Intrafollicular transfer of fresh and vitrified immature bovine oocytes.

Embryo production by intrafollicular oocyte transfer (IFOT) represents an alternative for production of a large number of embryos without requiring any hormones and only basic laboratory handling. We aimed to (1) evaluate the efficiency of IFOT using immature oocytes (IFIOT) and (2) compare embryo development after IFIOT using fresh or vitrified immature oocytes. First, six IFIOTs were performed using immature oocytes obtained by ovum pickup. After insemination and uterine flush for embryo recovery, 21.3% of total transferred structures were recovered excluding the recipient's own oocyte or embryo, and of those, 26% (5.5% of transferred cumulus-oocyte complexes [COCs]) were morula or blastocyst. In the second study, we compared fresh and vitrified-warmed immature COCs. Four groups were used: (1) fresh immature COCs (Fresh-Vitro); (2) vitrified immature COCs (Vit-Vitro), with both groups 1 and 2 being matured, fertilized, and cultured in vitro; (3) fresh immature COCs submitted to IFIOT (Fresh-IFIOT); and (4) vitrified immature COCs submitted to IFIOT (Vit-IFIOT). Cumulus-oocyte complexes (n = 25) from Fresh-IFIOT or Vit-IFIOT groups were injected into dominant follicles (>10 mm) of synchronized heifers. After excluding one structure or blastocyst, the recovery rates per transferred oocyte were higher (P < 0.05) for Fresh-IFIOT (47.6%) than for Vit-IFIOT (12.0%). Blastocyst yield per initial oocyte was higher (P < 0.05) for Fresh-Vitro (42.1%) than for Fresh-IFIOT (12.9%). Vit-Vitro presented higher (P < 0.05) embryo development (6.3%), compared to Vit-IFIOT, which did not result in any extra embryo. Although IFOT did not improve developmental competence of vitrified oocytes, we achieved viable blastocysts and pregnancies produced after IFIOT of fresh bovine immature oocytes. Further work on this technique is warranted as an option both for research studies and for clinical bovine embryo production in the absence of laboratory facilities for IVF.