Abstract
Heat stress (HS) reduces feed intake and affects the well-being of pigs by increasing their body temperature (BT) and respiration rate (RR). Nitric oxide, an Arg metabolite, helps to dissipate body heat by stimulating blood vasodilation. Because reduced feed intake translates into decreased Arg consumption, the effect of supplementing Arg in the diet on BT and RR was analyzed using 8-ileal cannulated pigs (61.7±2.7 kg BW) exposed to HS. A thermometer set to register BT at 5-min intervals was implanted into the ileum. There were two treatments: control wheat-soybean meal plus free Lys-Thr diet (CON), and the CON diet added with 0.20% free Arg (ARG). The study was conducted in two-6 d periods; d1-d3 for diet adaptation and d4-d6 for BT data analysis. The RR (respirations per min - rpm) was measured in all pigs at 0600-h and 1600-h. Pigs were fed at 0700-h and 1900-h, 900 g/meal. Ambient temperature and relative humidity were: 28.2-to-34.6 °C, 53-to-82%, respectively. Ambient temperature and BT followed a similar pattern every day. There was no interaction in BT and RR between periods. Overall, BT of ARG pigs (40.75°C) was slightly lower (P < 0.05) than in CON pigs (40.71°C). Arg supplementation greatly reduced RR (rpm) regardless of period and day time (P < 0.05): overall (91, 73), period-1 (98, 78), period-2 (85, 68), 0600-h, (68, 52), 1600-h (115, 94), respectively. The RR at 0600-h (60) was lower than at 1400-h (109; P < 0.05) regardless of diet. The reduced RR because of Arg supplementation may be explained as an increased synthesis of nitric oxide probably resulting in both increased vasodilation and dissipation of body heat. In conclusion, although supplemental Arg caused a modest decrease in BT, the large RR reduction may indicate that Arg might help to improve the welfare of HS pigs.