Endogenous and seasonal factors influencing circulating thyrotropin concentration in Red Sokoto and Sahel goats
Through regulating thyroid physiology, thyrotropin influences the activities of thyroid hormones, including thermogenesis and adaptation to ambient thermal challenges. This study aimed at evaluating the influences of some endogenous factors (breed, sex, age and body mass index; BMI) and season on circulating thyrotropin concentration in Red Sokoto and Sahel goats. A total of 120 goats were sampled, comprising Red Sokoto (n = 20) and Sahel (n = 20) goats in each season during the peak of the cold-dry (CDS), hot-dry (HDS) and rainy (RAS) seasons in a tropical Savannah climate. Results revealed that among Red Sokoto goats, bucks had significantly higher (P<0.05) circulating thyrotropin concentration than does during the HDS, while adults had significantly higher values than kids during the RAS. Significant (P<0.05) breed difference was only observed during the HDS, with the Red Sokoto goats having higher values among adult bucks and doelings but lower values than Sahel goats among buck-kids and adult does. Significant (P<0.05) seasonal variation was observed only in male Sahel goats with buck-kids having lower values during RAS as compared with CDS and HDS, while adult bucks had higher values during the RAS as compared with the HDS. A significant positive correlation (r = 0.29; P<0.001) was observed between thyrotropin concentration and BMI in the overall population. It was concluded that circulating thyrotropin concentration was higher in male and adult goats, and the effects of season and breed were sex and age-dependent. Moreover, the direct relationship between thyrotropin concentration and BMI may reflect the role of thyrotropin in the accumulation of body energy reserve in the savannah goats.