Cases of congestive heart failure may occur in the export process.
The three most likely causes are valvular endocarditis, traumatic pericarditis and ionophore poisoning. Determining cause is important because it may have implications for other cattle.
Valvular endocarditis develops most commonly on the tricuspid valve (right atrioventricular valve) in cattle. The condition is generally preceded by a bacteraemia resulting from an infection located in a distant tissue or area (skin wound or infection of lung, gut, tooth root, joint surface or mammary gland). Bacteria can then lodge on the tricuspid valve and develop into the classic vegetative lesion, interfering with valve function and resulting in valvular insufficiency.
Traumatic pericarditis develops most commonly when a nail, needle or piece of wire is swallowed in hay or chaff. Foreign bodies often lodge in the reticulum and digestive contraction may then result in penetration of the reticular wall, the diaphragm and the adjacent pericardial sac. The sac then fills with a fibrinopurulent inflammatory effusion or blood that compresses the heart (cardiac tamponade).
Ionophores like monensin and lasalocid are antibiotic feed additives that in toxic amounts, cause myocardial necrosis. Toxicity may occur as a result of errors in pellet formulations or uneven mixing of added premixes. Severe damage to the muscle of the heart interferes with normal contractions.
Clinical Signs and Diagnosis
Heart failure is associated with oedema of the brisket and submandible, marked distension and pulsation of the jugular vein, diarrhoea, laboured respiration, and reluctance to move. Affected animals may collapse and die if forced to move. At necropsy there is a large amount of fluid in the thorax, abdomen and pericardium, the liver is swollen and congested with an accentuated lobular pattern, and there is oedema around the kidneys and in the mesentery. Pericarditis is recognised distension of the pericardium with fibrinopurulent pus and a nail, needle or wire may be found in or near the reticulum. Valvular endocarditis is recognised by the presence of a vegetative growth on a heart valve. Ionophore toxicity is recognised by areas of paleness and pallor on the epicardium, especially of the left ventricle, extending into the myocardium.
The damage to the heart and the debilitating symptoms are irreversible, hence salvage slaughter or euthanasia is indicated for all cases of congestive heart failure.
Diagnosis of traumatic pericarditis or ionophore toxicity may require withdrawal of feedstuffs potentially contaminated with nails, wire or ionophores. Manufacturers should be notified in case other batches are affected. Valvular endocarditis is rare and impossible to predict. Systems of early detection and aggressive treatment of infections with antibiotics is good export practice to prevent this and other complications of infections.