Evaluating the Effects of In Utero Heat Stress on Piglet Physiology and Behavior Following Weaning and Transport

SIMPLE SUMMARY: Transporting weaned piglets from the farrowing house to a nursery or grow/finish site is a common but stressful procedure in United States swine production. Piglets removed from the sow at weaning undergo feed and water withdrawal during transportation, and this stress is further compounded by an abrupt change from a liquid to solid diet upon arrival at their destination. As a result, newly weaned and transported piglets exhibit reduced body weight and signs of dehydration post-transport. Unfortunately, in utero stressors can modify the offspring’s physiological, immune, and behavioral responses during postnatal life and may pre-dispose animals to a greater stress response when exposed to novel postnatal procedures, such as weaning and transport. Therefore, the study objective was to evaluate the effects of in utero heat stress on the behavior and physiology of piglets following weaning and transport. We hypothesized that in utero heat-stressed piglets would exhibit a greater behavioral and physiological stress response following weaning and transportation. Additionally, in utero heat-stressed piglets were expected to show physiological signs of metabolic stress immediately following weaning and transport. It was determined that there was some evidence for altered physiological and behavioral responses among in utero heat stressed piglets compared to in utero thermoneutral piglets following weaning and transport. ABSTRACT: The study objective was to determine whether in utero heat stress (IUHS) affects piglet physiology and behavior following common production practices. A total of 12 gilts were confirmed pregnant and allocated to either heat stress (HS; n = 6) or thermoneutral (TN; n = 6) conditions on day 30–60 of gestation. At weaning (22.5 ± 2.3 days of age), 1 boar and 1 barrow of median weight were selected from each litter and transported for approximately 7 h. Piglets were then blocked into pens (n = 2/pen) by in utero treatment (IUHS (n = 12) or in utero thermoneutral (IUTN, n = 12)) and sexual status (boar (n = 6/in utero treatment) or barrow (n = 6/in utero treatment)). Plasma cortisol, non-esterified fatty acids (NEFA), insulin and glucose were evaluated 1 day prior to transport (pre-transport) and immediately after transport (post-transport). Behavioral data were collected on day 1–7 for 60 min at four different time points each day. In utero heat stressed piglets exhibited reduced cortisol concentrations compared to IUTN piglets immediately post-transport (p = 0.04). Glucose concentrations were not affected by in utero treatment. Insulin concentrations were reduced in IUTN piglets post-transport compared to pre-transport (p = 0.002), but no differences were detected for IUHS pigs. Non-esterified fatty acids tended to be reduced overall for IUHS vs. IUTN pigs (p = 0.08). Overall, IUHS piglets performed more drinking behaviors (p = 0.02) and tended to perform more aggressive behaviors (p = 0.07) than IUTN piglets in the 7 days post-transport. In summary, there was some evidence for altered physiological and behavioral responses among IUHS piglets compared to IUTN piglets following weaning and transport.