270
Effects of increasing standardized ileal digestible threonine:lysine ratio on performance of weaned pigs challenged with Escherichia coli K88
An experiment was conducted to evaluate the effects of dietary standardized ileal digestible (SID) threonine:lysine (Thr:Lys) ratio on performance and plasma urea nitrogen (PUN) concentration in piglets subjected to an Escherichia coli K88 (E. coli K88) challenge and fed antibiotic-free diets. Thirty five individually housed mixed-sex pigs (Duroc x [Yorkshire x Landrace]) with an initial BW of 7.3 ± 0.5 kg and weaned at 21 ± 1 d were randomly assigned to 5 dietary treatments with 7 pig replicates per treatment. Dietary treatments contained increasing levels of SID Thr:Lys ratios (55, 59, 63, 67 and 71%). Diets were corn-wheat-soybean meal based with a constant SID Lys of 1.18% that was set to be the second limiting AA but adequate in other AA. Pigs had ad libitum access to feed and water for the 14 d. On d 8, piglets were orally challenged with 6 mL of E. coli K88 (2 x 109 cfu/mL). Body weights and feed disappearance were recorded weekly to determine ADG, ADFI and G:F. Blood samples were collected on d 0, 7 and 14 to determine PUN. During the pre-challenge period (d 0-7), increasing SID Thr:Lys increased ADG (102, 113, 119, 138 and 100 g/d; quadratic, P ≤ 0.05) and G:F (0.64, 0.65, 0.77, 0.75 and 0.68; quadratic, P ≤ 0.05), with the highest being 67% and 63%, for ADG and G:F, respectively. The curvilinear-plateau regression estimated that ADG and G:F was maximized at a SID Thr:Lys of 65% and 66%, respectively. During the post-challenge period (d 8-14), there were no effects of increasing SID Thr:Lys on PUN, ADFI, and G:F which suggest that the E. coli challenge used in this experiment was insufficiently sensitive to activate immune system stimulation in weaned pigs. During the overall period (d 0-14), increasing the SID Thr:Lys trended to increase (P = 0.08) the ADG and the greatest responses in ADG and G:F were achieved with a dietary SID Thr:Lys ratio of 67%.
Keywords: threonine:lysine, Escherichia coli, piglets