The anaemia produced by Haemonchus contortus was characterized by a marked reduction in haemoglobin concentration and packed cell volume, accompanied by a marked rise in the concentration of potassium in the erythrocytes [Ke+] and a fall in the concentration of sodium [Nae+]; total [Ke+ + Nae+] remained steady. Infection was associated with reduced food intake and a lowered concentration of plasma protein, but plasma potassium and sodium remained constant. During the first 10 weeks of the experiment both the infected and the control sheep developed an anaemia of unknown aetiology, characterized by raised [Ke+], [Nae+], and [Ke+ + Nae+] values, and plasma protein concentrations.The evidence presented seems to suggest that sheep of haemoglobin type A may harbour fewer worms than sheep with haemoglobin type AB following infection with H. contortus.

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The gene frequencies for high potassium and haemoglobin type A have been determined in flocks of Romney Marsh and Southdown sheep in New South Wales and these frequencies have been compared with those found in Great Britain.

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