The objective of this study was to determine the pregnancy rates and embryo mortality (EM) from embryos of different cattle breeds in a commercial program of in vitro production (IVP). We compare the number of pregnant recipients and EM from embryos of Angus, Nelore, Brangus, Holstein, Gyr and Girolando breeds.
Donors of the different breeds were subjected to ovum pick up (OPU), the cumulus-oocyte complexes (COC) were cultured for in vitro maturation (22h, 38°C, 5% CO2 in humidified air) and in vitro fertilized incubating 18h with frozen-thawed semen, prior centrifuged for capacitation. Embryos were cultured 7 days for development (22h, 38°C, 5% CO2 in humidified air) and classified according to IETS criteria. Only grade 1 embryos were considered for transfer. 19195 fresh morula and blastocyst stage embryos from 7 days post insemination (Angus=2576; Nelore=9715; Brangus=652; Holstein=647, Gyr=4231 and Girolando=1374) were transported to 12h in a portable incubator and transferred to crossbred heifers. Between days 28 to 32 after fertilization, the pregnancy status of recipients was determined by transrectal ultrasonography by visualization of the embryonic vesicle, totalizing 6503 pregnancies (Angus=848; Nelore=3569; Brangus=240; Holstein=147; Gyr=1256 and Girolando=443). Recipients diagnosed pregnant were reevaluated by ultrasound 35 to 40 days later to confirm embryo survival by finding the heartbeat and/or spontaneous movements. For statistical studies comparisons frequency and analysis by Chi-square were performed, considering a significance level p<0.05.
Pregnancy rate was 36.8% for Brangus (240), Nelore 36.7% (3569), Angus 32.9% (848), Girolando 32.2% (443), Gyr 29.7% (1256) and Holstein 22.7% (147). Significant differences (p<0.05) were observed between all breeds except Nelore vs. Brangus (p=0.97), Angus vs. Brangus (trend toward significance, p=0.06) and Gyr vs. Girolando (trend, p=0.07).
EM rate was 0.0% for Brangus, Gyr 4.9% (61), Nelore 5.1% (181), Girolando 6.3% (28), Angus 6.5% (55) and Holstein 12.2% (18). Significant differences (p<0.05) were observed between all breeds except Angus vs. Nelore, Nelore vs. Gyr, Nelore vs. Girolando and Gyr vs. Girolando. No Brangus embryonic losses were found.
In conclusion, the breed of the embryo significantly affects pregnancy rates in crossbred recipients, which affects production results in commercial OPU/PIV programs, further demonstrating marked improved performance of beef breeds embryos. Otherwise, EM in cattle is considered the main cause of reproductive failure and increased calving interval, meaning an even greater economic loss from embryos of high genetic PIV. Breed embryo significantly affects EM, proving a better performance of Bos indicus and their crossbreeds than pure Bos Taurus breeds.