Factors affecting pregnancy rate of embryo transfer in Bos indicus and Bos taurus/Bos indicus cows

The present study was conducted to determine the factors affecting pregnancy rate after embryo transfer (ET) in cows from the tropics. Zebu (n=105, Experiment I) andBos taurus/Bos indicus (n=110, Experiment II) potential recipients of embryos were synchronised with a norgestomet implant and received feed supplementation. In both experiments, recipients were divided in two groups: 1) subsequent spontaneous oestrus (SSO) and 2) synchronised oestrus (SO). At ET, recipients of Experiment I (n=50) and II (n=47) were transferred with a single frozen-thawed, in vitro fertilised F1 (Holstein/ Zebu) embryo. Pregnancy rate for Experiment I and II was 16% and 36.2%, respectively. In Experiment I, pregnancy rate was affected by day of transfer (day 7 or day 8, P < 0.05). In Experiment II, pregnancy rate was affected by oestrus type (SSO and SO), feed supplementation (with and without), and body condition score (low and high; P < 0.05).