Impact of two heat stress models on performance and immune parameters of weaned pigs

Abstract Text: A study was conducted to compare the impact of 2 heat stress models on weaned pig performance.  A total of 38 pigs were ranked by litter and weight at weaning, randomly assigned to 3 individual rooms (2 pens/room, 6-7 pigs/pen), and provided a common nursery diet for 4 wk.  Pigs were then subjected to 1 of 3 thermal treatments; 1) thermoneutral (TN; 25°C); 2) constant heat (CH, 35°C); or 3) variable heat (VH, 40°C 5h, 25°C 19h) for 7 cycles (d 1 to 7).  Pigs and feeders were weighed weekly prior to, and daily during, heat stress to determine ADG, ADFI, and G:F.  Rectal temperature, thermal images to determine skin surface temperature, and respiration rate were recorded daily during heat stress.  Fecal samples were collected on d -1, 1, 3, and 7 and blood and intestinal tissue were collected on d 1, 3, and 7 in relation to the start of heat stress.  Body weight was similar on d -1 among treatment groups but was decreased 9% in VH by the end of the study (P = 0.04).  During the 7 d heat stress ADG was highest in TN (750.0, 508.6, and 491.7 g/d in TN, CH, and VH, respectively; P = 0.04), ADFI was reduced in both CH and VH (P = 0.001), but G:F was similar among treatments.  Rectal and skin surface temperatures and respiration rate were elevated in both heat stress groups compared to TN, and VH was higher than CH during heat stress (P < 0.0001).  Fecal propionic acid was lower overall (P = 0.001) and butyrate was decreased on d 1 in CH and VH compared to TN (6.2, 3.8, and 3.8% in TN, CH, and VH, respectively; P = 0.04).  Plasma cortisol was highest in VH, intermediate in CH, and lowest in TN on d 7 of heat stress (P = 0.01).  Desquamation was observed in the jejunum of VH pigs on d 3 of heat stress.  Additionally, jejunal villus height was reduced on d 1 and 3 of heat stress, and villus height:crypt depth ratio was lower in VH and CH on d 3 of heat stress compared to TN (P = 0.05).  In conclusion, both CH and VH were acceptable models to negatively impact measures of health and performance; however, the response to VH was more severe and better represents the type of stress found in a production setting.

Keywords: heat stress, pig