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Two experiments were conducted to evaluate the effects of two dietary levels of lysine and four dietary levels of threonine in a factorial arrangement on broiler growth, carcass traits, and immunity. In both experiments, 120 broilers were allocated to each of 56 floor pens (6,720 total broilers). In Experiment 1, two levels of lysine (1.10 and 1.20% of diet) and four levels of threonine (0.68, 0.74, 0.80, and 0.86% of diet) were fed to broilers from 1 to 18 d of age in a sorghum-peanut meal diet. Body weight gain, feed:gain, mortality, and cellular and humoral immunity were measured. In Experiment 2, all broilers received a common basal diet up to 18 d of age. Experimental diets were fed from 18 to 34, 34 to 44, and 44 to 54 d of age. Two levels of lysine [100 and 105% of NRC (1994) recommendations] and four levels of threonine [83, 92, 100, and 108% of NRC (1994) recommendations] were included in the experimental diets for each age group (seven replications per treatment). The diets consisted of wheat (soft), corn gluten meal, soybean meal, and meat and bone meal Weight gain, feed:gain, mortality, and carcass traits were measured at 54 d of age. In Experiment 1, increasing dietary lysine from 1.10 to 1.20% from 1 to 18 d in broilers improved (P < 0.001) BW gain (453 vs 488 g) and feed:gain (1.39 vs 1.33). No interactions between lysine and threonine were observed in Experiment 1. Differences in immune parameters or mortality were not observed. In Experiment 2, an interaction in 18 to 54 d weight gain occurred with the highest gain in broilers receiving dietary lysine and threonine levels equivalent to 100 and 83%, respectively, of NRC (1994) or lysine and threonine at levels of 105% and 100% of NRC (1994), respectively (P < or = 0.05). Supplemental lysine (105% of the 1994 NRC) improved (P < or = 0.01) 18 to 54 d feed:gain (2.30 vs 2.26). No differences in mortality occurred. Supplemental lysine increased preslaughter weight (P < or = 0.05), but differences in carcass yield were not observed. Breast fillet yields were the highest (P < or = 0.03) in broilers receiving 100% of NRC lysine and 83 or 92% of NRC threonine or 105% of NRC lysine and 100 or 108% of NRC threonine. In conclusion, additional lysine improved feed:gain independent of threonine from 1 to 54 d of age. However, lysine and threonine interact to increase weight gain and breast fillet yields.

One hundred eight high-lean-growth gilts (34.4 kg BW) were used to determine the dietary lysine requirement to maximize growth, carcass characteristics, and protein accretion from 34 to 72.5 kg BW. The experiment was a randomized complete block design; initial BW served as the blocking factor. Six dietary treatments were included, ranging from .54 to 1.04% (.10% increments) digestible lysine (.69 to 1.25% total lysine). Pigs were housed in pens of three, with six replicate pens per treatment. Pig weights and feed consumption were collected weekly to calculate ADG, ADFI, and gain:feed (G/F). Initially, five pigs were slaughtered to determine baseline carcass composition. When the mean weight for pigs in a pen reached 55 and 72.5 kg, one pig per pen was randomly selected and slaughtered for carcass measurements. The right side of each carcass was ground twice and sampled to determine carcass composition and tissue accretion rates. Average daily gain was increased by dietary lysine from 34 to 55 kg (linear, P < .01), from 55 to 72.5 kg (linear, P < .10), and from 34 to 72.5 kg (linear, P < .01). Although ADFI from 34 to 55 and from 55 to 72.5 kg was not influenced by dietary lysine, ADFI for the entire experiment tended to decrease (quadratic, P < .10) as digestible lysine increased. Increased dietary lysine resulted in improved G/F from 34 to 55 kg (linear, P < .01) and from 55 to 72.5 and 34 to 72.5 kg (quadratic, P < .01). Average backfat thickness was not influenced by dietary lysine at 55 kg but decreased (linear, P < .05) as dietary lysine increased at 72.5 kg. At 55 kg, longissimus muscle area was larger (linear, P < .05) for gilts fed increased digestible lysine. However, longissimus muscle area was similar for all treatments at 72.5 kg. Gilts fed increased digestible lysine had greater CP accretion from 34 to 55 kg (linear, P < .01), 55 to 72.5 kg (linear, P < .05; quadratic, P < .10), and from 34 to 72.5 kg (quadratic, P < .05). Based on the feed intake observed in this study, the high-lean-growth gilt requires at least 22 g/d total lysine intake from 34 to 72.5 kg to maximize CP accretion.

Three experiments were conducted to determine the effect of reducing NE, by adding dietary fiber in Exp. 1 and 2 and decreasing dietary fat in Exp. 3, of low-CP, crystalline amino acid (CAA)-supplemented diets for finishing pigs on growth performance and carcass characteristics. In Exp. 1 and 2, 64 barrows (Exp. 1) or gilts (Exp. 2) were allotted to four treatments with four replicates of four pigs each. Average initial and final BW were 74 and 117 kg in Exp. 1 and 74 and 102 kg in Exp. 2. The following diets were fed in Exp. 1: 1) corn-soybean meal (C-SBM); 2) low-CP (-3.5%), supplemented with CAA; 3) CAA + rice hulls (CAA+RH; NE equal to Diet 1); and 4) CAA+RH+OIL (NE equal to Diet 2). Experiment 2 was similar to Exp. 1, except RH were replaced with wheat middlings (WM), oil was replaced with dry fat, and the CP was decreased by 3.1% in the low-CP diets. In both experiments, serum urea-N (SUN, corrected for initial SUN by covariance analysis) was higher (P<.10) for pigs fed C-SBM than for pigs fed any other diet. In Exp. 1, barrows fed CAA+RH had lower hot carcass weight, percentage muscle, fat-free lean (FFLEAN), lean gain per day, retained energy (RE) in FFLEAN, and lean:fat ratio than barrows fed C-SBM, along with less FFLEAN than barrows fed CAA+RH+OIL. Barrows fed CAA+RH had smaller longissimus muscle areas than barrows fed any other diet, and barrows fed C-SBM had higher dressing percentage and lower percentage total fat than barrows fed any other diet. Barrows fed C-SBM had higher lean:fat ratio and lower total fat than barrows fed CAA. In Exp. 2, gilts fed CAA+WM+FAT had heavier heart weights than gilts fed C-SBM or CAA (P<.10). In Exp. 3, 702 gilts were allotted to six treatments with nine replicates of 13 gilts each. Average initial and final BW were 70 and 110 kg. Gilts were fed two levels of CP (15.5 or 11.7% plus CAA added to meet an ideal amino acid ratio) and three levels of NE (2,650, 2,617, or 2,584 kcal/kg), resulting in a 2x3 factorial arrangement of treatments. Gilts fed 15.5% CP had higher gain:feed ratio than gilts fed 11.7% CP (P<.01). Longissimus depth was greater for gilts fed 15.5% CP than for gilts fed 11.7% CP and was decreased as NE decreased only in gilts fed 11.7% CP (CP effect, P<.09; NE linear effect, P<.04; CP x NE effect, P<.01). Gilts fed the diet with 2,617 kcal NE had lighter carcasses and less total fat, fat gain per day, RE, and RE as fat regardless of protein level than gilts fed 2,650 or 2,584 kcal NE/kg (NE quadratic, P<.09). Loin color score increased as NE decreased (linear, P<.06), but longissimus fat depth was increased by the lowest level of NE (NE quadratic effect, P<.09). Overall, the reduction of NE in low-CP, CAA-supplemented diets did not affect growth performance and was not an effective means of reducing fat in finishing pigs.

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