Cause:
The cause has not been established in bison. Bloat is abnormal distension of the rumen and reticulum caused by excessive retention of gas in the rumen and reticulum. In order for normal eructation (burping) to occur, gas produced by fermentation in the rumen must coalesce into a bolus of free gas. When bloat occurs, soluble plant leaf proteins in the feed form foam in the rumen which will not coalesce into free gas. In cattle, bloat can occur with cows on pasture, or on dry feed. Pasture bloat is most often associated with leguminous plants (9). Bloat is not very common in bison but it has occurred (19).
Clinical signs:
Sudden death is a common finding in bison (19). In live bison there will be a large swelling on the left side of the animal, just behind the ribs. There may be increased respiratory rate, mouth breathing, and recumbency just before death. During the course of the disease, as the rumen enlarges pressure is exerted on the diaphragm making breathing difficult. Bloated bison that become too excited during handling for treatment will die.
Postmortem findings:
The rumen will be grossly enlarged and may still contain foam. There may be anterior congestion and posterior blanching of the carcass.
Diagnosis:
The diagnosis can usually be made from the clinical signs.
Treatment:
In cattle, mild cases of bloat may be treated by gently chasing (walking) the animal. This may be difficult in bison. Releasing the gas trapped in the rumen with a stomach tube may provide immediate relief. If the situation is life threatening the bison’s the rumen may be punctured from outside the body wall with a trocar or a sharp knife. Anti-foaming agents or surfactants such as mineral oil or dioctol sodium succinate can be administered orally.
If bison are on pasture when bloat is detected, they should, if possible, be moved off of the pasture and fed long grass hay until the bloating stops. If the bison are being fed dry leguminous hay, the hay should be changed to long grass hay.
Control:
It is not always possible to predict whether a pasture has the potential to cause bloat. Furthermore, the characteristics of any pasture can change in a very short period of time. In cattle, bloat is most commonly seen when lush, rapidly growing, pre-flowering leguminous pastures such as alfalfa are grazed. If a pasture was thought to be potentially dangerous, bison should be prevented from grazing it.
Monensin or salinomycin in the salt may reduce the incidence of bloat in cattle being grazed on legume pastures. The efficacy and safety of these products has not been established in bison.