Bloat
A dangerous build-up of gas in the rumen that swells a cow's left side.
Also: ruminal tympany, frothy bloat
Bloat happens when the gas made by fermentation in the rumen cannot escape by belching. The left side of the animal swells, it becomes distressed and, if untreated, pressure on the lungs and heart can kill it. Frothy bloat, the commonest kind, occurs when cattle eat lush clover, lucerne or other legumes, which form a stable foam that traps the gas; free-gas bloat can follow a blockage of the gullet or a sudden overload of grain. Farmers prevent it by bringing cattle slowly onto rich pasture, mixing grasses with legumes and using anti-foaming treatments. A vet may release the gas with a stomach tube.