Vol. 10, Issue 7 (2021)

Methods: Twenty-four GML roosters aged 36-weeks were divided into two groups (n=12). The heat stress group was exposed to 38 ℃ temperature and 40% Relative Humidity (RH) (Temperature-Humidity Index, THI=86) for 4 hours daily for a total period of 28 days in an environment-controlled chamber, and the control group was maintained at ambient conditions throughout the trial period. The mean ambient temperature and RH during this period were 28.7 ℃ and 63.4% respectively (mean THI being 78.29). Semen samples from both the groups were evaluated for semen volume, sperm concentration, sperm viability by MTT dye-reduction assay, and magnitude of free radical damage by lipid peroxidation assay at weekly intervals during the heat exposure.

Results: Semen volume and sperm concentration did not differ significantly between the two groups except for the first week of heat exposure wherein the sperm concentration in heat-stressed roosters was significantly reduced (P< 0.01). Percent live spermatozoa and sperm motility were significantly reduced in heat-stressed roosters (P< 0.01). The values of sperm viability and magnitude of free-radical damage to the sperm, as determined by MTT dye-reduction assay and lipid peroxidation assay, respectively varied significantly between the two groups (P< 0.01). The heat-stressed group showed poor viability and greater lipid peroxidation than the control, suggesting greater vulnerability of GML spermatozoa to heat stress. However, there was no significant difference in fertility and hatchability between the two groups.