Ovulatory release and oviductal recovery after Intrafollicular Transfer of Immature Oocytes (IFIOT) in cattle.

Intrafollicular transfer of immature oocytes (IFIOT) is an emerging reproductive biotechnology that enables oocyte maturation, fertilization, and early embryonic development to occur in vivo. Despite its feasibility, IFIOT efficiency remains low, and the stages at which losses occur are not well defined. This study aimed to evaluate early post-ovulatory events after IFIOT by directly recovering structures from the oviduct, with particular emphasis on ovulatory release and early recovery dynamics under different oocyte loads. Immature cumulus-oocyte complexes (COCs) were recovered from slaughterhouse ovaries and transferred intrafollicularly into synchronized, non-lactating Nellore cows. Recipients presenting a single preovulatory follicle (≥10 mm) were randomly assigned to three experimental groups: a control group receiving medium only (CG; n = 16), a group receiving 5 COCs (G5; n = 15), and a group receiving 50 COCs (G50; n = 16). IFIOT was performed 54.5 ± 2.7 h after progesterone device removal, followed immediately by GnRH administration to induce ovulation and artificial insemination. Ovulation was confirmed by ultrasonography, and cows were slaughtered 64-66 h (2.5 days) after IFIOT. The ipsilateral oviduct was dissected and flushed to recover structures, and developing corpora lutea were examined macroscopically and histologically to detect retained COCs. Overall, 30.8% of the injected oocytes were recovered from the oviduct, with no differences in recovery rates between G5 and G50. Notably, COCs were identified within the cavities of developing corpora lutea 2.5 days after ovulation (G50: n = 16; G5: n = 2), indicating that a fraction of injected oocytes was not released during ovulation. These findings reveal incomplete ovulatory release as a previously underappreciated source of loss in IFIOT. These results provide new insight into early events following IFIOT and highlight ovulatory release as an important component to consider in efforts to improve the efficiency of this technique in cattle.