Heat stress of gilts around farrowing causes oxygen insufficiency in the umbilical cord and reduces piglet survival

Late gestating sows are susceptible to high ambient temperatures, possibly causing farrowing complica-tions and reducing piglet survival. This experiment aimed to quantify in the days leading up to farrowing the impact of sow heat stress (HS) on farrowing physiology and survival of the piglets. Pregnant primi-parous sows (gilts) were allocated to either thermoneutral control (CON, n = 8; constant 20 degrees C) or cyclical HS conditions (n = 8; 0900 h to 1700 h, 30 degrees C; 1700 h to 0900 h, 28 degrees C) from d 110 of gestation until far-rowing completion. Gilt respiration rate, skin temperature and rectal temperature were recorded daily, and farrowing duration was quantified by video analyses. Blood samples were collected from the piglet umbilical vein at birth. At 48 h of age, piglet growth was quantified by morphometric analyses. The ther-mal exposure model induced HS and respiratory alkalosis in the gilts, as indicated by increased respira-tion rate, rectal temperature, skin temperature (all P < 0.001), plasma cortisol (P = 0.01) and blood pH (P < 0.001). Heat-stressed gilts took longer to start expelling placentae (P = 0.003), although the active farrowing duration was not significantly different between treatments. Stillbirth rates were higher in the HS group (P < 0.001), with surviving piglets at birth having lower umbilical vein partial pressure of oxygen (P = 0.04), oxygen saturation rate (P = 0.03) and tending to have increased lactate concentrations (P = 0.07). At birth, piglet skin meconium staining scores were greater in the HS group (P = 0.022). At 48 h of age, piglets from the HS group had reduced small intestinal length (P = 0.02), reduced jejunal crypt depth (P = 0.02) and lighter absolute brain weight (P = 0.001). In contrast, piglet BW, growth rate, relative organ weight and small intestinal mucosal barrier function did not change between treatments. Collectively, these findings demonstrated gilt HS during late gestation caused farrowing complications and reduced the umbilical oxygen supply to the piglets at parturition, leading to increased risks of piglet stillbirth with implications on impaired neonatal survivability and development.(c) 2022 The Authors. Published by Elsevier B.V. on behalf of The Animal Consortium. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This experiment examined the impact of heat stress on late gestating sows and found that it caused farrowing complications and reduced piglet survival.