188 Effects of season and breed on in vitro beef embryo production and recipient pregnancy rate

Embryo transfer (ET) is a widely used reproductive technique in cattle herds, with ~85% of the embryos used being produced in vitro (IVP). However, several aspects must be considered to successfully use this technique, such as nutritional and reproductive management, as well as oocyte quality. The aim of this study was to evaluate the influence of donor breed (Nellore vs Senepol) and season (dry (DS) vs rainy (RS)) at the moment of follicular aspiration (OPU) on number of viable oocytes (VO) and embryos (VE) produced, as well as pregnancies per embryo transfer (P/ET) of recipients. Data from 198 Senepol and 170 Nellore oocytes donors collected during 2021, in a commercial IVP laboratory, localised in Minas Gerais State, Brazil, were analysed. Follicular aspiration and ET data were collected in DS and RS, and response variables for VO were collected, blastocyst production at Day 7 and recipient P/ET. Pregnancy diagnosis of recipients was performed 30 days after oestrus. During this evaluation, embryo viability was observed by the presence of a heartbeat. The number of VO and VE produced were assessed with analysis of variance including in the model the effects of oocytes, donor breed, and season at the OPU and the interaction. Recipient P/ET was analysed by logistic regression including in the model the effects of oocytes, donor breed, and season at the ET and the interaction, both in Minitab software. Statistical significance was defined as P ≤ 0.05. A total of 608 OPUs were performed. During RS 197 OPUs were performed on Nellore donors resulting in 26.2 ± 1.11 VO; 31.9% of embryo production rate (EPR); and 8.2 ± 0.49 VE, and during the DS, 134 OPUs were performed leading to 18.8 ± 1.01 VO; 37.8% EPR; and 7.4 ± 0.51 VE. For Senepol donors during the RS, 173 OPUs were performed resulting in 28.6 ± 1.28 VO; 26.2% EPR; and 7.3 ± 0.50 VE, and during the DS 104 OPUs were realised in Senepol cows, leading to 27.5 ± 1.61 VO; 31.4% EPR; and 8.4 ± 0.72 VE. An effect of the interaction of season at OPU and donor breed was observed on number of VO collected and EPR (P < 0.01); however, no effect of the interaction was detected on number of VE (P > 0.05). During the DS a higher number of VO in Senepol donors was collected compared with Nellore donors. Nellore donors presented a higher EPR than Senepol in DS, resulting in the same number of VE. Considering P/ET, in the RS, 554 Nellore and 544 Senepol embryos were transferred, resulting in 37.9% and 42.8% P/ET, respectively, and in the DS 321 Nellore and 223 Senepol embryos were transferred, resulting in 35.2% and 29.e% P/TE, respectively. An effect (P < 0.01) of interaction between oocyte donor breed and season at ET was detected on P/ET. Higher P/ET was detected for embryos from Nellore oocytes that were transferred during the DS when compared with pregnancy rates for Senepol. In conclusion, during the DS fewer VO from Nellore donors were collected; however, the EPR was higher, resulting in a similar number of VE for both donors’ breed. Embryos produced from Senepol oocytes result in lower P/ET during the DS.

The authors acknowledge CAPES, CnPQ, and FAPEMIG.