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Animal Reproduction and Physiology
Asian-Australasian Journal of Animal Sciences 1992;5(1): 101-106.
https://doi.org/10.5713/ajas.1992.101    Published online March 1, 1992.
Thyroid hormones and testosterone in sheep Age related profiles of serum thyroxine, tri-iodothyronine and testosterone in Kaghani, Rambouillet and Kaghani x Rambouillet sheep
M. M. Ahmad, M. R. Mughal, A. Bari, M. I. Khan, M. Shahab
Secretory patterns of serum tri-iodothyronine, thyroxin and testosterone were analysed by specific radioimmunoassay in Kaghani (n = 42), Rambouilet (n = 42) and Kaghani 횞 Rambouillet (n = 42) male sheep to determine age and breed related changes. Animals were examined at 1-2 wk, 8, 10, 12, 20, 22 and 24 months of age (n = 6/age group). All animals were maintained under standard conditions of feeding and management. T3 and T4 concentrations were maximal (p<0.01) in 1-2 wk old lambs of all breeds studied (207.4 14.9 - 276.8 20.4 ng/dl and 5.76 0.3 - 7.23 0.9 關g/dl, respectively). For all the breeds, concentrations of T3 declined markedly (p<0.01) at 8 month of age and then varied in a narrow range (44.5 14.0 - 87.0 4.8 ng/dl) up to the age of 24 month. While, serum T4 concentrations decreased (p<0.01) to nadir (0.97 0.1 - 1.43 0.3 關g/dl) at 10 months of age in all the 3 breeds. Afterwards, T4 levels increased gradually and attained a small peak at 20 months before declining again at 22 and 24 months of age. Serum T3 and T4 concentrations were correlated significantly (p<0.05) and their ratio was constant at all ages in the different breeds. Age significantly (p<0.01) influenced the secretion of testosterone in the breeds examined but the breed differences were comparable. Mean serum concentrations of testosterone ere low from 1-2 wk to 10 months of age in the Kaghani, Rambouillet and Kaghani 횞 Rambouillet animals. Peak testosterone levels were noted in the 12 months old Kaghani (1.75 0.4 ng/ml), Rambouillet (1.30 0.2 ng/ml) and their F3 cross animals (1.16 0.08 ng/ml). Mean testosterone levels, thereafter, decreased at 20 months and then at 22 and 24 months remained variable but higher than observed at 1-2 wk -10 months of age. The findings of the present study indicate a significant influence of age but not of breed on the peripheral concentrations of thyroid hormones and testosterone. Serum concentrations of T3 and T4 were not related to testosterone levels. High thyroid secretory activity observed at prenatal phase of development may play an important role in preparing the lambs to extrauterine environments.
Keywords: T3; T4; Testosterone; Breed; Sheep
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