Anaemia

Anaemia is defined as a deficiency of red blood cells or of haemoglobin, or both. In the export process it will most commonly be a deficiency of red blood cells resulting from blood loss, haemolysis or reduced red cell production in the bone marrow. Possible causes of blood loss are bleeding abomasal ulcers, parasitism such as haemonchosis, fascioliasis and ticks, injuries severing blood vessels or rupturing the liver or spleen, and surgical procedures such as dehorning, castration or spaying. Infections such as babesiosis and leptospirosis may cause intravascular haemolysis. Bracken fern poisoning may suppress the bone marrow.

The blood volume of cattle is approximately 6% bodyweight (24 L for a 400 kg steer). In acute bleeding events, the first signs of weakness, dyspnoea and mucosal pallor occur when 15 to 20% of the blood volume is lost. Shock, collapse and death occur when 30 to 40% blood volume is lost.

Necropsy findings will always include pallor of the carcase. Jaundice, petechial haemorrhages, watery blood, ruptured organs, dark urine, splenic enlargement or black faeces may be present, depending on the cause. Note that petechial or ecchymotic haemorrhages affecting the heart are a normal necropsy finding, particularly in euthanised cattle. Haemorrhages elsewhere in the body are probably abnormal and may be associated with generalised viral or bacterial infections or a clotting defect.

Where the cause of anaemia is not obvious, laboratory diagnosis may be assisted by specimens of faeces for parasitology, and haematological examination of samples such as blood, spleen and bone marrow.