EFFECT OF FREQUENCY OF FOLLICLE ASPIRATION ON OOCYTE YIELD AND SUBSEQUENT SUPEROVULATORY RESPONSE IN CATTLE

The effect of frequency of transvaginal follicular aspiration on oocyt e yield and subsequent superovulatory response was studied in 2 experi ments. In Experiment 1, 32 primiparous Hereford x Friesian cows were a ssigned to 4 treatments (n = 8 per treatment). Oocyte recovery was car ried out once a week for 12, 8, 4 or 0 (control) wk. Embryo recovery f or all animals was 7 wk after the completion of the aspiration schedul es. In Experiment 2, the effects of oocyte recovery once or twice a we ek (n = 8 per treatment; control n = 18) for 12 wk and response to sup erovulation 4 wk after the last aspiration were compared using nullipa rous purebred Simmental heifers. Increasing the period of once weekly aspirations from 4 to 12 wk (Experiment 1) did not affect the number o f follicles observed per session (mean +/- SEM; 10.0 +/- 0.82) or aspi rated (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 f or 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 p rocedures, estrus or estrous activity was observed in 7/8, 8/8, 7/8 an d 6/8 of the animals aspirated over 12, 8, 4 or 0 wk, respectively. Su bsequent superovulatory responses and in vivo embryo recoveries were s imilar for all aspiration treatments and for control animals. Changing the frequency of oocyte recovery from once to twice weekly (Experimen t 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), oo cytes recovered (1.7 +/- 0.27 vs 1.9 +/- 2.0) per session or the oocyt e recovery rate (29.4 +/- 2.4 vs 30.4 +/- 2.4 %); nor was there any ef fect of frequency of aspiration on subsequent superovulatory response and embryo recovery. In conclusion, increasing the period of aspiratio n 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 nu mber of oocytes recovered per donor per session. Subsequent estrous cy clicity and responses to superovulation were unaffected by the periods or frequencies of oocyte recovery examined here. (C) 1997 by Elsevier Science Inc.