Values within columns with no common superscript differ significantly (P < 0.05). 1 Data are means of 7 replicate pens of 12 poults per pen, except treatment 0.96% dthr, which had 6 replicate pens of 12 poults per pen. 2 Broken-line and quadratic responses (P < ). 3 Regression analysis using the 2-slope broken-line model [16, 17] indicated a requirement of 0.74% dthr, R 2 = Regression analysis using the 2-slope broken-line model [16, 17] indicated a requirement of 0.81% dthr, R 2 = The basal diet contained 1.14% digestible lysine (dlys) and 0.56% dthr. The positive control diet contained 1.55% dlys and 0.89% dthr.

5 388 JAPR: Research Report Figure 1. Broken-line and quadratic analyses of BW gain (BWG) of male turkeys fed graded levels of digestible threonine (dthr) from 8 to 21 d of age. The minimal dthr requirement for BWG using the broken-line analysis was 0.74% (y = x , R 2 = 0.91). The BWG data were also fitted to a quadratic regression equation (y = x x , R 2 = 0.93). The level of dthr that maximized BWG (i.e., upper asymptote) was calculated to be 0.95% of the diet, with 90% of this value being 0.85%. The first intercept x-value of the broken line (on the plateau) and the quadratic fitted line occurred at 0.84% dthr. Std diet = standard diet. cess of individual birds in a pen to feed during the testing period, using the following equation: AFI = (TFI/TBD) D, where AFI is average feed intake; TFI is total feed intake (kg), TBD is total bird days (d), D is the duration of the test period (d), and TBD is (number of living birds per pen at the conclusion of the trial D) + [number of days that dead bird(s) had access to feed]. The feed-to-gain ratio (F:G) was calculated by dividing the average feed intake by the BWG. Statistical Analyses. The experimental design used in the 2 studies was a completely randomized design with 14 treatments, and pen was designated as the experimental unit. Data were analyzed using the ANOVA procedure of SAS [15]. Treatment means were compared using Fisher s LSD option of SAS [15]. All statements of significance are based on a 0.05 level of probability. Pen means were used with the brokenline analysis procedure of SAS [15] to estimate the requirements for dlys and for dthr for each experiment, using BWG and F:G as dependent variables. The NRM.xls Microsoft Excel workbook was used as a tool to prepare charts fitting the segmented regression with linear segments of the broken-line model [y = (L + U) (R x) + V (x R), where (R x) is defined as zero at values of x > R, and (x R) is defined as zero when x < R] and the segmented regression with quadratic segments of the model [y = (L + U) (R x) 2, where L is the constant rate of the asymptote of the first segment, R is the abscissa of the inflection in the curve, U is the slope of

6 Linares et al.: DIGESTIBLE AMINO ACIDS AND MALE TURKEYS 389 the line for x < R, and V is the slope of the line at x > R] [16, 17], determining the dietary AA level required for maximal BWG and minimal F:G (x-value at the maximum y-value of the quadratic response curve). A value of 95% of the x-value required for maximal y was selected as a subjective estimate of the requirement. An objective estimate of digestible AA requirements from the quadratic models was determined by establishing the first point at which the quadratic response curve intersected the plateau value established from the one-slope fitted broken-line. The intercept x-value was then calculated using the quadratic regression equation once the y-plateau value of the broken-line was determined. Ratios of dthr to dlys were based on the higher requirement estimates for BWG and F:G for each selected method. RESULTS AND DISCUSSION Experiment 1 dthr. Feed intake, BWG, and F:G of turkeys from 8 to 21 d were affected by treatments (P < ; Table 4). A gradual increase in the AFI of turkeys was observed in response to an increase in dietary dthr from 0.56 to 0.64%. A gradual increase in BWG and a gradual decrease in F:G of turkeys were also observed in response to an increase in dietary dthr from 0.56 to 0.80%. Beyond that level, no significant change was observed in BWG or F:G. Body weight gain of birds fed the PC treatment did not differ significantly (P > 0.05) from treatments containing a minimum of 0.64% dthr. Feed intake and F:G of birds fed the PC treatment differed signifi- Figure 2. Broken-line and quadratic analyses of the feed-to-gain ratio (F:G) of male turkeys fed graded levels of digestible threonine (dthr) from 8 to 21 d of age. The minimal dthr requirement for F:G using the broken-line analysis was 0.81% (y = x , R 2 = 0.98). The F:G data were also fitted to a quadratic regression equation (y = x x , R 2 = 0.97). The level of dthr that maximized F:G (i.e., lower asymptote) was calculated to be 0.97% of the diet, with 90% of this value being 0.87%. The first intercept x-value of the broken line (on the plateau) and the quadratic fitted line occurred at 0.86% dthr. Std diet = standard diet.

7 390 JAPR: Research Report Figure 3. Broken-line and quadratic analyses of BW gain (BWG) of male turkeys fed graded levels of digestible lysine (dlys) from 8 to 21 d of age. The minimal dlys requirement for BWG using the broken-line analysis was 1.36% (y = x , R 2 = 0.96). The BWG data were also fitted to a quadratic regression equation (y = x x , R 2 = 0.98). The level of dlys that maximized BWG (i.e., upper asymptote) was calculated to be 1.46% of the diet, with 90% of this value being 1.31%. The first intercept x-value of the broken line (on the plateau) and the quadratic fitted line occurred at 1.42% dlys. Std diet = standard diet. cantly (P < 0.05) from those of all other treatments. Birds fed the standard diet performed below expectations in experiment 1 (Figures 1, 2, 3, 4) but met expectations in experiment 2 (Figures 5, 6, 7, 8). Broken-line and quadratic regression analyses of the data for BWG and F:G are presented in Figures 1 and 2, respectively. Based on the estimates of both models, the one-slope breakpoint, the first intercept x-value of the brokenline and the quadratic model, and 90% of the upper asymptote, the dthr requirements using BWG were 0.74, 0.84, and 0.91%, respectively, whereas using F:G, the dthr requirements were 0.81, 0.86, and 0.92%, respectively, for male turkeys from 8 to 21 d of age. dlys. Feed intake, BWG, and F:G of turkeys from 8 to 21 d were affected by treatments (P < ; Table 5). A gradual increase in feed intake of turkeys was observed in response to an increase in dietary dlys from 1.14 to 1.20%. A gradual increase in BWG and a gradual decrease in F:G of turkeys were also observed in response to an increase in dietary dlys from 1.14 to 1.26%. Beyond that level, no significant change was observed in BWG or F:G. The BWG of birds fed the PC treatment did not differ significantly (P > 0.05) from the treatments containing a minimum of 1.20% dlys. Feed intake and F:G of birds fed the PC treatment differed significantly (P < 0.05) from those of all other treatments. Broken-line and quadratic regression analyses of the data for BWG and F:G are presented in Figures 3 and 4, respectively. Based on the estimates of both models, the one-slope breakpoint, the first intercept x-value of the brokenline and the quadratic model, and 90% of the

8 Linares et al.: DIGESTIBLE AMINO ACIDS AND MALE TURKEYS 391 upper asymptote, the dlys requirements using BWG were 1.36, 1.42, and 1.39%, respectively, whereas using F:G, the dlys requirements were 1.39, 1.43, and 1.60%, respectively, for male turkeys from 8 to 21 d of age. For this period, the dthr-to-dlys ratios were 0.58, 0.60, and 0.58 for the one-slope break-point, the first intercept x-value of the broken-line and the quadratic model, and 90% of the upper asymptote methods, respectively. Experiment 2 dthr. Feed intake, BWG, and F:G of turkeys from 29 to 42 d were affected by treatments (P < ; Table 6). A gradual increase in feed intake of turkeys was observed in response to an increase in dietary threonine from 0.51 to 0.75%. A gradual increase in BWG of turkeys in response to an increase in dietary threonine was also observed from 0.51 to 0.91%, as well as a gradual improvement in F:G from 0.51 to 0.83%. Beyond these levels, no significant change was observed in AFI, BWG, or F:G. The BWG and F:G of birds fed the PC treatment did not differ significantly (P > 0.05) from treatments containing a minimum of 0.91 and 0.75% dthr, respectively. Broken-line and quadratic regression analyses of the data for BWG and F:G are presented in Figures 5 and 6, respectively. Based on the estimates of the 3 models, the one-slope breakpoint, the first intercept x-value of the brokenline and the quadratic model, and 95% of the upper asymptote, the dthr requirements using BWG were 0.72, 0.79, and 0.84%, respectively, whereas when using F:G, the dthr requirements were 0.76, 0.81, and 0.86%, respectively, for male turkeys from 29 to 42 d of age. Figure 4. Broken-line and quadratic analyses of the feed-to-gain ratio (F:G) of male turkeys fed graded levels of digestible lysine (dlys) from 8 to 21 d of age. The minimal dlys requirement for F:G using the broken-line analysis was 1.39% (y = x , R 2 = 0.93). The F:G data were also fitted to a quadratic regression equation (y = x x , R 2 = 0.92). The level of dlys that maximized F:G (i.e., low asymptote) was calculated to be 1.68% of the diet, with 90% of this value being 1.51%. The first intercept x-value of the broken line (on the plateau) and the quadratic fitted line occurred at 1.43% dlys. Std diet = standard diet.

9 392 JAPR: Research Report Figure 5. Broken-line and quadratic analyses of BW gain (BWG) of male turkeys fed graded levels of digestible threonine (dthr) from 29 to 42 d of age. The minimal dthr requirement for BWG using the broken-line analysis was 0.72% (y = x , R 2 = 0.99). The BWG data were also fitted to a quadratic regression equation (y = x x , R 2 = 0.99). The level of dthr that maximized BWG (i.e., upper asymptote) was calculated to be 0.88% of the diet, with 90% of this value being 0.79%. The first intercept x-value of the broken line (on the plateau) and the quadratic fitted line occurred at 0.79% dthr. Std diet = standard diet. dlys. Feed intake, BWG, and F:G of turkeys from 29 to 42 d were affected by treatments (P < ; Table 7). A gradual increase in feed intake of turkeys was observed in response to an increase in dietary dlys from 1.06 to 1.18%. A gradual increase in BWG of turkeys in response to an increase in dietary dlys was also observed from 1.06 to 1.30%, as well as a gradual improvement in F:G from 1.06 to 1.24%. Beyond those levels, no significant change was observed in AFI, BWG, or F:G. The BWG and F:G of birds fed the PC treatment did not differ significantly (P > 0.05) from treatments containing the minimum of 1.24 and 1.18% dlys, respectively. Broken-line and quadratic regression analyses of the data for BWG and F:G are presented in Figures 7 and 8, respectively. Based on the estimates of the 3 models, the one-slope breakpoint, the first intercept x-value of the brokenline and the quadratic model, and 90% of the upper asymptote, the dlys requirements using BWG were 1.27, 1.32, and 1.30%, respectively, whereas when using F:G, the dlys requirements were 1.29, 1.36, and 1.32%, respectively, for male turkeys from 29 to 42 d of age. For this period, the dthr-to-dlys ratios were 0.59, 0.59, and 0.66 for the one-slope break-point, the first intercept x-value of the broken-line and the quadratic model, and 95% of the upper asymptote methods, respectively. Based on the feed intake and BWG responses to dietary dthr and dlys in both experiments, the basal diet was deficient in both AA. Supplementation of dl-methionine, l-lysine hydrochloride, l-threonine, l-histidine, l-isoleucine, l-tryptophan, and l-valine was required so that the essential AA met the IP ratio compared with the summit dlys level. Supplementation of l- glutamic acid was necessary for the dietary treatments to reach the minimum CP level. The

10 Linares et al.: DIGESTIBLE AMINO ACIDS AND MALE TURKEYS 393 poor performance of birds fed the standard diet in experiment 1 was unexpected. The diet was analyzed for a variety of nutrients and found to be on target based on the formulation, so at this point the poor performance of birds fed the standard diet is an unexplained anomaly. In experiment 1, the dthr requirements for male turkeys from 8 to 21 d was estimated to be 0.74% when using BWG (Figure 1) and 0.81% when using F:G (Figure 2). These requirements are high when compared with the results for dthr reported by Kamyab and Firman [12], who found the dthr requirements to be 0.67 and 0.74% for BWG and F:G, respectively, for the same period. However, Kamyab and Firman [12] estimated the requirements for turkey hens, and the trial was conducted in battery cages, which diminishes the maintenance requirements of the poults [18]. Firman and Guaiume [11] found the dthr requirement to be between 0.83 and 0.86% for male poults for the first 3-wk period. Kidd et al. [19] determined the optimal dietary levels of tthr for British United Turkeys male turkeys for BWG and F:G for the hatch to 3-wk period to be 0.93 and 0.97%, respectively. Lehmann et al. [20] reported the optimal dietary level of tthr for male turkeys for growth and feed conversion for the hatch to 4-wk period to be 0.95%. When a digestibility coefficient of 82% for threonine was applied [unpublished results from our laboratory, 21 26], the results of Kidd et al. [19] and Lehmann et al. [20] agreed with the dthr requirements determined in the current study. With this conversion to the NRC [2] recommendation of 1.00%, tthr for male turkeys for the starting period became 0.82% on a digestible basis, which is close to the 0.81% dthr determined in this trial when using the F:G parameter. An important function of dthr is to provide glycine via threonine dehydrogenase and thre- Figure 6. Broken-line and quadratic analyses of the feed-to-gain ratio (F:G) of male turkeys fed graded levels of digestible threonine (dthr) from 29 to 42 d of age. The minimal dthr requirement for F:G using the broken-line analysis was 0.76% (y = x , R 2 = 0.95). The F:G data were also fitted to a quadratic regression equation (y = x x , R 2 = 0.98). The level of dthr that maximized F:G (i.e., lower asymptote) was calculated to be 0.91% of the diet, with 90% of this value being 0.82%. The first intercept x-value of the broken line (on the plateau) and the quadratic fitted line occurred at 0.81% dthr.

11 394 JAPR: Research Report Figure 7. Broken-line and quadratic analyses of BW gain (BWG) of male turkeys fed graded levels of digestible lysine (dlys) from 29 to 42 d of age. The minimal dlys requirement for BWG using the broken-line analysis was 1.27% (y = x , R 2 = 0.92). The BWG data were also fitted to a quadratic regression equation (y = x x , R 2 = 0.99). The level of dlys that maximized BWG (i.e., upper asymptote) was calculated to be 1.37% of the diet, with 90% of this value being 1.23%. The first intercept x-value of the broken-line (on the plateau) and the quadratic fitted line occurred at 1.32% dlys. Std diet = standard diet. onine aldolase [27] to support the metabolic need for uric acid and synthesis of protein, serine, creatine, and glutathione. Thus, increased AA deamination in high-cp diets increases the need for uric acid, primarily because poultry lack carbamoyl phosphate synthetase activity [19], which plays a key role in the hydrolysis of glutamine and the resulting ammonia [28]. This may increase the need for threonine. In diets with excess protein, the glycine requirement may also be very high, because 1 molecule of glycine is lost with each molecule of uric acid excreted [20]. The loss of glycine might be of particular importance in turkey starter diets, with their current high requirements for CP [2, 3]. It is possible that part of the BW response to supplemental threonine at the first 4 wk of age may be due to a metabolic conversion of threonine to glycine [20]. The requirement levels of dlys in experiment 1 were 1.36% when using BWG (Figure 3) and 1.39% when using F:G (Figure 4). Firman [9] fed Nicholas White male turkeys experimental diets from d 7 to 18, and the dlys requirement determined for optimal BWG was 1.31%. Boling and Firman [6] reported the dlys requirement for Hybrid female poults from 8 to 27 d of age raised in battery cages to be 1.32% for optimal BWG, and 1.34% for optimal feed conversion. Thompson et al. [10] reported the dlys requirement for Nicholas White female poults from 4 to 15 d of age raised in floor pens to be 1.29% for BWG. Few differences were observed when comparing the results of the dlys requirement for starting males and females, supporting the conclusions of Potter and Shelton [28], who suggested that protein requirements are similar

12 Linares et al.: DIGESTIBLE AMINO ACIDS AND MALE TURKEYS 395 between male and female turkeys until about 8 wk of age. However, when the lysine requirements for the starting period were expressed on a total basis, a wide range in requirement values (1.40 to 1.68%) was reported by several authors [29 33]. Warnick and Anderson [34] fed male and female Broad Breast Bronze turkeys from 5 to 17 d and reported the tlys minimum requirement for optimal growth to be 1.68%. However, they used purified diets with high digestibility coefficients, and their recommendation is certainly higher than the range of 1.36 to 1.39% suggested in this study. Tuttle and Balloun [30], using corn- and SBM-based diets, determined the tlys requirement to be 1.50%, and after adjustment to a digestible basis, 85% digestibility coefficient for lysine [unpublished results from our laboratory, 21 26] would be very close to the range observed in this study. With this conversion to the NRC [2] recommendation of 1.60%, tlys for male turkeys for the starting period became 1.36% on a digestible basis, which is exactly the same value determined in this trial using the BWG parameter, and close to 1.39% dlys determined when using the F:G parameter. In experiment 2, the dthr requirements for male turkeys from 29 to 42 d was estimated to be 0.72% using BWG (Figure 5) and 0.76% using F:G (Figure 6). Firman and Guaiume [11] reported that dthr levels between 0.76 and 0.81% were required for male poults from 3 to 6 wk of age to reach optimal growth performance and feed conversion, which agrees with the results of this trial. However, Kidd et al. [19] reported that the level of dietary tthr needed to support adequate BWG and feed conversion in the same period was 0.88% for British United Turkeys Figure 8. Broken-line and quadratic analyses of feed-to-gain ratio (F:G) of male turkeys fed graded levels of digestible lysine (dlys) from 29 to 42 d of age. The minimal dlys requirement for F:G using the broken-line analysis was 1.29% (y = x , R 2 = 0.98). The F:G data were also fitted to a quadratic regression equation (y = x x , R 2 = 0.97). The level of dlys that maximized F:G (i.e., low asymptote) was calculated to be 1.39% of the diet, with 90% of this value being 1.25%. The first intercept x-value of the broken line (on the plateau) and the quadratic fitted line occurred at 1.36% dlys. Std diet = standard diet.

13 396 JAPR: Research Report male turkeys, which seems lower than the results of this experiment when an 82% digestibility coefficient for a typical turkey feed is applied to the diets. Waldroup et al. [35] determined the requirements for total dietary threonine for the same period to be 0.92 and 0.87% for BWG and F:G, respectively, for Nicholas male turkeys, which is consistent with the results of this trial, after the digestibility coefficient was applied to the diets. When the digestibility coefficient to the NRC [2] recommendation of 0.95% tthr for male turkeys from 4 to 8 wk of age was applied, the recommendation became 0.78% on a digestible basis, which is slightly above the values determined in this trial when using the BWG parameter (0.72%) but close to 0.76% dthr determined when using the F:G parameter. The requirement for dlys in experiment 2 was 1.27% when using BWG (Figure 7) and 1.29% when using F:G (Figure 8). Firman [9] fed male Nicholas White poults experimental diets from 23 to 37 d in floor pens and determined the dlys requirement to be 1.17% for optimal BWG, a value significantly lower than the levels observed in this study. Thompson et al. [10] Table 5. Growth performance of male turkeys fed graded levels of digestible lysine (dlys) from 8 to 21 d of age 1,2 Item Feed intake, g BW gain, 3 g Feed:gain, 4 g/g dlys, 5 % b 267 c c ab 274 c c a 288 b bc a 292 ab bc a 299 a b a 301 a b a 299 a b c 269 c a Pooled SEM a c Values in columns with no common superscript differ significantly (P < 0.05). 1 Data are means of 7 replicate pens of 12 poults per pen, except treatment 1.44% dlys, which had 6 replicate pens of 12 poults per pen. 2 Broken-line and quadratic responses (P < ). 3 Regression analysis using the 2-slope broken-line model [16, 17] indicated a requirement of 1.36% dlys, R 2 = Regression analysis using the 2-slope broken-line model [16, 17] indicated a requirement of 1.39% dlys, R 2 = The basal diet contained 1.14% dlys and 0.56% digestible threonine (dthr). The positive control diet contained 1.55% dlys and 0.89% dthr. Table 6. Growth performance of male turkeys fed graded levels of digestible threonine (dthr) from 29 to 42 d of age 1,2 Item Feed intake, g BW gain, 3 g Feed:gain, 4 g/g dthr, 5 % ,541 d 742 e e ,724 c 933 d d ,859 b 1,082 c c ,946 a 1,190 b b ,919 ab 1,184 b ab ,899 ab 1,213 ab a ,888 ab 1,204 ab a ,962 a 1,237 a ab Pooled SEM a e Values in columns with no common superscript differ significantly (P < 0.05). 1 Data are means of 7 replicate pens of 11 poults per pen, except treatment 0.91% dthr, which had 6 replicate pens of 11 poults per pen. 2 Broken-line and quadratic responses (P < ). 3 Regression analysis using the 2-slope broken-line model [16, 17] indicated a requirement of 0.72% dthr, R 2 = Regression analysis using the 2-slope broken-line model [16, 17] indicated a requirement of 0.76% dthr, R 2 = The basal diet contained 1.06% digestible lysine (dlys) and 0.51% dthr. The positive control diet contained 1.55% dlys and 0.89% dthr. observed the same trend and suggested levels of 1.16 and 1.12% dlys when using BWG and F:G, respectively, for Nicholas White hen turkeys from 29 to 40 d. However, Firman and Guaiume [11] obtained the best performance when Nicholas toms were fed 1.33% dlys from 3 to 6 wk of age. Kratzer et al. [36] determined the tlys requirement for male and female turkeys from 4 to 8 wk of age to be 0.96%, whereas Hurwitz et al. [32] determined the tlys requirement for male turkeys for the same period to be 1.12%, based on carcass content and maintenance. Balloun and Phillips [37] found the tlys requirement for both sexes to be 1.55% for the first 6 wk of age, and Tuttle and Balloun [30] recommended 1.40% tlys for male turkeys from 4 to 8 wk of age. When the coefficient of digestibility of a typical corn and SBM diet was applied to the tlys results, the requirement determined by Balloun and Phillips [37] was closer to the results of the current study. With this conversion to the NRC [2] recommendation of 1.50% tlys for male turkeys from 4 to 8 wk of age, it became 1.27% on a digestible basis, which is exactly the same value determined in this trial when using

14 Linares et al.: DIGESTIBLE AMINO ACIDS AND MALE TURKEYS 397 Table 7. Growth performance of male turkeys fed graded levels of digestible lysine (dlys) from 29 to 42 d of age 1,2 Item Feed intake, g BW gain, 3 g Feed:gain, 4 g/g dlys, 5 % ,674 d 996 d c ,816 c 1,093 c c ,825 bc 1,130 c b ,847 bc 1,162 bc ab ,865 bc 1,196 ab a ,888 b 1,206 ab a ,888 b 1,204 ab a ,962 a 1,237 ab ab Pooled SEM a d Values in columns with no common superscript differ significantly (P < 0.05). 1 Data are means of 7 replicate pens of 11 poults per pen, except treatment 1.36% dlys, which had 6 replicate pens of 11 poults per pen. 2 Broken-line and quadratic responses (P < ). 3 Regression analysis using the two-slope broken-line model [16, 17] indicated a requirement of 1.27% dlys, R 2 = Regression analysis using the two-slope broken-line model [16, 17] indicated a requirement of 1.29% dlys, R 2 = The basal diet contained 1.06% dlys and 0.51% digestible threonine (dthr). The positive control diet contained 1.55% dlys and 0.89% dthr. the BWG parameter and close to the 1.29% dlys determined when using the F:G parameter. CONCLUSIONS AND APPLICATIONS 1. The use of digestible AA and IP to formulate diets for turkeys is increasing, necessitating the determination of digestible AA requirements. 2. On the basis of the results of these 2 experiments, the requirement for dlys from 8 to 21 d for male turkeys was estimated to be 1.36% when using BWG and 1.39% when using F:G, whereas the requirement for dthr was estimated to be 0.74% when using BWG and 0.81% when using F:G for the same period, with the ratio of dthr to dlys being For the next phase, from 29 to 42 d, the requirement for dlys for male turkeys was estimated to be 1.27% when using BWG and 1.29% when using F:G, and the requirement for dthr was estimated to be 0.72% when using BWG and 0.76% when using F:G for the same period, with the ratio of dthr to dlys being REFERENCES AND NOTES 1. USDA Livestock and Poultry: World Market and Trade. Circular Series DL&P 2-06, October Foreign Agricultural Service, Washington, DC. 2. NRC Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC. 3. Agri Stats Inc Live Production Analysis Manual. Agri Stats Inc., Fort Wayne, IN. 4. Boling, S. D., and J. D. Firman Digestible sulfur amino acid requirement of starting turkeys. Poult. Sci. 76: Boling, S. D., and J. D. Firman A low-protein diet for turkey poults. Poult. Sci. 76: Boling, S. D., and J. D. Firman Digestible lysine requirement of female turkeys during the starter period. Poult. Sci. 77: Firman, J. D., and S. D. Boling Ideal protein in turkeys Poult. Sci. 77: Moore, D. T., K. Baker, and J. D. Firman Digestible sulfur amino acid requirement for male turkeys to five weeks of age. J. Appl. Poult. Res. 10: Firman, J. D Digestible lysine requirements of male turkeys in their first 6 weeks. Int. J. Poult. Sci. 3: Thompson, K. A., E. Blair, K. A. Baker, and J. D. Firman Digestible lysine requirement for hen turkeys from 0 to 6 weeks of age. Int. J. Poult. Sci. 3: Firman, J. D., and E. A. Guaiume Practical reduced protein diets for broilers and turkeys. In Proc. Annu. Nutr. Conf., The Poultry Federation, Rogers, AR. 12. Kamyab, A., and J. D. Firman Digestible threonine requirement of female Nicholas poults during starter period. J. Appl. Poult. Res. 9: Nicholas Turkeys, Lewisburg, WV. 14. Microsoft Corporation, Redmond, WA. 15. SAS Institute SAS/STAT User s Guide. Version 8. SAS Inst. Inc., Cary, NC. 16. Robbins, K. R., A. M. Saxton, and L. L. Southern Estimation of nutrient requirements using brokenline regression analysis. J. Anim. Sci. 84(E-Suppl.):E155 E Vedenov, D., and G. M. Pesti A comparison of methods of fitting several models to nutritional response data. J. Anim. Sci. 86: Ketelaars, E. H The effects of housing conditions on energy utilization of poultry. Pages in Energy Metabolism in Farm Animals: Effects of Housing, Stress and Disease. M. W. A. Verstegen and A. M. Henken, ed. Kluwer Academic Press, Boston, MA. 19. Kidd, M. T., P. R. Ferket, and J. D. Garlich Dietary threonine responses in growing turkey toms. Poult. Sci. 77: Lehmann, D., M. Pack, and H. Jeroch Effects of dietary threonine in starting, growing, and finishing turkey toms. Poult. Sci. 76: Pierson, E. E. M., L. M. Potter, and R. D. Brown Jr Amino acid digestibility of dehulled soybean meal by adult turkeys. Poult. Sci. 59:

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