Early life thermal stress: Impact on future thermotolerance, stress response, behavior, and intestinal morphology in piglets exposed to a heat stress challenge during simulated transport

Authors: Johnson, Jay; AARDSMA, MATTHEW - Purdue University; DUTTLINGER, ALAN - Purdue University; KPODO, KOUASSI - Purdue University

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2018
Publication Date: 4/4/2018
Citation: Johnson, J.S., Aardsma, M.A., Duttlinger, A., Kpodo, K. 2018. Early life thermal stress: Impact on future thermotolerance, stress response, behavior, and intestinal morphology in piglets exposed to a heat stress challenge during simulated transport. Journal of Animal Science. 96(5):1640-1653. https://doi.org/10.1093/jas/sky107.
DOI: https://doi.org/10.1093/jas/sky107

Interpretive Summary: Transporting newly weaned pigs can reduce well-being, and ambient temperature may contribute to piglets total stress load. Unfortunately, newly weaned pigs are often transported through wide temperature ranges and for extended durations. Therefore, it’s imperative that management strategies are developed to improve piglet well-being during incidences of simultaneous production stress and heat stress. Prior heat stress exposure may improve future thermotolerance and provide protection against unrelated stressors. Because heat stress and weaning cause intestinal injury, it is possible that early life heat stress exposure may improve future piglet well-being in response to weaning and transport during heat stress. Consequently, because cold stress acclimation is characterized by increased heat production, it is possible that early life cold stress would decrease piglets’ ability to adapt to a future heat stress challenge. Therefore, study objectives were to evaluate the effects of early life thermal stress on the future thermoregulation, productivity, and intestinal morphology of newly weaned piglets exposed to simulated transport and heat stress. We hypothesized that early life heat stress would be beneficial and early life cold stress would be detrimental to future piglet well-being when exposed to a heat stress challenge during simulated transport compared to early life thermoneutral exposure. However, contrary to our hypothesis, we determined that pigs subjected to early life heat stress had increased body temperature during heat stress that likely contributed to a greater stress response and intestinal damage when compared to early life cold stress and early life thermoneutral pigs. Although these data have improved our understanding of the impact of early life heat stress on the future response of piglets, the mechanisms by which early life heat stress reduces thermotolerance have yet to be elucidated.

Technical Abstract: Study objectives were to evaluate the impact of early life thermal stress (ELTS) on thermoregulation, stress, and intestinal health of piglets subjected to a future heat stress (HS) challenge during simulated transport. Approximately 7 d after farrowing, 12 first parity gilts and their litters were exposed to thermoneutral (ELTN; 25.4 ± 1.1ºC w/ heat lamps; n = 4), HS (ELHS; cycling 32-38ºC; n = 4), or cold stress (ELCS; 25.4 ± 1.1ºC w/ no heat lamps; n = 4) for 3 d post-farrowing, and then all piglets were exposed to TN conditions (25.3± 1.9ºC w/ heat lamps) until weaning. During the ELTS period, respiration rate (RR), rectal temperature (TR) and skin temperature (TS) of three mixed-sex piglets per dam were monitored daily (0800, 1200, 1600, 2000h). At 13 ± 1.3 d of age, temperature recorders were implanted intra-abdominally into all piglets. At weaning (20.0 ± 1.3 d of age), all piglets were bled and then herded up a ramp into a simulated transport trailer and exposed to HS conditions (cycling 32-38ºC) for 8 h. During the 8 h simulated transport, core body temperature (TC) and TS were assessed in 15 min intervals. After the simulated transport, piglets were unloaded from the trailer, bled, weighed, and then housed individually in TN conditions (28.5 ± 0.7ºC) for 7 d. During this time, ADFI and ADG were monitored, blood samples were taken on d 1, 4, and 7, and piglets were video-recorded to assess behavior. Piglets were sacrificed on d 8 post-simulated transport and intestinal morphology was assessed. Data were analyzed using PROC MIXED in SAS 9.4. In the ELTS period, piglet TR was increased overall (P = 0.01) in ELHS (39.77 ± 0.05°C) compared to ELTN (39.34 ± 0.05°C) and ELCS (39.40 ± 0.05°C) litters. During simulated transport, TC was greater (P = 0.02) in ELHS (40.84 ± 0.12°C) compared to ELTN (40.49 ± 0.12°C) and ELCS (40.39 ± 0.12°C) pigs. Following simulated transport, body weight loss was greater (P = 0.01; 40%) for ELHS compared to ELTN and ELCS pigs and ADFI was reduced (P = 0.05; 28.6%) in ELHS compared to ELTN pigs. Sitting behavior tended to be increased (P = 0.06; 47.4%) in ELHS vs. ELCS or ELTN pigs. Overall, circulating cortisol was greater for ELHS (P = 0.01; 38.8%) compared to ELCS and ELTN pigs. Goblet cells per villi were reduced (P = 0.02; 20%) in the jejunum of ELHS vs. ELCS and ELTN pigs. In summary, ELHS increased the future stress response and reduced thermotolerance of piglets compared to ELCS and ELTN.