Several studies have confirmed the thyroid hormones in volvement in the metabolic response of animals to certain nutritional, environmental and/or disease-related challenges, as well as in regulation of certain ovarian functions also in ruminants. Effects of hypothyroidism such as lengthening of the estrous cycle, have been reported in goats and sheep. The aim of this study was to determine the profiles of peripheral blood T3, T4 and TSH levels during estrus cycles in Markhoz goats. Five Markhoz does, aged 3 years, with an average weigh of 34.05±2.62 kg and with one kidding record were selected for determination of the serum total T3, T4 and TSH concentration during estrous cycle. Blood samples were collected every 10 days, from the beginning of the experiment. After 2nd standing heat, blood samples were obtained twice a week. Samples were allowed to clot at 37 ْC water bath for 60 min and then centrifuged at 1500 g for 15 min to separate serum. Sera stored at -57 ْC until assayed. Serum T3 and T4 were assayed using [125I] RIA KIT, and TSH was assayed using [125I] IRMA KIT. Average of estrous cycles lasted 20.93±1.54 days, which could be divided to luteal (14-15 days) and follicular (4-5days) phases. Average T3, T4 and TSH concentrations during follicular phase were 1.05±0.04, 5.36±0.18 μmol/ml and 0.16±0.02 μIU/ml, and during luteal phase were 0.93±0.04, 5.8±0.4 μmol/ml and 0.18±0.04 μIU/ml respectively. In comparison to control values for those parameters T3 had higher level at follicular phase, and returned to normal level at luteal phase, while TSH and T4 levels showed a reverse pattern of variations. So there is a correlation between the levels of thyroid hormones and normal ovarian function.
