Age-related changes and circadian variations in peripheral levels of thyroid hormones in Murrah buffaloes

The aim of this study was to investigate the variations in plasma triiodothyronine (T₃) and thyroxine (T₄) with the advancement of age and to determine their circadian patterns in prepubertal and pubertal Murrah buffaloes. The variations in plasma T₃ and T₄ with the advancement of age were observed from day 1 to 24 months of age. Significant higher levels of T₃ and T₄ were observed after birth and a gradual decrease in their concentrations occurred until 15 days of age. The mean plasma T₃ and T₄ ranged between 1.26–3.79 and 60.7–166 ng/ml, respectively, during 1–30 days of age. During 1–24 months of age, the variations in plasma T₃ did not differ (p > 0.05) with the advancement of age, whereas significant (p < 0.0001) changes were observed in plasma T₄. The circadian patterns of T₃ and T₄ were evaluated in prepubertal Murrah buffaloes (n = 8) aged between 14 and 16 months. The mean plasma T₃ and T₄ ranged between 1.04–1.85 and 43.0–76.1 ng/ml, respectively. Significant (p > 0.0001) changes in the secretory pattern of T₃ were observed, whereas the secretory pattern of T₄ did not differ significantly (p > 0.05). In addition, the circadian patterns of T₃ and T₄ in pubertal buffaloes (n = 4) aged between 28 and 30 months were observed and compared to that of prepubertal group (n = 4). The prepubertal group showed significant (p < 0.001) higher plasma T₃ concentrations over 24 h than the pubertal group.