Effect of follicular ablation and gonadotropin priming on the recovery and quality of oocytes in Boran cows

Genetic differences have been suggested as a possible cause for variation in responses to exogenous hormones. Here we evaluated the effect of follicle ablation, exogenous FSH and coasting time prior to ovum pick-up (OPU) on the number of follicles suitable for aspiration, oocyte quality, and cleavage rate in Ethiopian Boran cows. The experiment was carried out in three parts, I) Cows were synchronized using 500µg PGF2α given 11 days apart. Cows were then subjected to a biweekly ovum pickup session before ovulation (n=5) or starting Day 7 after ovulation (n=4) for three weeks. II) Cows were similarly synchronized and all visible follicles were ablated on the first days of overt estrus which were then further grouped into cows that received a divided dose of 350IU FSH (n=5) or 175IU FSH (n=5) over three days. In both groups OPU was carried out weekly starting 48h after the last FSH for six weeks. III) A similar protocol as in part II was carried out but coasting period was increased to 72hrs for cows that received 350IU FSH as divided dose (n=5) and 48hrs coasting period for single 350IU FSH dose (n=5). The covariates of follicles and oocyte were not affected (P>0.05) by corpus luteum presence at OPU. The mean number of medium (7.36±0.57) and large (8.28±0.96) follicles were significantly higher (P<0.05) in group that received divided 350IU FSH. Similarly, the mean number of Grade-1 (4.19±0.24) and Grade-2 (4.32±.27) COC, maturation rate (70.41%) and cleavage rate (47.5%) were significantly higher (P<0.05) in group that received 350IU FSH. COC quality was significantly (P<0.05) influenced by costing period. However, both maturation and cleavage rates were not affected by the coasting period. This study demonstrated that follicular ablation and treatment with FSH improves follicular population and oocyte recovery rate in Boran cows.