Two 14-day experiments, each with 90 (Duroc × [Yorkshire × Landrace]; 7.3 ± 0.6 kg) piglets, were conducted to determine the optimum sulfur amino acid (SAA) to lysine (Lys) ratio (SAA:Lys) for piglets when reared under clean or unclean sanitary conditions using performance and non-performance response criteria. Piglets were randomly assigned to the following dietary treatments. The basal diet contained 1.18% standardized ileal digestible (SID) Lys, and the SAA:Lys was 52%. In diets 2 to 5, the basal diet was supplemented with 4 graded levels of dl-Met to make SAA:Lys of 56%, 60%, 64% and 68%. In Exp. 1, piglets were housed in disinfected clean room. In Exp. 2, piglets were housed in a room previously occupied by other pigs and was not disinfected. On the last day, blood was collected to measure plasma urea nitrogen (PUN) and one pig per pen was euthanized to collect jejunal tissue to measure villus height (VH), crypt depth (CD), and VH:CD. In Exp. 1, increasing SAA:Lys linearly and quadratically increased VH and VH:CD (P < 0.05). In Exp. 2, increasing SAA:Lys linearly increased (P < 0.05) VH and VH:CD and linearly and quadratically decreased PUN (P < 0.05). Estimated PUN and VH-based optimum SAA:Lys requirements for clean and unclean sanitary condition were 60%, 63% and 66%, respectively.
Keywords: Amino acid ratios; Gut morphology; Lysine; Methionine; Pigs; Sanitary condition.