Seasonal variations in sperm acrosome reaction, osmotic tolerance and serum testosterone concentrations in rams

The study was conducted to evaluate the seasonal dynamics in the sperm acrosome reaction (AR), osmotic tolerance and serum testosterone concentration in rams. Blood and semen samples were collected from six mature rams during the winter, spring, summer and autumn seasons. The AR in sperm samples was induced by using lysophosphatidylcholine (LPC) and calcium ionophore (CI). The AR was monitored at various incubation times (15, 30, 60, 120 and 180 min) post-induction. To determine the osmotic tolerance through hypo-osmotic swelling test (HOST) the sperm were exposed to different osmotic conditions (50, 100, 290, 500 and 1000 mOsm/L). The serum testosterone concentration was assessed using a solid phase enzyme-linked immunosorbent assay (ELISA). The proportion of acrosome reacted sperm was greater (P <  0.05) during the winter season in the LPC and control groups, whereas, it was greater (P <  0.05) in two different seasons (winter and summer) at all incubation time points (15-180 min) in the CI group. The live HOST +ve, total HOST +ve and total live sperm were least (P <  0.05) during the winter season. The greatest membrane integrity (P <  0.05) was in the autumn season. The peak (P <  0.05) serum testosterone concentration was during the summer season. In conclusion, the osmotic tolerance and sensitivity of ram sperm to undergo the AR in response to LPC and CI vary with season. The increased testosterone concentration in the summer season might be the reason for a greater membrane integrity during the subsequent autumn season in Kivircik ram sperm.