Transfer of immature oocytes to a preovulatory follicle: an alternative to in vitro maturation in the mare?
In the mare, success rates for the in vitro maturation of oocytes are low. Accordingly, we attempted to determine if immature oocytes could be matured in vivo by injecting them into a preovulatory follicle. Groups of 3-9 oocytes collected from donor mares were transferred under ultrasound control into the preovulatory follicle of a recipient mare that was treated with crude equine pituitary gonadotrophin (CEG) to induce ovulation. Just before ovulation (34 h post treatment) the preovulatory follicle of the recipient mare was punctured to collect both the transferred and the indigenous oocytes to analyse the stages of nuclear maturation. The transfer technique did not impair significantly the final maturation of the recipient preovulatory follicle. The indigenous oocytes within the recipient follicles were recognisable by their larger expanded cumulus of yellow colouration due to high hyaluronic acid content; 7/12 of these oocytes were mature (metaphase II). Around half (42/86; 49%) of the oocytes transferred to preovulatory follicles were recovered subsequently. Most of them showed cumulus expansion (41/42, 6 of which were rich in hyaluronic acid), 13 (32%) were mature, 15 (36%) were immature and 13 (32%) were degenerate. When the indigenous oocyte of the recipient mare was mature, 38% of the transferred oocytes were mature, this rate being no different from the in vitro maturation rate of 46%. This study showed that in vivo maturation of immature oocytes by transfer into a preovulatory follicle in a recipient mare is possible. The maturation rate is not different from the in vitro maturation rate. The technique allows the generation of mature oocytes that have an expanded cumulus rich in hyaluronic acid, similar to the situation in preovulatory oocytes. This result has not been obtained in vitro previously.
Goudet
G
G
INRA-Haras Nationaux, P.R.M.D. Unité de Reproduction Equine, Nouzilly, France.
Bézard
J
J
Duchamp
G
G
Palmer
E
E
D000818:Animals; D004958:Estradiol / Q000032:analysis; D005260:Female; D015571:Follicular Fluid / Q000737:chemistry*; D006736:Horses / Q000502:physiology*; D007315:Insemination, Artificial / Q000662:veterinary; D018587:Oocyte Donation / Q000662:veterinary; D009865:Oocytes / Q000166:cytology / Q000502:physiology / Q000637:transplantation*; D006080:Ovarian Follicle / Q000166:cytology / Q000502:physiology* / Q000637:transplantation; D011374:Progesterone / Q000032:analysis; D011677:Punctures / Q000662:veterinary; D013739:Testosterone / Q000032:analysis
D013739:Testosterone; D011374:Progesterone; D004958:Estradiol