Preventing bloat in cattle when grazing clover

Grassland farmers are gradually coming back to white clover as a homegrown protein source and for its ability to fix up to 150kg N/ha each year, thus reducing dependence on artificial nitrogen. However, British farmers do need to manage this carefully as clover can cause bloat in cattle when grazed.

Bloat can occur when cows consume high clover swards, causing the rapid breakdown of protein in the rumen. Offering advice on prevention are grassland experts Dr Mary Evoy, Technical Director (Ireland), and Dr Michael Egan of Teagasc.

Causes of bloat in cattle

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

The ballooning rumen places pressure on the diaphragm, heart, and lungs, potentially causing sudden death if left untreated. For mild cases, bloat oil can be dosed to the animal as a treatment, while more severe cases might require veterinary assistance.

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

After a cow gets bloat, she is more susceptible to suffering from it again in the next two to three months, with a 60% chance of it reoccurring. This is because the rumen muscles stretch, leaving the animal unable to expel gases as efficiently.

Which fields have the highest bloat risk?

Leys with 40% or more clover are a high risk for animals, though incidences of bloat in cattle might also occur with less than that. Other factors that can cause bovine bloat are:

• Reseeded leys with high clover seeding rates.
• Releasing hungry animals onto grass-clover leys can induce gorging.
• Cattle are also at risk of bloat if they have not previously grazed grass-clover leys.
• A wet morning with heavy dew on leys can make grass highly digestible.
• Very lush grass with low pre-grazing herbage mass (under 1,400kg DM/ha) because fibre from grass is reduced.

How to prevent bovine bloat

Use bloat oil:

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

Prevention by grazing management:

• Use ‘breakfast breaks’ to remove the risk of cows gorging on clover. Use a strip wire for two to three hours after cows are turned into a fresh paddock. This stops them from preferentially selecting clover over grass. Cows can access the entire paddock after two to three hours.
• All animals should be turned out simultaneously to prevent the first cows milked from gorging on clover before the other cows arrive.
• When clover content is over 40%, consider feeding a source of fibre at milking. This could be 2-3kg a head of grass silage.
• Closely monitor cows when they graze in high-risk paddocks. The greatest threat is in the first two to three hours after turnout.
• Avoid grazing too tight (under 4cm) so that cows are not hungry when moving to the next paddock – this is to stop gorging.

The above measures can reduce bloat in cattle but there might still be a risk, so please maintain caution and always ask a vet if you are concerned about an animal’s wellbeing.

Trust the grassland experts

White clover can reduce artificial nitrogen inputs, saving money and bringing sustainability benefits to livestock production. Ask Germinal if you need advice on mixtures or establishment.