Monthly variations in thyroid hormones, thyrotropin, and testosterone in Dallagh rams

The aim of this study was to evaluate the monthly variations of triiodothyronine (T3), thyroxine (T4), T3 to T4 ratio, thyroid stimulating hormone (TSH), and testosterone in Dallagh rams during the breeding and non breeding seasons. Four healthy mature rams (3-4 years old) with an average body weight of 45±5 Kg were selected and kept in the same conditions. Blood samples were collected during June to November at three-week intervals. Serum was separated by centrifugation at 3000 rpm for 5 minutes. T3, T4, TSH and testosterone were measured by radioimmunoassay. During the experimental period, statistically significant changes occurred in the levels of serum T3 and TSH (P<0.05). The highest levels of T3 and TSH were observed in November and July, respectively; whereas, the lowest amount of T3 was observed in July. There were no significant differences in T4, T3 to T4 ratio and testosterone hormone during the experimental period (P>0.05). In conclusion, results showed that reproduction in Dallagh rams is not sensitive to day length and season. Therefore, they might be implemented in breeding and non-breeding seasons.