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We recently demonstrated that in utero heat stress (IUHS) alters future tissue accretion in pigs, but whether this is a conserved response among species, is due to the direct effects of heat stress (HS) or mediated by reduced maternal feed intake (FI) is not clear. Study objectives were to compare the quantity and rate of tissue accretion in rats exposed to differing in utero thermal environments while eliminating the confounding effect of dissimilar maternal FI. On d3 of gestation, pregnant Sprague-Dawley rats (189.0±5.9g BW) were exposed to thermoneutral (TN; 22.2±0.1°C; n=8), or HS conditions (cyclical 30 to 34°C; n=8) until d18 of gestation. A third group was pair-fed to HS dams in TN conditions (PFTN; 22.2±0.1°C; n=8) from d4 to d19 of gestation. HS increased dam rectal temperature (p=0.01; 1.3°C) compared to TN and PFTN mothers, and reduced FI (p=0.01; 33%) compared to TN ad libitum fed controls. Although litter size was similar (p=0.97; 10.9 pups/litter), pup birth weight was reduced (p=0.03; 15.4%) in HS compared to PFTN and TN dams. Two male pups per dam [n=8 in utero TN (IUTN); n=8 IUHS; n=8 in utero PFTN (IUPFTN)] were selected from four dams per treatment based on similar gestation length, and body composition was determined using dual-energy x-ray absorptiometry (DXA) on d26, d46, and d66 of postnatal life. Whole-body fat content increased (p=0.01; 11.2%), and whole-body lean tissue decreased (p=0.01; 2.6%) in IUPFTN versus IUTN and IUHS offspring. Whole-body composition was similar between IUHS and IUTN offspring. Epididymal fat pad weight increased (p=0.03; 21.6%) in IUPFTN versus IUHS offspring. In summary and in contrast to pigs, IUHS did not impact rodent body composition during this stage of growth; however, IUPFTN altered the future hierarchy of tissue accretion.

Proper insulin homeostasis appears critical for adapting to and surviving a heat load. Further, heat stress (HS) induces phenotypic changes in livestock that suggest an increase in insulin action. The current study objective was to evaluate the effects of HS on whole-body insulin sensitivity. Female pigs (57 ± 4 kg body weight) were subjected to two experimental periods. During period 1, all pigs remained in thermoneutral conditions (TN; 21°C) and were fed ad libitum. During period 2, pigs were exposed to: (i) constant HS conditions (32°C) and fed ad libitum (n = 6), or (ii) TN conditions and pair-fed (PFTN; n = 6) to eliminate the confounding effects of dissimilar feed intake. A hyperinsulinemic euglycemic clamp (HEC) was conducted on d3 of both periods; and skeletal muscle and adipose tissue biopsies were collected prior to and after an insulin tolerance test (ITT) on d5 of period 2. During the HEC, insulin infusion increased circulating insulin and decreased plasma C-peptide and nonesterified fatty acids, similarly between treatments. From period 1 to 2, the rate of glucose infusion in response to the HEC remained similar in HS pigs while it decreased (36%) in PFTN controls. Prior to the ITT, HS increased (41%) skeletal muscle insulin receptor substrate-1 protein abundance, but did not affect protein kinase B or their phosphorylated forms. In adipose tissue, HS did not alter any of the basal or stimulated measured insulin signaling markers. In summary, HS increases whole-body insulin-stimulated glucose uptake. Published version

The metabolic consequences of heat stress (HS) are atypical (i.e. hyperinsulinemia) considering the animal's nutritional status and a compromised intestinal barrier may initiate the pathophysiologi...

Heat stress (HS) jeopardizes human and animal health and reduces animal agriculture productivity; however, its pathophysiology is not well understood. Study objectives were to evaluate the direct effects of HS on carbohydrate and lipid metabolism. Female pigs (57 ± 5 kg body weight) were subjected to two experimental periods. During period 1, all pigs remained in thermoneutral conditions (TN; 20°C) and were ad libitum fed. During period 2, pigs were exposed to: (1) constant HS conditions (32°C) and fed ad libitum (n = 7), or (2) TN conditions and pair-fed (PFTN; n = 10) to minimize the confounding effects of dissimilar feed intake. All pigs received an intravenous glucose tolerance test (GTT) and an epinephrine challenge (EC) in period 1, and during the early and late phases of period 2. After 8 days of environmental exposure, all pigs were killed and tissue samples were collected. Despite a similar reduction in feed intake (39%), HS pigs tended to have decreased circulating nonesterified fatty acids (NEFA; 20%) and a blunted NEFA response (71%) to the EC compared to PFTN pigs. During early exposure, HS increased basal circulating C-peptide (55%) and decreased the insulinogenic index (45%) in response to the GTT. Heat-stressed pigs had a reduced T3 to T4 ratio (56%) and hepatic 5'-deiodinase activity (58%). After 8 days, HS decreased or tended to decrease the expression of genes involved in oxidative phosphorylation in liver and skeletal muscle, and ATGL in adipose tissue. In summary, HS markedly alters both lipid and carbohydrate metabolism independently of nutrient intake. Published version

Climate change, and thermal stress (i.e., heat and cold) in particular, is a key limiting factor to efficient animal production and negatively impacts health and development during postnatal life. In addition, thermal stress (especially heat stress) during in utero development can permanently alter postnatal phenotypes and negatively affect future animal performance. The global effects of thermal stress on animal agriculture will likely increase as climate models predict more extreme weather patterns in most animal-producing areas. While the ultimate consequence of heat and cold stress is similar (reduced productivity and compromised animal welfare), their mechanism(s) of action substantially differs. Predictably, many of the metabolic and physiological effects of heat and cold stress are biologically contrasting; however, both are homeorhetically orchestrated to prioritize survival at the cost of agriculturally productive purposes. Consequently, thermal stress threatens global food security and this is especially apparent in developing countries. There is an urgent need for the scientific community to develop mitigation strategies to increase production of high-quality animal protein for human consumption during the warm summer months.