Infertility in Cows: Cystic Ovarian Disease

What is Cystic Ovarian Disease in cattle?

Cystic ovarian disease (COD) is a major problem associated with poor fertility in dairy cattle. Reportedly, from 6 to 19% of dairy cows develop cysts. It is possible, however, that the incidence of the disease is as high as 60%, as many heifers recover without intervention1, meaning they may go undetected. It is characterised by the presence of at least one enlarged anovulatory follicle on one or both ovaries which persists for more than 6 days. This disrupts the normal endocrine cycle of the cow and prevents her from cycling and going into heat.

This can have huge economic implications for the farmer as it increases the calving interval and dry period, and can lead to empty cows and increased veterinary expenses.2 In many cases, cows are culled as they are not profitable to keep.

What are the risk factors?

The likelihood of a cow developing cysts increases with parity. The more calves she has had, the more likely she is to develop COD.3 This is possibly skewed by selection bias. Farmers might keep a good milker in the herd for longer, even if she develops cysts.

Risk of cystic ovarian disease increases as a cow has more calves.
Risk of cystic ovarian disease increases as a cow has more calves.

If she has already had COD, then she is more likely to have it again. There is evidence of underlying genetic predisposition towards cysts and in environmental causes.4

Scientists and vets have linked nutritional imbalance to cystic ovarian disease. This is particularly common in cows with a negative energy balance or those that are eating very high protein feed.

Other risk factors include herd size, with a large herd leading to a higher incidence of the disease, poor housing conditions, and autumn calving. There is some debate around whether seasonality is significant, but a few studies have shown it to be relevant.

How do you diagnose Cystic Ovarian Disease?

Cows with ovarian cysts do not follow a normal oestrous cycle. As a result, behaviour and hormone tests, e.g. progesterone tests, will reflect this. Some cows will show masculinised behaviours such as increased bulling, pawing the ground, and bellowing. Other cows present as anestrous and might not show any clear behavioural signs. A vet will be able to diagnose ovarian cysts through use of an ultrasound or rectal palpitation and can then treat the cow.

How can you treat COD?

Some cows recover on their own, but many require hormonal treatments or dietary and nutritional management. Artificial hormones can stimulate the cow’s natural endocrine system and push her back into normal cycling. Sometimes vets use physical manipulation to rupture the cysts, but it can potentially damage ovarian function. As a result, this is not a common treatment option.

References

  1. Ijaz, A. et al., Br. Vet. J.143, 226–237 (1987).
  2. Laporte, H. et al., Livest. Prod. Sci. 38, 191–197 (1994).
  3. Nelson, S. et al., Acta Vet. Scand. 52, 60 (2010).
  4. Vanholder, T. et al., Reprod. Nutr. Dev. 46, 105–119 (2006).