Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2005
Publication Date: 11/1/2005
Citation: Dean, D.W., Southern, L.L., Kerr, B.J., Bidner, T.D. 2005. Isoleucine requirement of 80- to 120-kilogram barrows. Journal of Animal Science. 83:2543-2553. Interpretive Summary: Crystalline amino acids have become economical for supplementation into many practical swine diets. To optimize these dietary amino acid additions, there is a need for an accurate estimation of the fourth limiting amino acid, which is isoleucine according to the National Research Council in corn-soybean meal diets fed to late-finishing pigs. The National Research Council requirement for isoleucine is based off ideal amino acid ratios. However, there is little empirical data in the literature estimating the actual true ideal digestible isoleucine requirement for late-finishing pigs. The use of alternative protein sources such as red blood cells, which is deficient in isoleucine, has also created a need to know precisely the isoleucine requirement and to evaluate the interrelationships of the branched chain amino acids. Based on data obtained in these experiments, the true ideal digestible isoleucine requirement for 80- to 120-kg barrows for maximizing feed intake, growth, feed efficiency, and kilograms of lean is not less than 0.34%, or 12.90 mg isoleucine/g body weight gain, in a corn diet containing 5% blood cells. In contrast, the requirement may not be greater than 0.24% in finishing barrows fed a corn-soybean meal diet. Plasma urea nitrogen is not a good measure of the isoleucine requirement due to effects of isoleucine on feed intake. Data would suggest that isoleucine is not a limiting nutrient in formulation of low crude protein, corn-soybean meal diets for late finishing barrows. Further research is needed to evaluate the optimal branched-chain amino acid balance and the maximum level of red blood cells that can be fed to pigs. Research results described in this report provides nutritionists at universities, feed companies, allied industries, and swine production facilities data on how to define the isoleucine needs of finishing pigs to formulate diets necessary to optimize growth performance and subsequently minimize nitrogen losses into the environment.
Technical Abstract: Six experiments were conducted to validate an Ile-deficient diet and to determine the Ile requirement of 80- to 120-kg barrows. Experiment 1 had five replications and Exp. 2 to 6 had four replications per treatment; all replicates had four crossbred barrows each (initial BW were 93, 83, 85, 81, 81, and 88 kg). In Exp. 1, pigs were fed a corn-soybean meal diet (C-SBM) or a corn-5% blood cell (BC) diet with or without 0.26% supplemental Ile (C-BC or C-BC+Ile) in a 28-d growth assay. On d 14, pigs receiving the C-BC diet were taken off experiment due to a severe decrease in ADFI. Growth performance was not different for pigs fed C-SBM or C-BC+Ile (P = 0.36) over the 28-d experiment. In Exp. 2, pigs were fed the C-BC diet containing 0.24, 0.26, 0.28, 0.30, or 0.32% true ileal digestible (TD) Ile for 7 d in an attempt to estimate the Ile requirement using plasma urea nitrogen (PUN) as the response variable. Because of incremental increases in ADFI as TD Ile increased, PUN could not be used to estimate the Ile requirement. In Exp. 3, pigs were fed the C-BC diet containing 0.28, 0.30, 0.32, 0.34, or 0.36% TD Ile. Daily gain, ADFI, and G:F were increased linearly (P < 0.01) as Ile was increased in the diet. Even though there were no effects of TD Ile concentration on 10th rib fat depth or LM area, kilograms of lean was increased linearly (P < 0.01) as TD Ile level increased. In Exp. 4, pigs were fed a C-SBM diet containing 0.26, 0.31, or 0.36% TD Ile. There were no differences in ADFI or ADG, however G:F was increased linearly (P = 0.02) with the response primarily to the 0.31% Ile. In Exp. 5, pigs were fed 0.24, 0.27, 0.30, 0.33 or 0.36% TD Ile in a C-SBM diet. There were no differences in growth performance; however, average backfat, total fat, and percent fat were increased quadratically (P < 0.10) by the addition of Ile. In Exp. 6, pigs were fed a 0.26% TD Ile C-SBM diet with or without crystalline Leu and Val in an attempt to simulate the branched chain AA balance of a C-BC diet. There were no differences in ADFI or ADG, but G:F was increased (P < 0.09) when Leu and Val were added. In summary, the Ile deficiency of a C-BC diet can be corrected by the addition of Ile, and the PUN method is not suitable when assessing the Ile requirement due to dramatic changes in ADFI. The TD Ile requirement for 80- to 120-kg barrows for maximizing growth performance and kilograms of lean is not less than 0.34% in a C-BC diet, but may be as low as 0.24% in a C-SBM diet.