Isoleucine requirement for late-finishing (87 to 100 kg) pigs

Three pig trials were carried out to determine the true digestible Ile requirement for maximal weight gain and minimal plasma urea nitrogen (PUN) of late-finishing (87 to 105 kg) pigs. In Exp. 1, an Ile-deficient basal diet was developed and confirmed to be markedly deficient in Ile, yet fully efficacious when fortified with surfeit Ile. This diet contained corn and dried red blood cells (RBC) as Ile sources, and was analyzed to contain 10.5% CP, 0.25% Ile, and 0.63% lysine; ME was calculated to be 3,475 kcal/kg. True digestibility of Ile in the basal diet was 88% based on previous digestibility trials in ileal-cannulated pigs and cecectomized roosters. Experiment 2 was a growth trial that involved five graded levels of crystalline Ile supplementation (0.02%) to generate five dose levels of true digestible Ile (0.25 to 0.33%), Diets 1 through 5, respectively. Gain and feed efficiency showed a linear response to incremental doses of Ile (P = 0.003 and 0.036, respectively), with an apparent plateau at 0.31% true digestible Ile. In Exp. 3, a replicated 5 x 5 Latin square, five barrows (Square 1) and five gilts (Square 2) were used in five 4-d feeding periods, with five levels of true digestible Ile (0.22 to 0.30%). Using feed intake as a covariate, a linear decrease in PUN occurred in gilts (8.9, 8.6, 8.0, 7.0, and 5.5; P = 0.004) and in gilts and barrows combined (9.5, 9.2, 9.2, 8.5, and 7.6; P = 0.006) as Ile increased incrementally. The PUN results for barrows (10.5, 10.0, 10.2, 9.9, and 9.7) were not affected by dietary Ile (P = 0.417). The results of these experiments suggest that the factorial requirement estimate of 0.30% true digestible Ile for high-lean, late-finishing pigs suggested by the NRC Subcommittee on Swine Nutrition is accurate.