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Cystic ovaries are generally regarded as spherical, ovarian structures at least 2.5 cm in diameter that persist for at least ten days in the absence of a corpus luteum.

Cows with cystic ovaries usually have abnormal oestrus cycles; persistent oestrus, shortened oestrus intervals or failure to cycle (anoestrus).  Behavioural signs range from lack of bulling to frequent, even bull-like behaviour. The tail head can become elevated, in some cases. Some degree of vaginal discharge is common.

The causes of ovarian cysts are poorly understood, and there is much debate regarding risk factors for ovarian cysts.  Nutritional risk factors for cysts include: –

  • High milk yield and negative energy balance
  • Uterine infections
  • Mycotoxins
  • A study has shown that the incidence of cysts for cows that were over-conditioned during the dry period was 29%
  • Selenium / vitamin E deficiency in the dry period
  • Risk of ovarian cysts also increases in heifers cows with elevated milk ketone concentrations

Current thinking is that the cyst producing hormonal imbalance is a direct result of stress. A recent survey of farms in the Netherlands demonstrated a strong correlation between early lactation production, body condition loss and cystic ovaries.

Dry cow feeding can help to reduce nutritional stress.  Prevention has to begin with condition scoring during late lactation.  During the last half of lactation, cows should be fed to achieve a score of 2.5 to 3.0 at dry off and maintained at this level through to calving. Adequate (but not excessive) body reserves will help to reduce negative energy balance in early lactation.  Close-up rations must be designed with the objective of minimizing the incidence of mik fever, ketosis, displaced abomasums and other disorders which occur after calving.

Several studies have demonstrated the beneficial effects of supplemental selenium along with vitamin A, vitamin E and beta carotene in maintaining immune competency and reducing the incidence of mastitis in fresh cows.  This in turn will reduce stress in early lactation and minimize the likelihood of cystic ovaries.

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