PSXIII-6 - Effects of high humidity under high-temperature conditions on growing pigs

Abstract: Global warming and climate change have become major concerns. These changes have led to more frequent and prolonged heat waves, resulting in economic losses for livestock industry. Pigs are particularly vulnerable to heat stress under high temperatures due to their thick skin layers and limited sweat glands. Panting is a common behavior in pigs to dissipate heat through evaporation, but this process is less effective in high humidity environments. This study was conducted to investigate the effects of high humidity under high temperature conditions on rectal temperature, growth performance, blood profiles, and immune responses of growing pigs. A total of 48 growing pigs [(Landrace × Yorkshire) × Duroc; initial body weight (BW): 23.21 ± 3.77 kg] were randomly assigned to two environmental treatments (2 pigs/pen; 12 replicates/treatment) in a randomized complete block design (block = initial BW): thermal neutral conditions (TN: 23.5℃, 35%) and heat stress conditions (HS: 32.5℃, 80%). Throughout two weeks of experiment, the pigs had ad libitum access to a basal grower diet based on corn and soybean meal. The rectal temperature of each pig was measured daily throughout the experimental period to monitor changes in body temperature. Blood samples were collected from 1 pig per pen at the beginning and end of the experiment. Measurements included 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. Statistical analysis was performed using the general linear model procedure of the SAS program. Experimental unit was a pen. The statistical model included environmental treatment as a main effect and BW as a covariate for rectal temperature, growth performance, blood profiles, and immune responses. During the entire experimental period, the mean rectal temperature was 39.9℃ for TN and 40.5℃ for HS. Pigs under HS had lower (P < 0.05) ADG and ADFI than those under TN. The WBC counts of pigs under HS were decreased (P < 0.05) than those under TN. In contrast, serum cortisol level of pigs under HS were higher (P < 0.05) than those under TN. In conclusion, this study suggests that exposure to high humidity in combination with high temperatures has a negative impact on the growth performance and immune responses of growing pigs.