Nutrition and disease.

Mortality from digestive diseases in feedlot cattle is second only to that from respiratory diseases. Acidosis and bloat are the major digestive disorders and are likely to continue because of ongoing attempts to improve the efficiency of beef production by feeding more grain and less roughage. Subacute acidosis is probably the most prevalent form of acidosis in feedlots and is difficult to diagnose because of the absence of overt clinical signs. Ruminal changes in subacute acidosis are not as dramatic as those in acute acidosis. Also, the subacute form is not severe enough to induce systemic acidosis. Ruminal acidosis is also a predisposing factor for many other ailments in feedlot cattle such as laminitis, polioencephalomalacia, sudden death syndrome, and liver abscesses. Control of acidosis is achieved largely by sound nutritional management. Antimicrobial compounds (i.e., ionophores and nonionophores), have become management tools to impart stability to ruminal fermentation, modulate feed intake, and control acidosis. Bloat in feedlot cattle can be of free gas or frothy type. Frothy bloat is more common but is rarely the reason for bloat deaths. The economic impact of bloat results mainly from decreased animal performance. The etiology of bloat is complex and is the result of interactions between three major groups of factors: animal, dietary, and microbial. Presently, an effective method to control frothy bloat in feedlot cattle is not available. Ionophore antibiotics, particularly monensin, have been shown to be effective in decreasing the incidence and severity of bloat in cattle.