Seasonal variation in body mass index, cardinal physiological variables and serum thyroid hormones profiles in relation to susceptibility to thermal stress in goat kids

The influence of seasonal changes and susceptibility to thermal stress on body mass index (BMI), cardinal physiological variables (respiratory rate; RR, pulse rate; PR and rectal temperature; RT) and circulating thyroid hormone profiles (T3 and T4) was studied in Red Sokoto (n = 60) and Sahel (n = 60) goats during the cold-dry (CDS), hot-dry (HDS) and rainy (RAS) seasons. Using the RR, goats were grouped into cold stress susceptible (CSS) and cold stress tolerant (CST) phenotypes in the season with lower temperature humidity index (CDS) or heat stress susceptible (HSS) and heat stress tolerant (HST) phenotypes in the seasons with higher THI (HDS and RAS). Results revealed that the PR and RT were lower (P < 0.05), while circulating thyroid hormones and BMI were higher (P < 0.05) in Red Sokoto compared with Sahel goats. The RR, PR, RT and T3:T4 were significantly lower, while circulating T3 was higher during the CDS as compared with the HDS. Higher population of the goats were susceptible to cold and heat stress. Discriminant analysis showed higher misclassification of goats into HSS and HST phenotypes as compared with classification into CSS and CST phenotypes. The CSS phenotypes had significantly lower RT, but higher PR than the CST phenotypes. The HSS phenotypes had lower (P < 0.05) T3 than the HST phenotypes. Total variation in susceptibility to thermal stress was mainly explained by the RT, T3 and PR. In conclusion, unlike RT, PR and T3, BMI seems to have less influence on the susceptibility of kids to thermal stress. In addition, this study demonstrates the role of the thermogenic effect of T3 in the susceptibility and tolerance of kids to thermal stress.