Effect of the relative locations of embryo and corpus luteum on embryo survival in cattle.

The objectives were to determine if early in gestation (less than day 30) an embryo in the ipsilateral horn increases the survival rate of an embryo in the contralateral horn and if later in gestation (greater than day 30) the presence of two embryos adversely affects the survival of both embryos in cattle. The experiment involved surgical embryo transfer. Sixty Holstein heifers were assigned to 4 groups: group 1) sham bilateral transfers, group 2) one embryo inserted ipsilateral to CL, group 3) one embryo inserted contralateral to CL, and group 4) one embryo inserted into each horn. Diagnosis of pregnancy and ovarian activity were recorded from day 7 or 8 (surgery) to day 110. Results indicated that the rate of embryo survival early in pregnancy (less than day 30) in heifers with the embryo inserted contralateral to the CL (33%, group 3) was increased (P = 0.05) when an embryo was also inserted into the ipsilateral horn (67%, group 4). The hypothesis that the ipsilateral embryo would have a protective effect on the contralateral embryo was, therefore, supported. This may have been due to the prevention of luteolysis by the ipsilateral embryo. However, when an embryo was present in each horn considerable loss occurred greater than day 30 resulting in a low survival rate by day 110 (27%). The hypothesis that the presence of two embryos would decrease the survival probability of both embryos later in gestation was, therefore, supported.