Optimal sulfur amino acid to lysine ratio for weaned pigs fed antibiotic-free diets and raised under clean and unclean conditions

Abstract Text: Unsanitary production conditions can stimulate an immune response leading to increased sulfur amino acids (SAA) maintenance needs and consequently the SAA to Lys ratio, especially under antibiotic-free feeding regimen. Two 14-d experiments were conducted to determine the optimum SAA:Lys ratio in piglets when reared under clean or unclean condition and fed antibiotic-free diets. For each experiment, 90 mixed-sex pigs (Duroc x [Yorkshire x Landrace]; initial average BW of 7.3 ± 0.6 kg) weaned at 21±1 d with 6 replicates of 3 pigs per pen were used. The basal diet was corn-wheat-soybean meal-based (1.18% SID Lys; 51% SID SAA:Lys). Diets 2 to 5 were the basal supplemented with 4 graded levels of DL-Met (55, 60, 64, and 68% SID SAA:Lys). Piglets were allowed free access to feed and water. In Exp. 1, piglets were raised in a clean room that was previously disinfected and washed weekly, whereas in Exp. 2, piglets were introduced into a room previously occupied by other pigs and was not disinfected. In addition, manure slurry from a sow herd was spread (5 kg per pen) on d 0 and 7 of the study and the room was not cleaned throughout the study. Blood was collected on d 0 and 14 for measurement of plasma urea nitrogen (PUN). On d 14 one pig per pen was slaughtered to collect jejunal tissue for measurement of villus height (VH), crypt depth (CD), and VH:CD. In both experiments quadratic broken-line model was used to estimate optimum SAA:Lys ratio. The highest average daily gain was at SAA:Lys ratio of 60% (279 g) in Exp 1 and 64% (305 g) in Exp 2. Increasing SAA:Lys ratio linearly and quadratically increased (P < 0.05) VH and VH:CD in Exp. 1 and 2. In Exp. 2, increasing SAA:Lys ratio linearly reduced (P< 0.05)  by 18% average daily feed intake and linearly and quadratically decreased PUN. Based on performance parameters the optimum SAA:Lys ratio was 62 and 61% for piglets raised under clean and unclean conditions, respectively. However, VH and VH:CD estimates were 60% and 64% SAA:Lys ratio under clean and unclean conditions, respectively. Hence SAA:Lys ratio for gut health was higher under unclean conditions.

Keywords: pigs, sanitation, sulfur amino acids