113 Volume of medium used for intrafolicular transfer of immature oocytes impacts its results

Several factors determine the efficiency of intrafollicular oocyte transfer (IFIOT), including the volume of medium used to inject cumulus–oocyte complexes (COC) into the dominant follicle. This study aimed to evaluate whether the volume of medium and the injection quality affects follicle size and oocyte recovery postinjection. Thirty Nellore heifers were synchronized as described by Faria et al. (2021 Reprod Fertil Dev. 33, 372–380) and 30 h after progesterone device removal (D9.5) the dominant follicle of all animals was measured by ultrasonography. The animals were then distributed into 2 groups: (1) IFIOT-60 (n = 18): injection of up to 60 µL of phosphate-buffered saline (PBS) + 25–30 COCs (control group); and (2) IFIOT-20 (n = 18): injection of 20 µL of PBS + 25–30 COCs. The quality of injection was classified as grade 1: needle positioning in the centre of the follicle, with the visualisation of all structures being deposited at a constant pace, without perception of follicle regression after needle removal; grade 2: injection in the periphery of the follicle, with the visualisation of structures being deposited too fast, causing a vortex effect, or very slowly, almost imperceptible after injection, or more than one perforation in the same follicle, with sometimes immediately perception of follicle regression after the procedure. After 22 h of IFIOT, all follicles were measured and COCs were recovered by ovum pickup. The results were analysed by chi-squared and Proc GLIMMIX (SAS Institute). In general, the injection caused a reduction on the diameter and volume of follicle (P < 0.05) and no difference was observed among groups (P > 0.05), regardless of the quality of the injection. However, the volume used for the injection affected (P < 0.05) the percentage of recovered COCs, being higher in group IFIOT-60 (69.79%) than in IFIOT-20 (58.81%). When only grade 1 injection was considered, the recovery rate was similar (P > 0.05) between groups (P > 0.05; 67.58% and 68.44%). Unexpectedly, when grade 2 injections were analysed a difference (P < 0.05) in recovery rate was observed between IFIOT-60 (n = 2/14; 83.33%^a) and IFIOT-20 (n = 6/15; 44.03%^b; superscript letters indicate difference between treatments). The results suggest that the amount of medium used affects the recovery rate, but this effect depends on the quality of the injection and not on the reduction of the follicle. Then, are other aspects of quality injection that seem to be associated to the efficiency. From the moment it stops using up to a certain volume injected and starts using a specific volume, the processes become standardized without changing the results obtained.

Financial support for this study was provided by FAPDF, Embrapa, and CAPES.