Bloat is a form of indigestion marked by excessive accumulation of gas in the rumen. Immediately after cattle consume a meal, the digestive process creates gases in the rumen. Most of the gases are eliminated by eructation (belching).

Any interruption of this normal gas elimination results in gas accumulation or bloat. Bloat can be caused by:

• a condition secondary to acidosis indigestion,
• certain proteins in forage,
• the amount, rate of intake, and coarseness of the roughage,
• rate of digestion of grains as a result of processing (grinding too fine),
• host-parasite reaction following grub treatment choking,
• enlargement of the lymph nodes between the lungs, which can compress the esophagus or interfere with the function of the vagus nerves, or
• an inherited tendency for bloat.

Trapped gases that are not eructated (belched) may form a foam or froth in the rumen that further prevents elimination of gases. Froth can be formed by many factors resulting from interactions among the animal, rumen microorganisms, and differences in plant biochemistry. Bloat may also be present with no evident froth or foam, described respectively as frothy (pasture) bloat and non-frothy (dry) bloat. The most common is frothy bloat where gas builds up in a foam or froth above the liquid/semi-liquid fraction of the rumen content and the normal belching is inhibited.

Preventing bloat is desirable not only to reduce deaths but also to reduce the negative effect of bloat on cattle performance. Pasture (frothy) bloat can occur in animals grazing wheat pasture or lush legumes (alfalfa, ladino, white clover) or being fed green-chopped legumes. Feedlot (dry) bloat usually refers to bloat in cattle fed high-grain rations that may or may not contain legume forage. It often occurs secondary to acidosis and/or rumenitis. Cattle consuming feedlot diets may have bloat caused by the grain portion being ground too finely. Fine-ground grains are digested rapidly, causing rapid fermentation and gas production.

Visual signs of bloat in cattle include:

• distension of the left side of the animal as the primary sign,
• discomfort as indicated by stomping of feet or kicking at the belly,
• labored breathing,
• frequent urination and defecation, and
• sudden collapse.