Effects of cadmium chloride exposure on in vitro maduration of bovine oocytes

The effects of cadmium chloride on in vitro maturation of bovine oocytes were studied. Ovaries were collected from slaughterhouse cows and oocytes recovered by the slicing technique. Oocytes were matured in TCM 199 for 24h at 38.5 degrees C in 5%CO2 in air, in presence of 0, 1, 5 and 10 ppm of cadmium chloride. At the end of culture oocytes were fixed for 24 h in etanol:acetic acid (3:1 v/v) at 4 degrees C. They were then stained in toto with 1.1% acetic orcein and the nuclear stage was observed under optic microscope. The ANOVA showed that cadmium caused a significant blockage of meiotic maturation (F = 150.996; P < 0.01) and induced oocyte degeneration (F = 89.92; P < 0.01) in concentration dependent manner. The percentage of oocytes that reached the Mll stage was greater in control group (P < 0.01) than in the cadmium-treated oocytes. A highly significant inverse correlation was established between the percentage of matured oocytes and the metal concentration in the medium (r = 0.818; P < 0.01), while the percentage of oocyte degeneration showed a highly significant direct correlation (r = 0.842; P < 0.01). Furthermore, chromosomal aberrations were observed, such as: picnosis, stekinesis and anaphasic bridges. Hence, a deleterious effect of cadmium chloride on in vitro matured oocytes by a blockage of meiotic maturation, induction of degeneration and chromosomal aberrations was established.