Evaluating the Effects of In Utero Heat Stress on Piglet Physiology and Behavior 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.

Impacts of in Utero Heat Stress on Carcass and Meat Quality Traits of Market Weight Gilts

“…Numerous factors are known to contribute to the color of fresh meat products including chronic and acute stress pre-slaughter, glycolytic potential, genetics, among others [ 46 ]. As previously mentioned, IUHS has been associated with energy metabolism [ 4 , 9 , 10 ] and the stress response [ 9 , 11 , 12 ] in swine. However, it appeared such differences did not have any meaningful effect on oxidative stability shown by instrumental display color and TBARS values, nor on the extent of protein denaturation shown by transmission values.…”

“…Differences in performance and carcass composition through IUHS are often attributed to differential energy metabolism, as several studies have observed changes in blood insulin levels and glucose metabolism [ 4 , 9 , 10 ]. Similarly, offspring exposed to IUHS often exhibit increased blood cortisol [ 11 , 12 ], although decreased blood cortisol was observed by Byrd et al [ 9 ] and Maskal et al [ 10 ] following prolonged stress exposure. The level of blood cortisol has been shown to be related to multiple carcass quality attributes such as a positive correlation to carcass weight and backfat thickness and a negative correlation to lean carcass content [ 13 ].…”

Characterizing the postnatal hypothalamic–pituitary–adrenal axis response of in utero heat stressed pigs at 10 and 15 weeks of age

“…Specifically, during exposure to acute stressors (e.g., birth, social stress, handling stress, weaning), an increase in circulating and salivary cortisol 3 – 5 and adrenocorticotropic hormone (ACTH) 6 have been reported for IUHS pigs when compared to in utero thermoneutral (IUTN) pigs. Interestingly, the opposite is true following more prolonged stressors (e.g., transport), whereby circulating cortisol levels are reduced in IUHS compared to IUTN pigs 7 , 8 . In addition to hormonal influences, IUHS increases the incidence of stress-associated behaviors when pigs are exposed to common postnatal production stressors (e.g., weaning and/or transport) 5 , 7 .…”

“…Interestingly, the opposite is true following more prolonged stressors (e.g., transport), whereby circulating cortisol levels are reduced in IUHS compared to IUTN pigs 7 , 8 . In addition to hormonal influences, IUHS increases the incidence of stress-associated behaviors when pigs are exposed to common postnatal production stressors (e.g., weaning and/or transport) 5 , 7 . However, although the aforementioned studies 3 – 8 have been instrumental in identifying how IUHS can impact postnatal measures of swine stress and welfare, none to our knowledge have attempted to elucidate mechanisms that underlie these responses.…”

“…As previously mentioned, IUHS causes alterations in postnatal physiological and behavioral stress responses of pigs 3 – 8 , yet to our knowledge there has not been research conducted to describe HPA axis function in these models. Additionally, IUHS research that has observed altered postnatal physiological and behavioral stress responses has been conducted in relatively young pigs that have not been given time to mature 3 , 5 – 7 , possibly providing time for development of physiology capable of adequately dealing with stressors. Previous studies describing development of mature circadian rhythms have only observed a true rhythm at approximately 3 to 4 months of age 19 , of which previously described IUHS studies only observed effects up to approximately 2 months of age 3 – 8 .…”