Effects of dietary threonine: lysine ratioes and sanitary conditions on performance, plasma urea nitrogen, plasma-free threonine and lysine of weaned pigs

Two 21 d-experiments were conducted to determine the optimum standardized ileal digestible (SID) threonine: lysine ratio (Thr: Lys) for weaned piglets reared under clean (Exp. 1) or unclean (Exp. 2) sanitary conditions and fed antibiotic-free diets. In each experiment, 90 mixed-sex pigs (Duroc x [Yorkshire x Landrace]; initial BW7.2 +/- 0.3 kg) were randomly assigned to 5 dietary treatments each with 6 replicates (3 pigs per pen). The dietary treatments were 5 graded levels of SID Thr: Lys (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 second limiting amino acid. In Exp. 1 and Exp. 2, plasma-free Thr increased (P = 0.05) with increasing dietary SID Thr: Lys. In Exp. 1, the SID Thr: Lys for gain-to-feed ratio (G: F) was optimized at 65%. In Exp. 2, the estimated optimal SID Thr: Lys for overall G: F was 66.5%. In conclusion, an average optimal SID Thr: Lys of 65 and 66.5% could be used to optimize feed efficiency for weaned pigs under clean and unclean sanitary conditions, respectively. (C) 2015, Chinese Association of Animal Science and Veterinary Medicine. Production and hosting by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.