Effects of heat stress on growth performance of finishing pigs

This study was conducted to investigate effects of high humidity under high temperature conditions on rectal te.mperature, growth performance, blood profiles, and immune responses of finishing pigs. In a randomized complete block design [block = initial body weight (BW)], 120 finishing pigs (initial BW = 49.62 ± 1.15 kg) were allotted to 2 temperature treatments [thermal neutral condition [temperature-humidity index (THI) 68: 23°C, 35%] and heat stress condition (THI 87: 33°C, 80%); 5 pig/pen; 12 replicates/treatment] during 2 weeks. The diet based on corn-soybean meal was formulated to meet or exceed the nutrient requirements of finishing pigs. Pigs had access to feed and water ad libitum. The rectal temperature of one pig per replicate was measured daily throughout the experimental period to monitor changes in body temperature. Blood samples were collected from 1 pig per replicate at the beginning and end of the experiment. Measurements were growth performance [BW, average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio], blood profiles [the number of white blood cells (WBC), red blood cells, hemoglobin, hematocrit, and platelet] measured by an automated hematology analyzer calibrated for porcine blood, and immune responses (cortisol, tumor necrosis factor-alpha, interleukin-6, interleukin-1beta, and transforming growth factor-beta1) by the ELISA kits. The daily rectal temperature of pigs under THI 87 was higher (p < 0.05) during the overall experimental period than those under THI 68. Pigs under THI 87 had lower (p < 0.05) ADG and ADFI than those under THI 68. The number of WBC of pigs under THI 87 was decreased (p < 0.05) compared with those under THI 68. In conclusion, this study suggests that exposure to high humidity in combination with high temperature has a negative impact on growth performance of finishing pigs.