Effect of age and season on the thyroid hormone activity of Mizoram strain female mithun (Bos frontalis)

AIM: The aim of the present study was to generate baseline data on the normal values of the thyroidhormone (TH) activity as well as their correlation with age and season. MATERIALS AND METHODS: Blood samples (10 ml) were collected from jugular vein of 30 female mithun’s of three different age groups viz. Calves (6 months to 1 year), heifer (1-3 years) and adult (above 3 years) during the three season’s viz. Monsoon, winter and spring of a year. The serum was analyzed for thyroid stimulating hormone (TSH), triiodothyronine (T(3)), and thyroxine (T(4)) activity. RESULT: The result showed a significantly (p<0.05) a higher T(3) level in heifers followed by adults and calves and higher T(4) level in adults followed by heifers and calves in all the seasons. The TSH level was higher in heifers in all the seasons. The winter season recorded higher level of T(3), T(4), and TSH as compared to the other seasons of a year. CONCLUSION: The TSH and T(3) level were the highest for aheifer, whereas T(4) level was the highest for adults inall the season. Furthermore, the higher level of TH was observed in winter season. The increased level of the TH during the winter season signifies their calorigenic effect. Similarly in heifers, the increased T(3) concentrations show its importance in reproductive physiology and its association with ovarian activity. This indicates that age and season have aprofound effect on TH activity of Mizoram strain female mithun.