Pregnancy loss in cattle with emphasis on embryo transfer programs.

Pregnancy loss (PL) in cattle significantly impacts reproductive efficiency and economic viability of herds. Of particular interest, PL in in vitro embryo production (IVP) systems, represents a major challenge to the success of this technique. Establishment and maintenance of pregnancy is influenced by factors such as fertilization, maternal environment, and embryonic signaling issues. Data on dairy cattle have shown that embryo transfer (ET) may lead to greater initial pregnancy, but greater PL compared to artificial insemination (AI), and the impact of environmental conditions on reproductive outcomes seems to be manageable with proper heat stress mitigation strategies, for example. Data on beef cattle submitted to IVP and ET have shown that recipient cows had greater pregnancy per ET (P/ET) and lower PL compared to recipient heifers, with sex-sorted sperm yielding similar or even greater P/ET than conventional semen. Distinct synchronization protocols for recipients yield different reproductive outcomes, and recipient breed also affects P/ET and PL. Moreover, embryo recipients that express estrus after synchronization, as well as recipients in which better quality embryos are transferred, tend to have greater P/ET and lower PL. These findings highlight the importance of management strategies to improve fertility and reduce PL in embryo recipients.