Egg transfer in the cow: factors affecting pregnancy and twinning rates following bilateral transfers.

A total of 112 heifers was used in an egg transfer study to examine some of the factors affecting egg survival and twinning rates following bilateral transfers. Seventy-two recipient heifers were involved and pregnancy rates of 82.0 percent, 66.7 percent and 61.5 percent were recorded for recipients in oestrus on the same day as (Day 0), 1 day before (Day + 1) and 1 day after (Day minus 1) the donor respectively. Short-term (10-day) intravaginal progesterone, or intramuscular prostaglandin treatments for synchronization of oestrus in recipient animals did not depress pregnancy rate following egg transfer. One egg was transferred to each uterine horn and twinning rates of 55.6 percent, 44.4 percent and 20.0 percent were recorded for transfers on Days 0, + 1 and minus 1, respectively. Of the recipients becoming pregnant following transfers on Day 0, 74.1 percent had twins. Embryo survival was higher (69.2 percent) in the uterine horn adjacent to the ovary containing the CL than in the opposite horn (30.8 percent). The storage period in vitro in TC199 (37 plus or minus 1 degrees C) aftected subsequent egg survival rates following transfer, with fewer eggs surviving the longer storage periods. The pH of the medium used for egg collection and storage did not affect the pregnancy rate between pH values of 7.0 to 8.6. Day of transfer (Days 3 to 7) did not seem to affect the pregnancy rate. The high pregnancy and twinning rates already reported following closely synchronized transfers were confirmed.