Determination of the optimum standardised ileal digestible sulphur amino acids to lysine ratio in weaned pigs challenged with enterotoxigenic Escherichia coli

This experiment tested the hypothesis that pigs challenged with an enterotoxigenic strain of E. coli (ETEC) would require a higher sulphur amino acids (SAA) to Lys ratio (SAA:Lys). Pigs (n = 120) weighing 7.4 ± 0.52 kg (mean ± SD) and weaned at 27 d (Pietrain genotype, mixed sex) were stratified into 1 of 6 treatments based on weaning weight, sex and genotype for the F4 fimbria receptor (n = 20). Five diets were formulated with increasing ratios of standardised ileal digestible (SID) sulphurSAA:Lys. Pigs were housed in pens of 4 during an adaptation period of 6 d after which time pigs were housed individually. Pigs fed different SID SAA:Lys levels were infected with ETEC (5 mL, 1.13 × 108 CFU/mL, serotype O149:K91:K88) on d 8, 9, and 10 after weaning. The sixth diet, which contained 0.55 SID SAA:Lys and corresponded to current NRC recommendations, was allocated to 2 groups of pigs either with or without ETEC infection, and was considered as the infected or non-infected control group respectively. Pigs were fed Phase 1 diets (10.2 MJ NE, 1.2% SID Lys) ad libitum until d 15 after weaning. Phase 2 diets (10.2 MJ NE, 1.1% SID Lys) were fed ad libitum for the following three weeks. Diets did not contain any antimicrobial compounds. Corrected SID SAA:Lys determined based on analyzed amino acid content and the respective standardised ileal digestibility of ingredients were found to be 0.47, 0.55, 0.61, 0.69 and 0.77 for Phase 1 diets, and 0.47, 0.55, 0.63, 0.71 and 0.78 for Phase 2 diets. Following infection, oedema disease was diagnosed in all groups including the non-infection control group, therefore data from non-infected pigs were combined with pigs infected and fed 0.55 SAA:Lys for analysis of production and plasma data. There were no dietary effects of SID SAA:Lys on days with diarrhoea or faecal shedding of F4 ETEC (P > 0.05). Overall, average daily gain (ADG), feed intake and G:F were optimised at 0.71 (SE = 0.073), 0.73 (SE = 0.065) and 0.68 (SE = 0.090) SID SAA:Lys, respectively. For pigs infected with ETEC and not provided with antimicrobial compounds, and under conditions of the current study, it is suggested that the SID SAA:Lys lies above the current NRC recommendation of 0.55 for pigs after weaning.