Effects of heavy metals and pesticides on buffalo (Bubalus bubalis) spermatozoa functions in vitro

Industrial toxic metals, pollutants and bio-accumulative pesticides interfere with the male reproductive functions in farm animals. Frozen-thawed semen samples were incubated with heavy metals (cadmium and lead) and pesticides (chlorpyrifos and endosulfan) of different concentrations (0, 0.005, 0.05, 0.02, 0.1, 0.5, 1.0, 2.0 and 4.0 μg/ml) for 1 h, and various spermatozoa functional parameters and in vitro fertilization rates were assessed. Any significant effect was assessed by comparing the 1 h data between the control and treatment groups. Progressive forward motility was significantly (p < 0.05) reduced in spermatozoa exposed to lower concentrations (0.05-0.5 μg/ml) of toxic substances. The straight-line velocity (μm/s) and the average path velocity (μm/s) were significantly (p < 0.05) reduced in spermatozoa exposed to 1.0 and 0.5 μg/ml of cadmium (11.6 ± 1.9 and 16.3 ± 1.9) and chlorpyrifos (10.4 ± 1.5 and 17.1 ± 1.3), respectively, when compared to control (20.4 ± 1.4 and 28.1 ± 1.7). The acrosomal integrity was also significantly (p < 0.05) reduced at 0.05 μg/ml of chlorpyrifos (33.3 ± 1.9), 1.0 μg/ml of cadmium (36.8 ± 3.7), 1.0 μg/ml of lead (39.4 ± 2.8) and 0.5 μg/ml of endosulfan (38.3 ± 3.2), respectively. The spermatozoa chromatin decondensation was significantly (p < 0.05) affected at higher concentrations (>0.5 μg/ml) of these chemicals. The mitochondrial membrane potential (%) was significantly (p < 0.05) reduced at 0.05 μg/ml of cadmium (3.2 ± 0.2) and chlorpyrifos (4.3 ± 0.4), 0.1 μg/ml of lead (3.8 ± 0.3) and 0.5 μg/ml of endosulfan (3.2 ± 0.3) when compared to control (6.7 ± 1.0). The in vitro fertilization capabilities (cleavage percentage) of spermatozoa were significantly reduced at 1.0 μg/ml of cadmium (28.3 ± 2.4) and 2.0 μg/ml of lead (31.1 ± 2.7), chlorpyrifos (29.4 ± 2.2) and endosulfan (32.6 ± 2.5) when compared to control (59.4 ± 4.4). This study suggested that the mitochondrial membrane potential was primarily affected even with lowest doses of toxic chemicals. Cadmium when compared to lead and chlorpyrifos when compared to endosulfan were found to be more toxic to the spermatozoa.