Serum concentrations of free amino acids in growing pigs exposed to diurnal heat stress fluctuations.

In areas where the ambient temperature (AT) is above the thermo neutral (TN) zone of pigs, significant changes within a 24-h period occur, differently affecting the availability of amino acids (AA) within the same day. An experiment was conducted to analyze the serum concentrations (SC) of free AA in pigs exposed to diurnal variations in AT. Six pigs (27.1 ±1.3kg body weight) implanted with a thermometer to register the body temperature (BT) at 15-min intervals were used. Blood samples were collected on the last 3 d of the 14-d study, at 0700h (lowest AT), 1200h (mild HS), and 1600h (severe HS). The pigs received 1.2kg/d of an AA-supplemented, wheat-soybean meal diet, in two equal meals (0700 and 1900h). The AT and BT, recorded at 0700, 1200, and 1600h was: 30.6, 38.6, 41.1°C, and 38.2, 39.5, 40.3°C, respectively. The BT was significantly correlated (P < 0.001) with the AT. The SC (μM/mL) of Ile, Lys, Met, Val, Ala, Asn, and Pro were higher (P ≤ 0.01); Arg, Phe, Glu, and Tyr tended to be higher (P ≤ 0.10); but Cys was lower (P < 0.05) at 1200h than at 0700h. Lys was higher, Cys and Tyr were lower (P < 0.05), and Ile and Val tended to be higher (P ≤ 0.10) at 1600h than at 0700h. Serum Arg, Ile, Phe, Ala, Asn, Gln, Pro, Ser, and Tyr were lower (P < 0.05), and Leu and Val tended to be lower at 1600h than at 1200h. These data demonstrate that AT directly alters the BT of pigs, and that diurnal variations in AT differently affect their SC and availability of AA for growth.