ABSTRACT This study investigated the effects of dietary L-valine (Val) supplementation and sanitary conditions with lipopolysaccharide injection on growth performance, immune response, and intestinal bacterial profiles and metabolites in weaned pigs. Thirty-two weaned pigs (6.98 ± 0.47 kg) were randomly assigned to treatments in a 2 × 2 factorial arrangement based on dietary Val levels and sanitary conditions (low or high). The pigs were fed either a basal diet containing the standard levels of Val suggested by (NRC), (2012) or a basal diet supplemented with 0.1% L-Val. A room designated as a high sanitary room was washed weekly, whereas the designated low sanitary room was not washed throughout the experiment and 5 kg of manure from the nursery pig barn was spread on the pen floors on day 1. All data were analysed using a mixed procedure of SAS, with the individual pen as the experimental unit. The pigs raised in low sanitary conditions exhibited a lower (p < 0.05) average daily gain, average daily feed intake, and gain-to-feed ratio and a higher (p < 0.05) incidence of diarrhoea than those raised in high sanitary conditions during the 14-d experimental period. The pigs in the low sanitary group also had a lower (p < 0.05) concentration of butyrate in the jejunum and a higher (p < 0.05) concentration of NH3-N in the colon than those in the high sanitary group. Dietary Val supplementation was reduced (p < 0.05) plasma interleukin (IL)-1β and IL-1 receptor antagonist concentrations as well as isovalerate and NH3-N concentrations in the colon, regardless of sanitary conditions. Interactions between dietary Val supplementation and sanitary conditions were observed in the abundances of mRNA-encoding β-defensins 113, 125 and 129 (p < 0.05). In conclusion, dietary Val supplementation beneficially modulates inflammatory responses and microbial metabolites regardless of sanitary conditions while transcriptional levels of β-defensins are regulated by dietary Val supplementation in a manner dependent on housing hygiene conditions.
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