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.

Dietary protein-bound or free amino acids differently affect intestinal morphology, gene expression of amino acid transporters, and serum amino acids of pigs exposed to heat stress.

Pigs exposed to heat stress (HS) increase body temperature in which can damage the intestinal epithelia and affect the absorption and availability of amino acids (AA). Protein digestion and metabolism further increase body temperature. An experiment was conducted with six pairs of pigs (of 47.3 ± 1.3 kg initial body weight) exposed to natural HS to assess the effect of substituting dietary protein-bound AA by free AA on morphology and gene expression of intestinal epithelial and serum concentration (SC) of free AA. Treatments were: high protein, 21.9% crude protein (CP) diet (HShp) and low protein, 13.5% CP diet supplemented with crystalline Lys, Thr, Met, Trp, His, Ile, Leu, Phe, and Val (HSaa). The HShp diet met or exceeded all AA requirements. The HSaa diet was formulated on the basis of ideal protein. Pigs were fed the same amount at 0700 and 1900 hours during the 21-d study. Blood samples were collected at 1700 hours (2.0 h before the evening meal), 2030 hours, and 2130 hours (1.5 and 2.5 h after the evening meal). At the end, all pigs were sacrificed to collect intestinal mucosa and a 5-cm section from each segment of the small intestine from each pig. Villi measures, expression of AA transporters (y+L and B0) in mucosa, and SC of AA were analyzed. Ambient temperature fluctuated daily from 24.5 to 42.6 °C. Weight gain and G.F were not affected by dietary treatment. Villi height tended to be larger (P ≤ 0.10) and the villi height:crypt depth ratio was higher in duodenum and jejunum of pigs fed the HSaa diet (P < 0.05). Gene expression of transporter y+L in jejunum tended to be lower (P < 0.10) and transporter B0 in the ileum was lower (P < 0.05) in HSaa pigs. Preprandial (1700 hours) SC of Arg, His, Ile, Leu, Thr, Trp, and Val was higher (P < 0.05), and Phe tended to be higher (P < 0.10) in HShp pigs. At 2030 hours (1.5 h postprandial), serum Lys, Met, and Thr were higher in the HSaa pigs (P < 0.05). At 2130 hours (2.5 h), Arg, His, Ile, Phe, and Trp were lower (P < 0.05); Met was higher (P < 0.05); and Lys tended to be higher (P < 0.10) in HSaa pigs. In conclusion, feeding HS pigs with low protein diets supplemented with free AA reduces the damage of the intestinal epithelia and seems to improve its absorption capacity, in comparison with HS pigs fed diets containing solely protein-bound AA. This information is useful to formulate diets that correct the reduced AA consumption associated with the decreased voluntary feed intake of pigs under HS.