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United States Department of Agriculture

Agricultural Research Service

Title: Determining the optimal isoleucine:lysine ratio for 10- to 22-kg and 24- to 39-kg pigs fed diets containing non-excess levels of leucine

Authors
item Htoo, John -
item Zhu, Cuilan -
item Huber, Lee-Anne -
item DE Lange, Cornelius -
item Quant, Anthony -
item KERR, BRIAN
item Cromwell, Gary -
item Lindemann, Merlin -

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2014
Publication Date: August 1, 2014
Citation: Htoo, J., Zhu, C., Huber, L., De Lange, C., Quant, A., Kerr, B.J., Cromwell, G., Lindemann, M. 2014. Determining the optimal isoleucine:lysine ratio for 10- to 22-kg and 24- to 39-kg pigs fed diets containing non-excess levels of leucine. Journal of Animal Science. 92:3482-3490.

Interpretive Summary: Optimum amino acid intake is important to optimize growth and feed efficiency in pigs. Although there has been a large amount of research conducted on the lysine requirement in pigs, there has been limited research conducted on the standaridized isoleucine to lysine ratio to be utlized in feed formulations. Providing an optimal isoleucine to lysine ratio in diets fed to pigs will not only maximize animal performance, but because environmental issues with nitrogen losses from swine operations, understanding this amino acid relationship is paramount in low crude protein diets. Based on data obtained in these experiments, the optimum standardized ileal digestible isoleucine:lysine ratio is approximately 51% for 10 to 22 kg pigs, and 54% for 24 to 39 kg pigs fed diets containing non-execss levels of leucine. 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 pigs to formulate diets necessary to optimize growth performance and subsequently minimize nitrogen losses into the environment.

Technical Abstract: Three 21-day experiments were conducted to determine the optimum standardized ileal digestible (SID) isoleucine:lysine (Ile:Lys) ratio in 10 to 22 kg and 24 to 39 kg pigs. In Exp. 1, 144 pigs (initial body weight = 10.2 kg) were assigned to 6 diets with 6 pens per treatment. Diets 1 to 5 were formulated to contain 5 graded SID Ile:Lys (44, 51, 57, 63 and 70%), 1.18% SID Leu and 0.90% SID Lys (Lys being second limiting). Diet 6 (diet 5 with added Lys) was formulated (1.06% SID Lys) as a positive control. Pigs fed diet 6 had higher average daily gain (ADG), gain:feed (G:F) and lower plasma urea nitrogen (PUN) than pigs fed diet 5 (P < 0.02), indicating that Lys was limiting in diets 1 to 5. Final BW, ADG and average daily feed intake (ADFI) increased (linear and quadratic, P < 0.001) while G:F and PUN at d 21 were not affected (P > 0.10) by dietary Ile:Lys. Overall, ADG and ADFI were highest for pigs fed diet 2 (51% SID Ile:Lys). In Exp. 2, 216 pigs (initial body weight = 9.6 kg) were assigned to 9 diets with 6 pens per treatment. Diets 1 to 4 contained 0.40, 0.47, 0.54 and 0.61% SID Ile, respectively, and 1.21% SID Lys; diets 5 to 8 contained 0.72, 0.84, 0.96 and 1.08% SID Lys, respectively, and 0.68% SID Ile. Diet 9 was high in both Ile and Lys (0.68% SID Ile and 1.21% SID Lys). All diets contained 1.21% SID Leu. The ADG and G:F increased (linear and quadratic, P < 0.001) as SID Ile:Lys increased (diets 1-4 and 9). The ADG and G:F increased (linear, P < 0.001) as SID Lys increased (diets 5-9). The PUN at d 21 decreased (linear, P < 0.001) by increasing dietary Ile:Lys. The SID Ile:Lys to optimize ADG was 46% by curvilinear plateau or exponential regression. For G:F, the optimal SID Ile:Lys was 47 and 51% by curvilinear plateau and exponential regressions, respectively. In Exp. 3, 80 pigs (initial body weight = 24.0 kg) were allotted to 5 treatments with 4 pigs per pen. Diets 1 to 5 were formulated to contain 5 graded SID Ile:Lys (39, 46, 53, 61, and 68%), 1.17% SID Leu and 0.91% SID Lys (Lys being second limiting). Final body weight and ADG increased (linear and quadratic, P < 0.05), and ADFI increased (linear, P = 0.047) as SID Ile:Lys increased. Using ADG and G:F, the optimum SID Ile:Lys was 54 and 53%, respectively by curvilinear plateau and exponential regression. The PUN was minimized at 53 and 59% SID Ile:Lys by curvilinear plateau and broken line regression. Overall, the average optimum SID Ile:Lys was approximately 51% for 10 to 22 kg pigs, and 54% for 24 to 39 kg pigs fed diets containing non-excess levels of Leu.

Last Modified: 9/29/2014
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