Effect of climate on the seasonal endocrine profile of native and crossbred sheep under semi-arid conditions

Thirty-four 2-year-old ewes, of which 17 were native (Chokla) and 17 were A vivastra (Chokla 67.5%x32.5% Rambouillet) breeds of similar body weights, w ere selected. Both groups were maintained under the same management conditi ons with 8 hours daily grazing. In addition to grazing, each ewe received 3 00 g/day of a concentrate mixture comprising crude protein 20% and 70% tota l digestible nutrients. The ewes of both breeds were not mated during the s tudy. The daily environmental parameters were recorded throughout the year, consisting of four main seasons, namely rainy, winter, spring and summer. Blood samples were collected into heparinized tubes during the morning hour s for seasonal studies via indwelling jugular vein catheters to avoid stres s to the animals, but for the diurnal studies the sampling was done twice d aily at 07:00 and 17:00 continuously for three days in each season. Cortiso l, thyroxine (T-4) and triiodothyronine (T-3) were estimated in the samples . The T-4 and T-3 profiles were maximal in the summer, followed by the rain y season in both groups, with no significant differences. However, the cort isol in both the groups was maximal during the spring rather than the summe r. No significant differences were found in T-3 concentration between morni ng and afternoon in any season in the native ewes but these animals showed significantly higher levels of T-4 in the morning. The opposite was true fo r the crossbred animals with regard to both the T-3 and T-4 profiles. Signi ficantly more cortisol was found in the evening than in the morning in both genetic groups in all seasons.