While grazing is a natural activity for cattle, problems can occur when they graze on legumes such as alfalfa, sweet clover, red clover, alsike clover and white clover, which can cause bloat.
“While there can be problems with some legumes that have a tendency to cause bloat in cattle, there are also non-bloat legumes such as bird’s-foot trefoil, sainfoin and cicer milk vetch,” said Russel Horvey, a beef and forage specialist with Alberta Agriculture.
“The bloat caused by legumes is usually a frothy bloat. Understanding frothy bloat and how it is caused may help Alberta cattle producers understand bloat control on legume pastures.”
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Frothy bloat results from the quick degradation and fermentation of plant material in the gut and the rapid release of plant cell material. This material traps fermentation gases in a thick foam, which prevents the animal from burping up the gases. The accumulation of these trapped gases in the rumen can lead to the animal’s death.
“Forage maturity is the most significant contributing factor in pasture bloat,” Horvey said.
“The highest risk of bloat occurs when legumes are in the pre-bud or vegetative stage. As the plants mature, the risk of bloat declines. Again, this is because the fibre content in the plant increases as the plant matures and therefore breaks down more slowly in the rumen.”
To reduce the risk of bloat when grazing legumes:
- Never move hungry ruminants into legume pastures in the morning, which is when cattle graze the heaviest.
- Put animals out to pasture when the plants are dry. Water tends to speed up the rate of digestion, which contributes to the risk of bloat.
- Feed another source of dry roughage, one that contains long fibre material, before grazing a bloat-causing legume pasture.
- Maintain a uniform and regular intake of legume forages. Once cattle have started grazing, leave them on the pasture, even at night.
- Graze full bloom mature plants.
