Sheep breed type effects on plasma thyrotropin, thyroxine and testosterone in growing ram lambs under hot climate

Received 9 September 2011, accepted 6 January 2012. Abstract The lack of knowledge about different physiological responses among indigenous sheep breeds raised in arid hot regions promoted the researcher to monitor a metabolic and a reproductive hormone in male lambs of two common breeds in Saudi Arabia. Forty eight growing male lambs (age 3-5 months) were grown in a private farm for fattening purpose. The animals were of two known breeds commonly raised in Saudi Arabia, namely Najdi and Noemi. Twenty four Najdi and 24 Noemi lambs were utilized in the study during hot months (June-August). Jugular blood samples were collected for eight consecutive weeks. Plasma was harvested and thyrotropin (TSH), thyroxine (T4) and testosterone (T) were determined. Significant (P<0.05) increases were found in TSH, T4 and T in Noemi (1.54 m IU/l, 11.91μg/dl and 6.25 ng/ml, respectively) compared to Najdi (1.39 m IU/l, 7.55 μg/dl and 3.38 ng/ml, respectively) lambs. The week to week changes in the levels of the three hormones were not statistically significant (P>0.05). The increases in the three hormones in Noemi males paralleled the concurrent increases in body growth rates (174 vs 139 g/hd/day for Noemi vs Najdi). In conclusion, within a species physiological differences are worth to be monitored for managerial purposes.