Risk factors for reproductive disorders (metritis, endometritis, cystic ovaries, anovulation, low conception rate, embryonic mortality) in dairy cows

Reproductive disorders are defined here as clinically relevant reproductive events and disorders which the veterinary practitioner can detect and attempt to influence by altering the associated risk factors. The examples selected include metritis, endometritis, cystic ovarian disorder (COD), postpartum anovulation (PPA), low conception rate (LCR) and late embryonic mortality (LEM). Risk factors have traditionally been described at the herd- and cow-levels. Of more relevance to veterinary practitioners is the categorisation of these exposures as modifiable or non-modifiable. A modifiable risk factor describes a determinant that can be modified by the veterinary practitioner when the reproductive problem presents to prevent further cases in the current or often future breeding seasons. It was concluded from this review that clusters of common modifiable risk factors influence reproductive disorders in dairy cows. These are associated with nutrition (transition period negative energy balance - metritis, endometritis, COD, PPA, LCR, LEM; ketosis - metritis, endometritis, COD, PPA; milk fever - metritis, endometritis), reproduction (delayed ovulation - endometritis; AI practices - LCR, LEM; breeding season management - LCR, LEM), disease (uterine pathology - PPA, LCR, LEM; infectious diseases - LCR, LEM; lameness - COD, PPA, LCR; mastitis - COD, PPA, LCR, LEM) and general herd management factors (the cow's environment - endometritis, COD, LCR; genetic selection - metritis, COD, LCR, LEM; dry period duration - PPA, LCR; milking frequency - PPA, LCR).