Healthy newly weaned pigs require more tryptophan to maximize feed intake if they are susceptible to Escherichia coli K88

After challenging piglets with enterotoxigenic Escherichia coli K88 (ETEC), L-tryptophan addition limits the decrease in feed intake and weight gain in ETEC-susceptible subjects. Here we verified whether the susceptibility to ETEC affects the requirement of tryptophan in piglets reared in optimal sanitary conditions and without E. coli K88 challenge. The MUC4 gene was used as a marker to verify the susceptibility, to grouping 36 pigs after weaning, into homozygote for the negative and positive alleles (2 −/− and 2 +/+ pigs per litter). For 21 days pigs were fed using two different diets within each genotype per litter, varied for Trp to Lys ratio (17% or 22%, standardized ileal digestible basis— SID), by a supplementation of 0.5 g/kg L-Trp. In the 1st week feed intake increased with Trp in MUC4+/+ pigs (P<0.05), but not in MUC4−/−. Without Trp addition a trend of decreased feed intake was seen in MUC4+/+ (P=0.094). On average, for the two genotypes, Trp addition increased feed intake in the firstweek (P<0.05). The higher Trp to Lys ratio increased average daily weight gain in the first week (P<0.01) and in the whole trial (P<0.05). Growth performancewas not affected by the genotype forMUC4. The results were also validated by an in vitro test of adhesion of E. coli K88 to the intestinal villi:we confirmed that there is a strong correlation between MUC4 genotype and the phenotype for the presence of ETEC receptor on the intestinal villi. Data confirm that a Trp to Lys ratio of 22% is necessary to maintain the bodyweight gain in the threeweeks post-weaning. In the first week post-weaning pigs of the genotypeMUC4+/+ require moreTrp than theMUC4−/− pigs to maximize feed intake,when they are free from diseases and are kept in optimal sanitary conditions.