Body temperature of pigs exposed to heat stress conditions: effect of dietary protein level

Heat stress (HS) reduces feed intake and increases body temperature (BT) in pigs. Increased dietary protein content may correct HS-related reduced amino acid intake, but it may further increase BT. The effect of dietary protein level on BT of HS pigs was analyzed with 9-ileal cannulated pigs (61.7 ± 2.7 kg BW). A thermometer set to register BT at 5-min intervals was implanted into the ileum. There were two treatments: low-protein (10.8%) wheat-free Lys-Thr diet (LP); high-protein (21.6%), wheat-soybean meal diet. The study was conducted in two-10 d periods; d1-d7 for diet adaptation and d8 to d10 for BT data analysis. Pigs were fed at 0600 (morning), 1400 (midday), and 2200-h (evening), same amount each time. Ambient temperature (AT) and relative humidity ranged from 30.1 to 35.4 °C and from 50 to 84%, respectively. Both AT and BT followed a similar pattern; BT did not differ between LP and HP pigs (P > 0.05). Postprandial midday and evening BT was higher than postprandial morning BT (P < 0.05). The BT increment after the midday meal was larger and longer (P < 0.05) than that after the morning and evening meals. The postprandial morning and evening BT increments were longer in the HP pigs. Apparently, the capacity of pigs to dissipate postprandial body heat depends on the accumulated thermal load received before their meals; the thermal load before the morning meal was lower than that before the evening meal. In conclusion, these data show that the dietary protein level has a small effect on the BT of HS pigs, confirm that the effect of AT on BT of HS pigs is stronger than that of dietary protein content, and suggest that the capacity of pigs to dissipate body heat increases under HS conditions. This information may be useful to design better feeding strategies for pigs exposed to HS conditions.