Potential health problems associated with clover

Bloat and fertility are common issues related to grazing clover. See our advice on minimising the impact in grazing livestock.

Back to: Managing clover


Bloat is a build-up of gas (carbon dioxide and methane) inside the animal, caused by the rapid breakdown of clover protein. Pressure exerted on the diaphragm, heart and lungs by the distended rumen causes distress and sometimes death.

Effective management can minimise or eliminate the risk of bloat in livestock grazing clover-dense swards:

  • Limit access when stock are first introduced to the field
  • Do not turn hungry stock out onto clover-rich pastures
  • Feed fibre, such as hay or straw, before turnout
  • Provide fibre (hay/straw) in the field
  • Take special care when the day is foggy or damp

There appears to be less risk of bloat when feeding red clover silage, but care must still be taken to provide a balanced ration. Discuss the risk of bloat with a qualified ruminant nutritionist and your vet.


Do not feed red clover – fresh or ensiled – to breeding ewes, or diseased white clover for six weeks before and after tupping. Red clover and stressed white clover contain high levels of phytoestrogens, which become more concentrated when ensiled. Phytoestrogens can cause ‘clover disease’ or ‘clover infertility’ in ewes.

Clover disease causes low lambing rates, prolapse, difficult lambing, uterus inflammation and bacterial infection. Clover infertility, which is caused by permanent damage to the reproductive tract, worsens with exposure to phytoestrogens. The structure of the cervix is damaged and sperm transport is affected, causing reduced conception rates.

Clover infertility has no visual signs: ewe cycling and ovaries appear normal. Accurate diagnosis is usually limited to abattoir feedback. Ewes fed high-estrogen clover may also suffer from temporary infertility, which can be reversed within a month of changing the diet. Vulva and mammary gland swelling will be visible in some breeds.

Effects are less severe in white clover, but high phytoestrogens can cause reduced ovulation and delayed oestrus. It is less common for breeding cows to graze red clover, but experiments have shown that silage made from this crop does not affect herd fertility.

Useful links

How to assess the clover content of your pastures

Read the Establishing and growing clover guide

If you would like to order a hard copy of the Establishing and growing clover guide, please contact publications@ahdb.org.uk or call 0247 799 0069.

The information in these web pages was sourced from Germinal, Grassland Development Centre (IBERS, University of Aberystwyth) and Charlie Morgan (GrassMaster Ltd).