The use of haemoglobin, packed-cell volume and serum sorbitol dehydrogenase as indicators of the development of fascioliasis in sheep.

Haemoglobin, packed-cell volume and serum sorbitol dehydrogenase activity were studied in 8 groups of 3 Corriedale weaner wethers artificially infected with a range of fluke burdens. Data from haemoglobin and packed-cell volume measurements were analysed using regression procedures. All parasitised groups exhibited a decrease in haemoglobin and packed-cell volume compared with the control group. The rate of this decrease was approximately linear, and dependent on the size of the fluke burden. Prediction equations for the rates of decrease of haemoglobin and packed-cell volume in fluke-infected sheep are presented. Death occurred when haemoglobin fell below 5 g 100 ml-1, and packed-cell volume to 15%. Anaemia became profound in sheep infected with more than 346 flukes and these sheep died 56-63 days after infection. Serum sorbitol dehydrogenase activity exhibited several peaks, before and after Week 12 post-infection, when flukes should have been present in the bile ducts. Reason for the activity later than Week 12 was not clear, although stress or immune responses may contribute. Haemoglobin and packed-cell volume may be useful in predicting the size of fluke burdens when the duration of the infection is known, and may indicate that time of death of infected sheep. Sorbitol dehydrogenase is an unreliable indicator of the size or the duration of fluke burdens.