Influence of cadmium exposure on in vitro ovine gamete dysfunction

This study was conducted to determine the in vitro effects of three different cadmium concentrations (0, 2, and 20 microM CdCl(2)) on oocyte maturation, fertilisation, and acrosome integrity and sperm viability in sheep. Cumulus-oocyte complexes were recovered from ovaries of slaughtered sheep and sperm were collected by artificial vagina from adult rams. The oocyte maturation rate was significantly affected (P < 0.001) by Cd at both concentrations, with a metaphase II (MII) rate of 96.8, 63.8, and 32.0% for 0, 2, and 20 microM cadmium, respectively. In the second experiment, the presence of Cd significantly decreased (P < 0.01) the rate of oocytes resting in MII after 24-h postmaturation culture, compared with the control group (93.8 versus 29.0 and 19.8%, respectively, for 0, 2, and 20 microM Cd). Oocytes cultured with Cd 2 microM showed a higher activation rate (59.5%, P < 0.001) with one or two pronucleus than with 0 and 20 microM Cd (6.2 and 22.9%, respectively). During fertilisation the presence of fertilised oocytes was decreased in both culture systems with Cd compared with the control (76.1, 25.9, and 4.7% for 0, 2, and 20 microM Cd, respectively; P < 0.001) while polyspermy was increased in the 2 microM Cd group (23.5 for 2 microM versus 6.7 and 0%, respectively, for 0 and 20 microM groups). In both experiments Cd significantly increased (P < 0.001) the rates of oocyte degeneration. In the third experiment, Cd 20 microM significantly decreased (P < 0.01) the viability rate (35.6%) of spermatozoa compared with 2 microM (57.6%) and 0 microM (54.4%) while Cd 2 microM increased (P < 0.01) acrosome-reacted spermatozoa (45.2%) compared with 20 microM (32.5%) and control (31.9%). The results suggest that in vitro cadmium at the lowest dose tested affects the physiological function of both ovine gametes but at higher dose tested can compromise cell viability.