Investigation of Ovarian and Non-ovarian Associated Factors Related to Follicular Population and Oocyte Maturation of Chadian Cattle Breeds

A cow can give birth to an average of 6-7 calves in her entire reproductive period. The remaining oocytes could be used for the in vitro production of embryos. The present study was conducted to evaluate the effects of ovarian and non-ovarian factors on the follicular population and oocyte maturation of three Chadian cattle breeds (Arab, Kouri, and Toupouri). For this purpose, the ovaries of 166 cycled cows were collected at the Farcha slaughterhouse of Chad and placed individually in labeled conical tubes containing 0.9% NaCl and 0.5 mg/ml penicillin-streptomycin. After clearing the ovaries of tissue debris, they were weighed, and the follicles were counted. The diameter of each follicle was measured and classified into three categories. A total of 2734 oocytes were collected in 28 days with a minimum of 97 per day by the slicing method using a 10X stereoscope. They were then classified into four groups according to the structure of their cumulus oophorus. Immature oocytes (class 1 and 2 [1455]) were placed in different culture media consisting of Minimum Essential Medium (MEM) alone, MEM with 10% follicular fluid, and MEM with 50% follicular fluid for oocyte maturation. The results indicated that the mean follicular population and mean oocyte yield were 24.71 ± 0.88 and 11.65 ± 0.94, respectively. The mean oocyte index and the number of cultivable oocytes for in vitro embryo production (class 1 and 2) were 1.03 ± 0.23 and 1.65 ± 0.94, respectively. The number of follicles observed in the age group of 6-9 years was higher than in other age groups. Oocyte yield was significantly higher in cows with a body condition score of 4-5 compared to average and lean cows. Among the different culture media used for oocyte maturation, the medium consisting of MEM plus 10% follicular fluid recorded a higher maturation rate than the other culture media. Cows aged 6-9 years had a higher maturation rate than other age groups. In conclusion, the good follicle (follicle that produced oocyte) and appropriate oocyte performance were observed in cows with body condition score 3-5 and an age range of 6-9 years.