Advice for preventing bloat in cattle when grazing grass with clover

Tuesday 11.06.2024 , News

White clover can help reduce artificial nitrogen use by fixing up to 150kg N/ha annually and is coming back to prominence on Irish livestock farms. However, clover can cause bloat in cattle when grazed and needs to be managed to prevent such an issue.

Bloat can occur when cows consume high clover swards, causing the rapid breakdown of protein in the rumen. Below, Dr Michael Egan of Teasgasc and Germinal Technical Director Dr Mary McEvoy give advice on prevention.

Causes of bovine bloat

Ruminant animals produce large volumes of gas during digestion. This gas is usually belched or passes through the gastrointestinal tract. As clover increases the rate of breakdown in the rumen, the build-up of gas is greater and exceeds the animal’s ability to expel the gas, thus causing bloat.

The ballooning rumen places pressure on the diaphragm, heart, and lungs, which can cause sudden death if not treated. In mild cases, bloat oil can be dosed to the animal as a treatment. However, in more severe cases, veterinary assistance may be required.

The most common sign of bloat is a distended left abdomen, but affected animals will also show signs of discomfort, including respiratory distress.

When a cow gets bloat, she is more susceptible to suffering from it again within the next two to three months (there is a 60% chance of it reoccurring). This is because the rumen muscles stretch, and they are not able to expel gases as efficiently.

What makes a field high risk for bloat?

Typically, a sward with a clover content of more than 40% represents a high risk for animals. However, incidences of bloat in cattle may also occur when the clover content is lower than this.

There are other factors that can lead to bovine bloat, including:

  • Having hungry animals prior to allocating grass-clover swards – this induces gorging.
  • Animals are also in danger of getting bloat if they have not had access to grass-clover swards previously.
  • A wet morning with heavy dew on the pasture because this makes the grass highly digestible.
  • Very lush grass with low pre-grazing herbage mass (<1,400kg/DM/ha) because fibre from grass is reduced.
  • Reseeded swards containing high clover seeding rates.

How to prevent bloat in cattle

Use bloat oil:

  • Adding bloat oil to drinking water can help reduce the risk of bloat. It should be introduced 24 hours before stock moves to the risk paddock. In periods of wet weather, animals may drink less water from the trough, so it may not eliminate the risk.

Grazing management for prevention:

  • Use ‘breakfast breaks’ to remove the risk of cows gorging on clover. This involves using a strip wire for two to three hours after cows are turned into a fresh paddock. This prevents cows from preferentially selecting clover over grass, thus reducing the risk. After two to three hours, animals can be given access to the whole paddock.
  • All animals should be turned out to the paddock at the same time to prevent the first cows milked from gorging on clover before the other cows arrive in the paddock.
  • If clover content is particularly high (>40%), consider feeding a source of fibre at milking. For example, 2-3kg a head of grass silage.
  • Avoid grazing too tight (<4cm) so that cows are not hungry when moving to the next paddock. This will prevent gorging.
  • Closely monitor cows when they are grazing high-risk paddocks. The first two to three hours after turnout pose the greatest threat.

While all the above will reduce bloat in cattle, even with preventative measures in place, there still may be a risk, so farmers must remain vigilant.

Interested in establishing grass-clover swards?

Ask Germinal, the grass and forage experts.