GONADOTROPIN STIMULATION REGIMENS FOR FOLLICULAR ASPIRATION AND IN-VITRO EMBRYO PRODUCTION FROM CALF OOCYTES

Crossbred beef x dairy calves were randomly allocated at 3 wk of age t o different gonadotropin treatment regimens for stimulation of follicl e development and induction of oocyte maturation in vivo. Follicular r esponses were assessed laparoscopically, and oocytes were aspirated fo r assessment of maturational stale or for in vitro fertilization (IVF) and culture to determine developmental capacity. Follicle-stimulating Hormone (FSH), administered in a single subcutaneous injection togeth er with a low dosage of PMSG, was as effective as the same total dosag e of FSH administered in 6 injections over a 3-d period. Without accom panying PMSG, this dose of FSH was ineffective in stimulating follicle development. The mean number of preovulatory follicles (>5mm, with hy peremic appearance) doubled with each successive stimulation at 3-wk i ntervals, reaching 35 follicles pet calf at 9 wk of age. Oocyte yields ranged from 55 to 81% of follicles aspirated, and did not differ sign ificantly among age, FSH regimen and oocyte maturation stimulus. A com bination of LH + FSH was more effective in stimulating cumulus cell ex pansion than LH by itself (73 vs 22% of recovered oocyte-cumulus cell complex (OCC) respectively; P<0.05). Of 33 unselected immature oocytes (cumulus unexpanded) subjected to in vitro maturation (IVM) and IVF, 3O% developed to blastocysts during co-culture with bovine oviduct epi thelial cells, which was not significantly different from 25% of 36 oo cytes from adult ovaries which reached the blastocyst stage under simi lar conditions. The results indicate that follicle responses of calf o varies to FSH stimulation increase progressively from 3 to 9 wk of age , and that oocytes recovered laparoscopically from these follicles pro duce blastocysts in culture at rates similar to oocytes fi om adult ca ttle ovaries collected at slaughter. The approach offers promise for e mbryo production from donor calves of superior genetic merit for embry o transfer, thereby enhancing the late of genetic gain above that atta inable by conventional breeding or by embryo transfer in adult cattle.