ARS | Publication request: Isoleucine Requirements and Ratios in Starter (6 to 11 Kg) Pigs

Submitted to: Journal Of Animal Science
Publication Acceptance Date: March 16, 2004
Publication Date: August 1, 2004
Citation: Kerr, B.J., Kidd, M.T., Cuaron, J.A., Bryant, K.L., Parr, T.M., Maxwell, C.V., Campbell, J.M. 2004. Isoleucine Requirements And Ratios In Starter (6 To 11 Kg) Pigs. Journal Of Animal Science. 82:2333-2342.

Interpretive Summary: There are only limited empirical estimates of the isoleucine requirement for starting pigs as estimated in the National Research Council (NRC) Subcommittee on Swine Nutrition, 1998. Because environmental issues with nitrogen losses from swine operations has become more pressing and as the availability of crystalline amino acids become more economically viable, understanding isoleucine limitations in low crude protein diets and its desired concentration in feeding programs for optimal production and minimal nitrogen excretion, is paramount. Results from two experiments show that utilization of red blood cells and crystalline isoleucine in starting pig diets clearly creates an isoleucine deficient diet from which to conduct isoleucine requirement and isoleucine:lysine ratio studies. Requirement data suggests that the apparent digestible isoleucine requirement of 6 to 13 kg pigs appears to be in the range of 0.65 to 0.73%, which is higher than the NRC (1998) estimate of 0.60%. Ratio data suggests that the apparent digestible isoleucine:lysine ratio of these starter pigs is in the range of 0.58 to 0.62%, which is also higher than the NRC (1998) isoleucine:lysine ratio estimate of 0.55%. 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 starting pigs to properly formulate their diets to optimize growth performance and ultimately to minimize nitrogen excretion.

Technical Abstract: Two experiments were conducted to refine the isoleucine (Ile) needs in 6 to 11 kg pigs. In Exp. 1, 1680 pigs, initial BW of 6.6 kg, were fed a 1.25% digestible (d) lysine (Lys) diet containing 7.5% spray dried blood cells with supplemental crystalline Ile (0.06% increments) to generate seven levels of apparent dIle (0.47 to 0.83%). Responses in ADG, ADFI, gain:feed (GF) ratio, and plasma urea nitrogen (PUN) were quadratic (P < 0.01) over the 16-d period. Data was fitted to both a single-slope broken line and a quadratic fit, and when the quadratic response curve was superimposed on the broken line, the points at which the quadratic curve first intersected the plateau of the broken line occurred at 0.70, 0.73, 0.66, and 0.65% dIle for ADG, ADFI, GF, and PUN, respectively. Using the ADG and ADFI obtained at this intersection point results in an estimate of 9.1 mg dIle per gram of weight gain. In Exp. 2, 1840 pigs, initial BW of 6.6 kg, were fed similarly composed diets, except that the dLys was lowered in six diets to 1.10% by the reduction in soybean meal. Crystalline Ile was supplemented at 0.09% increments to generate six levels of dIle (0.37 to 0.83%). A seventh diet contained 1.25% dLys by supplementing the 0.83% dIle diet with 0.19% L-lysine'HCl to verify that 1.10% dLys was deficient for these pigs. Supplementation of Lys to the 0.83% dIle diet (1.10 vs. 1.25% dLys) show that ADG (260 vs. 264 g/d, P = 0.60) and ADFI (359 vs. 343 g/d, P = 0.20) were unaffected, while GF (725 vs. 774 g/kg, P < 0.01) was improved by increasing dietary Lys. Responses in ADG, ADFI, and GF ratio to the first six diets were quadratic (P < 0.01) over the 16-d period. The points at which the quadratic curve first intersected the plateau of the broken line occurred at 0.686, 0.638, and 0.684% dIle for ADG, ADFI, and GF, respectively. Using the ADG and ADFI obtained at this intersection point results in an estimate of 9.9 mg dIle per gram of weight gain. The results of these experiments suggest that although the percentage dIle requirement and dIle:dLys ratio for starter (6 to 11 kg) pigs may be higher than 1998 NRC recommendations, they may be lower than current recommendations when taking gain and feed intake into account.