Effect of cow age on the in vitro developmental competence of oocytes obtained after FSH stimulation and coasting treatments.

The use of oocytes obtained from younger donors for IVF followed by embryo transfer represents an opportunity to accelerate genetic gain by reducing generation time. In this study, we investigated the relationship between donor age and the in vitro developmental competence of oocytes obtained from Holstein females (aged 5-18 months) after FSH stimulation and coasting. The follicle size patterns showed a significantly higher total number of small follicles (5-6 mm) from donors aged 5 to 10 months and a higher total number of medium-sized follicles (7-10 mm) in donors aged 6 to 7 months. Our analysis also revealed that the total number of follicles was significantly higher (P < 0.05) in donors aged 5 to 8 months and tended to be higher (P = 0.053) in nine-month-old donors. However, oocytes obtained from donors aged 5 to 10 months yielded fewer embryos reaching the morula and blastocyst stages. In summary, our results demonstrate that a higher number of oocytes can be obtained from younger animals but lower developmental competence negates this gain.