Heat stress affects the serum concentrations of free amino acids in growing pigs

Abstract Text: Exposure to heat stress (HS) may impair the intestinal epithelia of pigs resulting in decreased digestive and absorptive capacity. The serum concentration (SC) of free AA in pigs can be used as indicator of their availability. This study was conducted with 12 pigs (29.0 ± 2.8 kg initial BW) distributed into 2 groups to analyze the SC of free AA and some AA metabolites in pigs exposed to HS conditions. The treatments were: pigs housed under natural HS conditions with no ambient temperature control (23.6 to 37.6° C, HS); and pigs housed at thermo-neutral (TN) conditions (24 ± 2 °C), pair-fed with their HS counterparts (TN_pf). The room ambient temperature and relative humidity were recorded during the whole study. All pigs received a typical wheat-SBM diet. Blood samples were collected at both the absorptive (2.5 h post-prandial) and post-absorptive (10 h post-prandial) phase. The absorptive SC of free Arg, Leu, Lys, Phe, Thr, and Trp were lower (P<0.05), and His and Val tended to be lower (P<0.10) in HS pigs. Also, the SC of Ala, Pro, Ser, and Tyr tended to be lower (P<0.10). No effect of HS was observed in the SC of Ile, Met, Asn, Asp, Gln, Glu, and Gly. The post-absorptive SC of free Arg, His, and Met, as well as Asn, Gln, and Tyr were higher (P<0.05) in HS pigs, but Ala was lower and Pro tended to be lower (P<0.10) in HS pigs. The absorptive SC of carnosine, Orn, and Tau were lower (P<0.05), and Cit, cystathionine, and urea tended to be lower (<0.10) in HS pigs. The post-absorptive SC of 3-methyl-His, anserine, OH-Lys, and OH-Pro increased (P = 0.05), and Cit tended to increase (P = 0.10), but carnosine and sarcosine (P < 0.05) decreased in HS pigs. These results show a marked and differential effect of HS on the SC of AA, especially that of Arg, His, Met, and Thr. These data indicate that HS negatively affects the digestive and absorptive capacities of pigs, and that the metabolism of some AA is modified in pigs to counteract the negative effects of the HS

Keywords: Pigs, heat stress, serum amino acids