Calf production by bilateral embryo transfer or contralateral embryo transfer to previously inseminated cows

The objective of this experiment was to clarify the effects of embryo types and transfer methods on pregnancy rate, embryo survival rate, abortion rate and calves production following embryo transfer in beef cows. 29 cows each received nonsurgically three fresh embryos of in vivo fertilization (13 cows) or in vitro fertilization (16 cows) in the bilateral uterine horns (two embryos on side of the corpus luteum) on Days 7 to 9 post-estrus (bit-ET Group). 20 cows previously inseminated at the estrus each received nonsurgically two fresh embryos of in vivo fertilization (11 cows) or in vitro fertilization (9 cows) in the uterine horn contralateral to the corpus luteum on Days 7 to 9 post-estrus (AI+ET Group). Pregnancy and number of survival embryos were confirmed by real-time ultrasonic scanning at 20, 40, 60 and 80 days after transfer. Except for the Group received embryos of in vitro fertilization bilaterally in which pregnancy rate was lower and decreased gradually, high pregnancy rates, over 90%, were maintained during 20 to 80 days after transfer. Overall embryo survival rates (transferred and native embryo) during 40 to 80 days after transfer were significantly (p0.05 and p0.01) higher for embryo of in vivo fertilization than for embryo of in vitro fertilization, respectively, and these rates also tended to be higher in AI+ET Group than in bi-ET Group. Abortion rate after 90 days of gestation was lower in AI+ET Group than in bi-ET Group (5.6% vs 19.0%), but this difference was not significant. Transfer of embryo of in vivo fertilization resulted in significantly (p0.05) higher calf crop (155% based on recipients) and contralateral embryo transfer to previously inseminated cows also resulted in relatively higher calf crop (144%), compared with transfer of embryo of in vitro fertilization and bilateral embryo transfer, respectively (92% and 107%)