Abstract:
Pregnancy losses include early embryonic death (EED) and later (postimplantation) abortion.
Abortions, particularly Equid herpesvirus (EHV-1) abortion epizootics, cause severe economic
and production losses. The long-term effects of EHV-1 and other abortions on subsequent
reproductive performance in broodmare populations, however, remain undefined. This study
described the relationships of EED and abortion with the following reproductive outcomes in
thoroughbred systems: breeding efficiency, month of last breeding, subsequent pregnancy
and live foal rates. A prospective cohort study in broodmare populations following EHV-1
epizootics on two South African farms was used to develop predictive models of the relative
influences and interactions of reproductive variables associated with EHV-1 and other
abortion causes on reproductive performance. EED predicted all the reproductive outcomes.
Abortion predicted increased effort and month of breeding to establish pregnancy, but not
becoming pregnant or foaling. Increasing age predicted decreased reproductive efficiency,
and pregnancy and foaling probabilities. Mare reproductive status predicted breeding
efficiency and the last month of breeding, but not establishing pregnancy. The last month
of breeding predicted efficiency, pregnancy and foaling. Interestingly, breeding in the first
month of the season was associated with an improved probability of pregnancy among
barren mares.
