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. / Master of Science / Heat stress (HS) presents a significant economic challenge to the livestock industry, particularly affecting the growth of skeletal muscle, which is vital for meat production. This problem is expected to worsen with climate change. In this study, we explored the potential of thyroid hormone (TH) supplementation to maintain metabolic flexibility in skeletal and cardiac muscles during HS. We exposed gilts to varying HS conditions and administered TH to determine its impact on metabolic processes in muscle tissues. Results showed that HS reduced metabolic flexibility, with TH supplementation having a beneficial effect on pyruvate oxidation in cardiac muscle under chronic HS conditions but no significant impact on skeletal muscle. Additionally, we compared the metabolic responses of male and female pigs under different environmental conditions and found that males tended to maintain better metabolic flexibility in vivo. In vitro experiments using muscle cell cultures confirmed that the systemic effects from HS pigs could alter muscle metabolism. These findings suggest that biological sex may impact some of the metabolic disruptions caused by HS, though further research is needed to fully understand the mechanisms involved.

This thesis examines in Swedish teacher education often neglected areas to increase the understanding for the essential differences between the two sexes and furthermore: how these differences affect us from an evolutionary and biological perspective. The study investigates previous research within the area - particularly evolution, neurology, hormones and genetics that affects our behavior. It also scrutinizes theories of social construction which primarily lodged the foundation for learning within the last century and served as explanation model for how human beings turn out in life. Research is analyzed regarding how music may be perceived differently and how they may affect stereotypical choices regarding instrument and other preferences. Also, the study evaluates research regarding how the Swedish school is designed to uphold gender equality in their goals and in their national curriculum. Finally, conclusions whether the Swedish school is providing enforcement regarding scientific regulations, which the law demands from it – in this case biological factors – are being looked at. The results show that biological differences between males and females may influence human behavior to a greater degree than earlier predictions, and that the Swedish school is mostly founded on a social constructionist point of view. These results indirectly question the Swedish National Agency for Education’s definition of equality, which paradoxical may lead to equity. Or, equality by outcome. Which do not take biological sex differences, or even individual differences into account.

This thesis examines in Swedish teacher education often neglected areas to increase the understanding for the essential differences between the two sexes and furthermore: how these differences affect us from an evolutionary and biological perspective. The study investigates previous research within the area - particularly evolution, neurology, hormones and genetics that affects our behavior. It also scrutinizes theories of social construction which primarily lodged the foundation for learning within the last century and served as explanation model for how human beings turn out in life. Research is analyzed regarding how music may be perceived differently and how they may affect stereotypical choices regarding instrument and other preferences. Also, the study evaluates research regarding how the Swedish school is designed to uphold gender equality in their goals and in their national curriculum. Finally, conclusions whether the Swedish school is providing enforcement regarding scientific regulations, which the law demands from it – in this case biological factors – are being looked at. The results show that biological differences between males and females may influence human behavior to a greater degree than earlier predictions, and that the Swedish school is mostly founded on a social constructionist point of view. These results indirectly question the Swedish National Agency for Education’s definition of equality, which paradoxical may lead to equity. Or, equality by outcome. Which do not take biological sex differences, or even individual differences into account.