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United States Department of Agriculture

Agricultural Research Service


item Parr, T
item Kerr, Brian
item Baker, D

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2003
Publication Date: 5/1/2004
Citation: Parr, T.M., Kerr, B.J., Baker, D.H. 2004. Isoleucine requirement for late-finishing (87 to 100 kg) pigs. Journal of Animal Science. 82:1334-1338.

Interpretive Summary: There is a dearth of information regarding isoleucine (Ile) requirements of finishing pigs, due mainly to the misconception that it is prevalent in common feed ingredients. Available research in this area is primarily older, and although this in itself is not a precursor to making it outdated, other factors cause the research to be less applicable to modern pig production. 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 fed to finishing pigs and the desired concentration of these amino acids in feeding programs for optimal production and minimal nitrogen excretion, is paramount. This information is especially critical since from 150 to 250 pounds of body weight, a pig consumes approximately 70% of its total feed, and consequently, excretes the greatest quantity of manure. This research determined that the true digestible isoleucine requirement of rapidly growing, high-lean-gain pigs from 80 to 120 kg agrees closely with the NRC (1998) factorial estimate of 0.89 g/Mcal for barrows and gilts. Plasma urea-nitrogen results suggested that the isoleucine requirement for late-finishing gilts may be higher than that for late-finishing barrows. Research results described in this report provides nutritionists at universities, feed companies, and swine production units vital data on empirical research methodology on how to clearly define the isoleucine needs of late-finishing swine to properly formulate their diets to optimize growth performance and ultimately to minimize nitrogen excretion.

Technical Abstract: 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 (85 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 digestibility trials in ileal-cannulated pigs and cecectomized roosters. Experiment 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 df 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 Exp. 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 experiments suggest that the factorial requirement estimate of 0.30% true digestible Ile for high-lean late-finishing pigs suggested by the National Research Council Subcommittee on Swine Nutrition is accurate.

Last Modified: 09/20/2017
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