Browsing by Author "Dougherty, Dana Claire"

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    Influence of biological sex and thyroid hormone on skeletal and cardiac muscle metabolism in heat-stressed pigs
    Dougherty, Dana Claire (Virginia Tech, 2025-01-21)
    Heat stress (HS) is a substantial economic burden for the livestock industry, and the problem is expected to increase because of unprecedented warming temperatures caused by climate change. Skeletal muscle, which is the main source of income for the meat industry, is particularly sensitive to HS. Lean tissue accretion declines during HS, in part because of inefficient metabolism and altered metabolic flexibility. The first study examined whether thyroid hormone (TH) administration during HS could maintain metabolic flexibility in HS skeletal and cardiac muscle. Gilts (n=39) were placed in one of five treatment groups: Thermoneutral control (TNC), HS for 1 day (HS1C), HS1 with TH supplementation (HS1TH), HS for 7 days (HS7C), HS7 with TH supplementation (HS7TH). Semitendinosus red skeletal muscle (STR) and right ventricle cardiac muscle (RV) were dissected and snap-frozen for subsequent analysis. Metabolic flexibility (MF; P=0.08) tended to differ between HS1C, HS7C, with HS7TH being the lowest (P < 0.05) in STR. Pyruvate oxidation significantly differed with the lowest in HS1TH and highest in HS7TH in RV muscles (P < 0.05) but metabolic flexibility did not differ. However, citrate synthase (CS) and cytochrome C oxidase (COX) activity did not differ between treatments. The second experiment investigated the difference in skeletal muscle metabolism between gilts and barrows. Pigs (n=8/sex) were exposed to TNC, HS1, or HS7 environments. Skeletal muscle samples were used to analyze in vivo metabolism. Barrows tended (P=0.09) to be more MF than gilts even though no changes in mitochondrial enzyme activity were observed. However, gilts differed between environmental treatments regarding CS activity (P=0.03). Blood serum from the treated pigs was placed on skeletal muscle cell cultures. Metabolic flexibility between the in vivo muscle samples and the cell cultures was similar. In vitro culture at 37°C recapitulated the in vivo metabolic flexibility pattern. When the cell culture temperature was maintained at 41°C, MF was the lowest in cultures that received HS7 blood serum. In vitro males incubated at 41°C displayed an increase in CS and COX activity (P<0.01) but females increased 3-hydroxyacyl-CoA dehydrogenase (BHAD) activity at the same incubation temperature (P=0.02). This data indicates that in vivo systemic factor(s) can alter skeletal muscle metabolism in vitro.