Interpretive Summary: 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.
By: Jackie Walling
Transportation is inevitable in the production industry and as global temperature rises, heat heightens stress experienced by animals in route to a new destination. A recent article published in the May 2018 Issue of the Journal of Animal Science delves into evaluating how early life thermal stress (ELTS) on newly weaned piglets affects thermoregulation, stress response, and intestinal health later on when piglets are simultaneously placed under heat stress (HS) conditions and simulated transport. The combination of weaning, HS, and transport significantly compromises the health of newly weaned piglets making management of those factors a necessity. Researchers hypothesized prior HS exposure could improve future thermotolerance.
On days 7-9 after farrowing, 12 sows bearing first litters were equally split into three ELTS exposure groups: early life thermoneutral (ELTN - 25.4⁰C /heat lamp), early life cold stress (ELCS - 25.4⁰C/no heat lamp), and early life heat stress (ELHS - cycling 32-38⁰C/heat lamp). Average Daily Gain (ADG) was calculated by taking weight of the piglets on day 6, 10, and weaning. Thermal measurements (respiration rate (RR), skin temperature (TS), and rectal temperature (TR)) were recorded for each sow and three chosen piglets (per sow), four times a day, on days 6-9. Core Temperatures (TC) were recorded starting on day 13. At weaning, the three selected piglets per sow were weighted and herded into a simulated transport trailer. There, they underwent cycling HS for 8 hours while experiencing stress factors associated with traveling (mixing, isolation, feed/water withdrawal). In this situation, motion is not simulated during this time. Piglets were then housed in TN conditions to account for ADG, average daily feed intake (ADFI), and behavioral observations. On day 8 after simulation, piglets were euthanized and a section of jejunum collected for analysis.
Thermoregulation measures (RR, TR, TS, and sow rectal temperature (sowTR)) during ELTS were all elevated in the ELHS group compared to ELCS and ELTN groups. Differences between ELCS and ELTN were minimal, but TS tended to be cooler during ELCS than in ELTN. Most measurements peaked day 8 though sowTR was greatest on days 8 and 9. During simulated transport, ELHS saw the greatest TC and TS increase overall with a pattern of increasing temperature peaking at 7 and 6 hours, respectively.
Growth performance showed initial BW, weaning weight, overall ADG, and ADG (ELTS phase) similar across treatments with ELHS showing a slight reduction in overall ADG and ADG (ELTS phase). After transport simulation, ELHS saw the greatest BW loss, a reduction in ADFI and circulating HSP70, and an increase in circulating cortisol compared to the other two groups. Behavior observations such as lying and sitting increased across the board as time progressed. Histology of the jejunum reported no differences in villus height or crypt depth for all groups, but ELHS did show a decreasing number of goblet cells per villi.
Previous poultry and rodent studies indicate early exposure to HS boosts future thermotolerance, but this study showed ELHS increased hyperthermic responses and impeded thermotolerance in pigs. Consequences resulted in reduced performance, increased stress response, and decreased intestinal health contributing to future negative implications on performance. Lengthening the time of ELTS and changing the age of exposure could potentially alter the results of this study. To read the full article, go to the Journal of Animal Science.