The purpose of this investigation was to establish the role biological sex plays in circulating factors following heat stress (HS). Barrows and gilts (36.8 ± 3.7 kg body weight) were kept in either thermoneutral (TN; 20.8 ± 1.6 °C; 62.0% ± 4.7% relative humidity; n = 8/sex) conditions or exposed to HS (39.4 ± 0.6 °C; 33.7% ± 6.3% relative humidity) for either 1 (HS1; n = 8/sex) or 7 (HS7; n = 8/sex) d. Circulating glucose decreased as a main effect of the environment (P = 0.03). Circulating non-esterified fatty acid (NEFA) had an environment × sex interaction (P < 0.01) as HS1 barrows had increased NEFA compared to HS1 gilts (P = 0.01) and NEFA from HS7 gilts increased compared to HS1 gilts (P = 0.02) and HS7 barrows (P = 0.04). Cortisol, insulin, glucagon, T3, and T4 were reduced as a main effect of environment (P ≤ 0.01). Creatinine was increased in HS1 and HS7 animals compared to TN (P ≤ 0.01), indicative of decreased glomerular filtration rate. White blood cell populations exhibited differential patterns based on sex and time. Neutrophils and lymphocytes had an environment × sex interaction (P ≤ 0.05) as circulating neutrophils were increased in HS1 barrows compared to TN and HS7 barrows, and HS1 gilts (P ≤ 0.01) and HS7 barrows had less neutrophils compared to TN barrows (P = 0.01), whereas they remained similar in gilts. In contrast, barrow lymphocyte numbers were similar between groups, but in HS7 gilts they were decreased compared to TN and HS1 gilts (P ≤ 0.04). In total, these data demonstrate that HS alters a host of circulating factors and that biological sex mediates, at least in part, the physiological response to HS.
Keywords: blood; climate change; heat stroke; sex; swine.
Heat stress (HS) negatively impacts efficient pork production; however, the role of biological sex is largely unknown. The objective of this study was to determine the extent to which HS differentially impacted hematological parameters in barrows and gilts. To address this, 3-mo-old barrows and gilts were exposed to ambient temperature (TN) or constant HS for 1 or 7 d. Following the experimental period, blood was collected for analysis of hormones, metabolites, immune cells, and markers of organ damage. Overall, cortisol, insulin, glucagon, T3, and T4 were reduced following HS. Furthermore, 7 d of HS decreased circulating glucose, albeit slightly. Circulating fatty acids had a sex-specific response as HS1 barrows and HS7 gilts were increased compared to their environmental counterparts, though, these changes are minor compared to those expected with a similar feed restriction. HS caused immune system activation in barrows and gilts; however, circulating levels of specific white blood cells were time- and sex-dependent. Barrows appeared more resistant to HS-mediated kidney injury acutely; however, with continued heating, markers of kidney injury were similar between barrows and gilts. In total, these data suggest biological sex regulates some, but not all, aspects of HS-mediated biological changes in pigs.
© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.