Submitted to: Illinois Swine Day Report
Publication Type: Proceedings
Publication Acceptance Date: April 1, 2002
Publication Date: December 1, 2003
Citation: Parr, T.M., Kerr, B.J., Baker, D.H. 2003. Isoleucine requirement of grower (20 to 50 kg) pigs. Illinois Swine Day Report. p. 5-12.
Interpretive Summary: Most of the research conducted on the isoleucine requirement of pigs was done 30 to 50 years ago involving pigs with limited potential for lean growth. Moreover, validation of isoleucine-deficient assay diets was 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. True isoleucine digestibility was determined to be 89% in the isoleucine-deficient assay diet. Based on maximal weight gain and minimal plasma urea nitrogen, the true digestible isoleucine requirement was determined to be 0.50% of the diet which is somewhat higher than the National Research Council factorial estimate for growing (20 to 50 kg) pigs. 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 growing-finishing swine to properly formulate their diets to optimize growth performance and ultimately to minimize nitrogen excretion.
Three experiments (a validation experiment, a performance experiment and a plasma urea nitrogen experiment) were conducted using an isoleucine (Ile)-deficient basal diet containing red blood cells to determine the true digestible Ile requirement of high-lean grower pigs (20 to 50 kg), so that solid empirical evidence could be used to evaluate the accuracy of the National Research Council (1998) factorial estimate of the Ile requirement. In the first experiment, the basal diet was verified to be markedly deficient in Ile, but when fortified with Ile it was found to be fully efficacious when compared with a 16% CP, corn-soybean meal positive control diet. In the performance experiment, the empirical estimate of the true digestible Ile requirement of 0.50% of the diet was higher than the NRC (1998) factorial estimate of 0.45% for pigs in the grower phase (20 to 50 kg) of growth. Assuming a true Ile digestibility value of 89% for pigs fed a corn-soybean meal diet, the total Ile requirement calculates to be 0.56% of the diet which also exceeds the NRC (1998) estimate of 0.51% of the diet for 20 to 50 kg pigs fed a corn-soybean meal diet. The plasma urea nitrogen study confirmed the performance experiment in that PUN decreased and appeared to reach a nadir at 0.50% true digestible Ile. In conclusion, the true digestible Ile requirement of grower pigs (26 to 42 kg) is approximately 0.50%, which is slightly higher than the NRC (1998) factorial estimate of 0.45% for pigs weighing 20 to 50 kg.