Effects of Metabolic Profile, Season and Stage of the Sexual Cycle on Follicular Dynamics, Quality and Oocyte Yield In Three Tropical Zebu Cattles - Abstract
Genetic and environmental factors have been reported to affect ovary characteristics. In the present study, we investigated the effects of metabolic profile on follicular population, oocyte quality and yield in three tropical cattle breeds. Blood and ovaries were collected from 195 zebu cattle (Gudali, Red and White Fulani) aged 3 to 15 years, with body condition score (BCS) of 2.93 ±0.65 (1 to 5) during slaughtering. The phases of sexual cycles were divided into proestrus, estrus, metestrus and diestrus. In each ovary, the follicle were counted and classified according to their diameter in small (<3 mm), medium (3-8 mm) and large (>8 mm) using an electronic caliper. Oocytes were collected by slicing technique and classified in class I, II, III and IV according to their cumulus investment and cytoplasmic distribution in four groups under a light microscope (400X). The metabolic or biochemical parameters were evaluate in the serum using automate and commercially available kits. Results show that from 390 ovaries, 6642 follicles were counted. The mean number of follicles per ovary was 18.45±0.58 and 15.74±0.48 respectively for right and left ovary. Small, medium and large follicles per cow represented 24.15±0.86; 9.30±0.39 and 0.61±0.05 respectively. The average number of follicles obtained per cow (34.06 ± 13.01) increased significantly with BCS (P<0.05). With the exception of total of class III oocytes, the overall number of follicles and oocytes were significant higher during rainy than dry season (P<0.05). Ovaries with corpus luteum presented fewer follicles than ovaries without corpus luteum. The highest number of large follicles was obtained during estrus phase of sexual cycle and the number of class I and II oocyte were obtain in proestrus. The mean oocyte yield per ovary was 8.34±0.28 and 7.02±0.24 respectively for right and left ovary. The quality of oocyte graded I, II, III and IV were 5.94 ±0.19, 3.29±0.16, 2.56 ±0.12 and 3.83±1.14 respectively. The average number of selected oocyte for in vitro embryo production represented 9.23±0.35 per cow and the oocyte index was 0.93. At the end of the research, we can easily see that, dry season negatively affect follicular population, oocyte yield and metabolic parameters. Estrus and proestrus are the best phases of the sexual cycle for the emergence of large follicles and good quality oocytes respectively.