Parity-related changes in bovine follicle and oocyte populations,oocyte quality,and hormones to 90 days postpartum

Ultrasound-guided transvaginal follicular aspiration was used to obtain oocytes from Holstein cows to study follicular development and oocyte morphology during early lactation. A single aspiration was conducted on each of the 120 cows during wk 1 to 12 postpartum. On the day of aspiration, the number of follicles and their sizes were recorded. The collected oocytes were morphologically classified into four grades. Blood and follicular fluid samples were collected for hormone and metabolite assays. Greater serum nonesterified fatty acids concentrations for first- and second-parity cattle on d 7 implied a more negative energy balance status than for third-parity cattle. The numbers of follicles and oocytes retrieved were affected by linear days postpartum x parity interactions, with second-parity cattle having increases compared with decreases for third-parity cattle. Oocyte quality score was affected by the quadratic days postpartum x parity interaction. First- and second-parity cattle had greater oocyte quality scores from d 20 to 70 postpartum compared with third-parity cattle, but third-parity cattle had greater quality oocytes near the end of the 12-wk period. In contrast to cattle subjected to multiple aspirations, first- and second-parity cattle had higher estradiol and insulin-like growth factor I concentrations in follicular fluid associated with greater numbers of oocytes retrieved than third-parity cattle. This study demonstrated that conditions related to early lactation have a negative effect on oocyte quality and endocrine measures of dairy cattle and that animals of various parities may be differentially affected.