The relationship of age and stage of gestation to the incidence of embryo death in dairy cattle.

Milk progesterone concentrations were measured thrice-weekly in approximately 200 autumn-calving cows of NIRD dairy herds in each of two successive years, about 100 being common to both years. From this, it was concluded that embryo death, later than the 14th day after artificial insemination occurred in about 10% of cows of each year. Most of the deaths occurred around the 35th day after AI, the time when the fetal membranes are becoming attached to the uterine wall. The incidence of embryo death around this time increases with age of cow.