Background: Ovaries remain inactive even after stabilization of metabolic status in some of postpartum dairy cows, but limited information is available about this chronic type of anestrus in bovine. Based on studies in human, loss of regular reproductive cycles could originate form ovarian failure due to diminished ovarian reserve.
Objectives: Therefore, the present study was conducted to test whether size of ovarian reserve contribute to the chronic type of anestrous condition in dairy cows.
Methods: To this end, cows with static ovaries up to 200 days postpartum were considered as cows with chronic type of anestrus (n = 24), and non-pregnant cows with cyclic ovaries were considered as the control (n = 24). The cows were subjected to blood sampling for evaluation of anti-Müllerian hormone (AMH; as a marker of ovarian reserve), and measurement of anogenital distance (AGD; as a marker of prenatal exposure to androgens). In addition, data associated with parity of cows, and their birth weight and date, and maternal parity were retrieved. The chronically anestrous cows were followed until drying-off, and cows in which the ovaries became reactivated were considered as recovered anestrous cows (n = 6), and cows that culled due to continuously inactive ovaries were considered as permanently anestrous cows (n = 18).
Results: AMH concentration was lower in permanently anestrous than cyclic cows (P < 0.05). Permanently anestrous cows were mostly from first and second parities (P < 0.05). The proportion of offspring born to nulliparous and primiparous dams was greater in permanently anestrous than cyclic cows (P < 0.05).
Conclusion: In conclusion, the present study showed that permanently anestrous cows had smaller ovarian reserve, and in turn, ovarian failure. A major proportion of cows with ovarian failure were from the first or second parities, indicating premature ovarian failure in this cows. Additionally, this study revealed that maternal nulliparity and primiparity may play a role in the pathogenesis of ovarian failure in cattle.