Dt. Armstrong et al., GONADOTROPIN STIMULATION REGIMENS FOR FOLLICULAR ASPIRATION AND IN-VITRO EMBRYO PRODUCTION FROM CALF OOCYTES, Theriogenology, 42(7), 1994, pp. 1227-1236
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.