Healthy newly weaned pigs require more tryptophan to maximize feed intake if they are susceptible to Escherichia coli K88 ☆ P. Trevisi a , E. Corrent b , S. Messori a , L. Casini a , P. Bosi a, ⁎ a DIPROVAL, University of Bologna, Reggio Emilia, Italy b Ajinomoto Eurolysine S.A.S., 75017 Paris, France article info abstract 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 first week feed intake increased with Trp in MUC4 +/+ pigs (P b 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 first week (P b 0.05). The higher Trp to Lys ratio increased average daily weight gain in the first week (P b 0.01) and in the whole trial (P b 0.05). Growth performance was not affected by the genotype for MUC4. 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 body weight gain in the three weeks post-weaning. In the first week post-weaning pigs of the genotype MUC4 +/+ require more Trp than the MUC4 -/- pigs to maximize feed intake, when they are free from diseases and are kept in optimal sanitary conditions. © 2010 Elsevier B.V. All rights reserved. Keywords: Pig Weaning Tryptophan Enterotoxigenic E. coli MUC4 1. Introduction The enterotoxigenic Escherichia coli K88ac (ETEC) is the pathogen most frequently isolated in piglets and associated with colibacillosis. The susceptibility to colibacillosis depends on the presence of receptors for the fimbriae of ETEC in pig intestine. The susceptibility to ETEC is traditionally assessed post mortem, but now it is known that the gene involved is strictly linked to the MUC4 gene, and that the polymorphism for this gene can be a useful marker (Jensen et al., 2006). In ETEC challenged pigs this susceptibility can also disclose interactions between the diet and the phenotype. In fact the susceptible pigs in general show lower average daily gain (ADG), higher immune response against ETEC, higher fecal ETEC excretion, more days in diarrhea, and, often, shortened intestinal villi, as compared to not susceptible subjects (Bosi et al., 2004). Furthermore susceptible ETEC challenged pigs had a higher tryptophan requirement, as compared with not-susceptible challenged subjects (Trevisi et al., 2009). However it is not known if the requirement of tryptophan is affected by the susceptibility to ETEC also when pigs are normally reared, without challenge. Livestock Science 134 (2010) 236–238 ☆ This paper is part of the special issue entitled “11th International Symposium on Digestive Physiology of Pigs”. ⁎ Corresponding author. Tel.: +39 0522 290508; fax: +39 0522 290523. E-mail address: paolo.bosi@unibo.it (P. Bosi). 1871-1413/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2010.06.151 Contents lists available at ScienceDirect Livestock Science journal homepage: www.elsevier.com/locate/livsci