Submitted to: Illinois Swine Day Report
Publication Type: Research Notes
Publication Acceptance Date: November 1, 2003
Publication Date: November 1, 2003
Citation: Parr, T.M., Kerr, B.J., Baker, D.H. 2003. Isoleucine requirement for late-finishing (87 to 100 kg) pigs. Illinois Swine Day Report. p. 10-19.
Interpretive Summary: Research conducted on the isoleucine requirement of pigs is extremely limited and was conducted over 25 years ago involving pigs with limited lean growth potential. Moreover, validation of isoleucine-deficient assay diets were seldom carried out, and often the experimental pigs were limit fed rather than full fed. Lastly, energy and protein levels of assay diets were different from the levels used in practice today and the isoleucine digestibility of the basal diets was not known. Thus, recent estimates of the isoleucine requirement of pigs (National Research Council Subcommittee on Swine Nutrition, 1998) were based on (calculated) factorial estimates rather than on empirical evidence. As environmental issues with nitrogen losses from swine operations becomes more pressing and as the availability of crystalline amino acids becomes more economically viable, understanding amino acid limitations in low crude protein diets and their desired concentration in feeding programs for optimal production and minimal nitrogen excretion, is paramount. Experimentation indicated that a corn-soybean meal-red blood cell diet was determined to be markedly deficient in isoleucine, but fully efficacious when fortified with surfeit isoleucine. The results from this research suggest a requirement estimate of 0.31% true digestible isoleucine for
late-finishing pigs which is similar to that estimated by the 1998 National Research Council. Research results described in this report provides nutritionists at universities, feed companies, and swine production units vital data on how to clearly define the isoleucine needs of finishing swine to properly formulate their diets to optimize growth performance and ultimately to minimize nitrogen excretion.
Three pig trials were carried out to determine the true digestible isoleucine (Ile) requirement for maximal weight gain and minimal plasma urea nitrogen (PUN) of late-finishing pigs. An Ile-deficient basal diet was developed and confirmed to be markedly deficient in Ile, yet fully efficacious when fortified with surfeit Ile (Trial 1). The basal diet contained corn and red blood cells (RBC) as Ile sources, and was analyzed to contain 10.5% CP, 0.25% (Trial 1 and 3) to 0.28% (Trial 2) Ile and 0.63% lysine (Lys); ME was calculated to be 3,475 kcal/kg. Ture digestibility of Ile in the basal diet was 88% based on digestibility trials in ileal-cannulated pigs and cecectomized roosters. Trial 2 was a growth trial that involved five dose levels of true digestible Ile (0.25 to 0.33%). Gain and feed efficiency displayed no response (P < 0.10) to the first incremental dose of Ile, but a single degree-of-freedom contrast comparing diets 1 and 2 to diets 3-5 showed a response (P < 0.05) in gain and gain:feed to incremental doses of Ile, with an apparent plateau at 0.31% true digestible Ile. In Trial 3, a replicated
5 x 5 Latin Square, five barrows (square 1) and five gilts (square 2) utilized five 4-d feeding periods and five levels of true digestible Ile (0.22 to 0.30%). Using feed intake as a covariate, a linear (P < 0.01) decrease in PUN occurred in gilts, and in gilts and barrows combined, as Ile was incremented. The PUN results for barrows were erratic. The results of these trials suggest a requirement estimate of 0.31% true digestible Ile (0.89 g/Mcal) for late-finishing pigs, similar to that estimated by the 1998 National Research Council Subcommittee on Swine Nutrition.