Effect of frequency of follicle aspiration on oocyte yield and ubsequent superovulatory response in cattle

The effect of frequency of transvaginal follicular aspiration on oocyte yield and subsequent superovulatory response was studied in 2 experiments. In Experiment 1, 32 primiparous Hereford x Friesian cows were assigned to 4 treatments (n = 8 per treatment). Oocyte recovery was carried out once a week for 12, 8, 4 or 0 (control) wk. Embryo recovery for all animals was 7 wk after the completion of the aspiration schedules. In Experiment 2, the effects of oocyte recovery once or twice a week (n = 8 per treatment; control n = 18) for 12 wk and response to superovulation 4 wk after the last aspiration were compared using nulliparous purebred Siremental heifers. Increasing the period of once weekly aspirations from 4 to 12 wk (Experiment 1) did not affect the number of follicles observed per session (mean ± SEM, 10.0 ± 0.82) or aspirated (7.8 ± 0.71), but the recovery rate of oocytes from follicles aspirated was greater for donors aspirated for either 4 or 8 wk than for 12 wk (32.3 ± 3.73 vs 28.4 ± 2.61 vs 20.1 ± 2.13 %; P<0.05). Following the last aspiration and prior to commencing superovulatory procedures, estrus or estrous activity was observed in 7/8, 8/8, 7/8 and 6/8 of the animals aspirated over 12, 8, 4 or 0 wk, respectively. Subsequent superovulatory responses and in vivo embryo recoveries were similar for all aspiration treatments and for control animals. Changing the frequency of oocyte recovery from once to twice weekly (Experiment 2) did not affect the numbers of follicles observed (9.1 ± 0.63 vs 8.3 ± 0.85), follicles aspirated (5.9 ± 0.56 vs 6.2 ± 0.69), oocytes recovered (1.7 ± 0.27 vs 1.9 ± 2.0) per session or the oocyte recovery rate (29.4 ± 2.4 vs 30.4 ± 2.4 %); nor was there any effect of frequency of aspiration on subsequent superovulatory response and embryo recovery. In conclusion, increasing the period of aspiration from 4 to 12 wk and the frequency from once to twice a week over 12 wk did not reduce the number of follicles observed or aspirated, or number of oocytes recovered per donor per session. Subsequent estrous cyclicity and responses to superovulation were unaffected by the periods or frequencies of oocyte recovery examined here.