Effect of arginine supplementation on the morphology and function of intestinal epithelia and serum concentrations of amino acids in pigs exposed to heat stress.

The exposure of pigs to heat stress (HS) appears to damage their intestinal epithelia, affecting the absorption of amino acids (AAs). Arg is involved in the restoration of intestinal epithelial cells but HS reduces Arg intake. The effect of dietary supplementation with Arg on the morphology of intestinal epithelia, AA transporter gene expression, and serum concentration (SC) of free AAs in HS pigs was analyzed. Twenty pigs (25.3 ± 2.4 kg body weight) were randomly assigned to two dietary treatments: Control (0.81% Arg), wheat-soybean meal diet supplemented with l-Lys, l-Thr, dl-Met, and l-Trp, and the experimental diet where 0.16% free l-Arg was supplemented to a similar Control diet (+Arg). All pigs were individually housed and exposed to HS, fed ad libitum with full access to water. The ambient temperature (AT), recorded at 15-min intervals during the 21-d trial, ranged on average from 29.6 to 39.4 °C within the same day. Blood samples were collected on day 18 at 1600 hours (AT peak); serum was separated by centrifugation. At the end of the trial, five pigs per treatment were sacrificed to collect samples of mucosa scratched from each small intestine segment. The expression of AA transporters in intestinal mucosa and the SC of AAs were analyzed. Villi height (VH) was higher (P < 0.01) in the duodenum, jejunum, and ileum but the crypt depth did not differ between the Control and the +Arg pigs. Supplementation of l-Arg increased the mRNA coding for the synthesis of the cationic AA transporter b0,+ (P < 0.01) and the neutral AA transporter B0 (P < 0.05) in the duodenum by approximately 5-fold and 3-fold, respectively, but no effect on mRNA abundance was observed in the jejunum and ileum. The supplementation of l-Arg increased serum Arg, His, Met, Thr, Trp, and urea (P < 0.05) and also tended to increase Val (P < 0.10) but did not affect Ile, Lys, Leu, and Phe. These results indicate that supplementing 0.16% l-Arg to the Control diet may help to improve the function of the small intestine epithelium, by increasing the VH, the abundance of AA transporters, and the SC of most indispensable AAs in pigs exposed to HS conditions. However, the lack of effect of supplemental Arg on both Lys SC and weight gain of pigs suggests that increasing the Lys content in the +Arg diet might be needed to improve the performance of HS pigs.