Noninfectious Causes of Pregnancy Loss at the Late Embryonic/Early Fetal Stage in Dairy Cattle

SIMPLE SUMMARY: Pregnancy loss at any developmental stage affects the reproductive efficiency of cattle both at the individual and herd levels. In dairy cows, negative effects on milk production along with the increased antibiotic usage associated with pregnancy loss can have dramatic consequences on herd economy. Pregnancy loss during late embryonic and early fetal development can affect up to 20% of animals within a dairy cattle herd, so regular screening and pregnancy maintenance protocols are mandatory as it is important to identify animals at risk of losing their pregnancy after its diagnosis. In this review, we describe possible noninfectious causes of pregnancy loss during this late embryonic/early fetal stage. ABSTRACT: In cattle, initial pregnancy diagnosis takes place during the late embryonic/early fetal stage of gestation. From this point onward, pregnancy loss may occur in up to one fifth of pregnancies before the initial pregnancy diagnosis is confirmed. This means the early identification of risk factors is a key part of pregnancy diagnosis and herd management. The various factors responsible for pregnancy losses are classified into infectious and noninfectious. Among the noninfectious causes, several dam-related (circumstances of the individual pregnancy or milk production) and herd-related factors causing stress have been well established. In this review, we summarize the impacts of these noninfectious factors and predict associated risks of pregnancy loss.