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Bloat is the accumulation of excess gas in the rumen. It can develop in less than one hour after introduction to a high-risk paddock, but more often it develops after one day.

The gas can either be:

  • free – accumulating because the rumen is flaccid and not performing its usual eructation function
  • frothy – due to chemicals increasing the surface tension of the rumen liquid.

Conditions when bloat is likely to occur

  • Wilted green forage and some plants can contain prussic acid which leads to rumen paralysis and free gas bloat.
  • Lush rapidly growing legume pastures can cause frothy bloat. More likely to occur with legume pasture in rapidly growing vegetative stage and in highly digestible pasture with a low dry matter percentage. The highest risk pasture is lucerne, followed by white clover, then subterranean clover.
  • Intensive ration feeding with a low fibre component (where greater than 80% of the ration is grain). This type of ration feeding occurs mainly in feedlots or during drought feeding.

Identification and diagnosis

Clinical signs for bloat in a group of animals grazing high risk pastures or on grain include:

  • sudden death
  • distension in the left upper flank if still alive or if others in mob are showing mild signs
  • the condition is painful and affected cattle will be agitated and may vocalise or rub their sides against objects such as tree stumps.


An integrated approach to prevent bloat should consider the following:

  • assessing, or gaining professional advice to ascertain the bloat risk of your pastures
  • identifying pastures as high risk for bloat if they have a high proportion of legumes with lush and vegetative growth
  • using grazing management to avoid grazing these high-risk pastures
  • slowing the rate of rotational grazing so cattle graze more mature pastures
  • daily application of bloat oil on pasture may be cost-effective against frothy bloat in some situations. Bloat oil in water troughs may be considered if water availability is controlled
  • ensuring livestock have access to roughage such as hay. Bloat oil can also be applied to this roughage
  • incorporating bloat resistant legumes such as Lotus corniculatis into pasture mixes.