A general physical examination should be performed including palpation, percussion, ballottement and paracentesis.
Differentiation is based on history (in particular the numbers affected, the suddenness of onset and feeding conditions) plus clinical examination and necropsy findings.
When viewed from the front or rear of the animal, distension may be unilateral, bilaterally symmetrical, asymmetrical or more prominent in the dorsal or ventral half, depending on the cause.
Passing a stomach tube, auscultation with percussion and ballottement to detect areas of gas and fluid, insertion of a trochar, rectal palpation (cattle) and examination of faeces may assist in deciding the cause and need for intervention.
Abdominal distension due to pregnancy is usually due to the presence of multiple foetuses or may be associated with pitting oedema due to fluid accumulation along the floor of the udder and adjacent tissues.
The rumen will distend after rapid engorgement on grain (grain overload) or slow accumulation over days of indigestible roughage (rumen impaction). If the distension is mainly gas, it will usually be due to free gas or froth in the rumen (gas cap or frothy bloat). If it is gas and fluid it may be due to a gastrointestinal accident such as torsion, obstruction or perforation of the abomasum or intestine. In goats, distension may be caused by intestinal tympany of enterotoxaemia.
Distension by fluid may be due to urine in a distended bladder or free in the abdomen after bladder rupture following urinary obstruction. Fluid may also be ascites if blood is chronically low in protein from parasites or undernutrition.
Hernias should be considered in sheep and goats because the abdomen is thin walled and easily traumatised.