Factors affecting embryo survival and strategies to reduce embryonic mortality in cattle

Embryonic mortality in cattle is the death of the conceptus before Day 42 of pregnancy. Estimates of embryonic mortality varied greatly, ranging from 10 to 40% in first-service cattle to 65% in repeat-breeder cows. This paper reviews endogenous causes of embryonic mortality, including chromosomal abnormalities, inadequate corpus luteum function and the influence of follicular development on fertility. External causes of embryonic mortality, including heat stress and nutrition, are also reviewed; these factors act by modifying the follicular environment (thereby affecting oocyte quality) or by creating a hostile uterine environment. Strategies to reduce embryonic mortality, including good management practices and supplementation with progesterone or interferon-tau, are discussed. From a practical perspective, improved knowledge of the causes of embryonic mortality and regulation of follicular growth and corpus luteum function should result in the development of improved, cost-effective hormonal regimes that effectively synchronize estrus and ovulation and reduce embryonic mortality, thereby benefiting the cattle industry. Key words: Cattle, reproduction, fertility, embryo development, embryo mortality