Pathophysiology of ovine fascioliasis: The influence of dietary protein and iron on the erythrokinetics of sheep experimentally infected with Fasciola hepatica

Worm-free sheep were fed diets with a high or low protein and iron content and infected with 1,000 F. hepatica metacercariae. The adult fluke burdens of the sheep on each diet were similar, but animals on the poorer plane of nutrition developed an earlier and ultimately more severe anaemia and as a result had to be necropsied earlier. By measuring the attendant changes in blood volume and erythrokinetics, it was found that the underlying cause of the anaemia in all animals was a combination of haemodilution, intra-hepatic and biliary haemorrhage, and its earlier appearance and faster development in the poorer-fed group was a refelection of the earlier onset of these changes in association with a faster rate of fluke migration. The ultimate degree of anaemia was not related to the severity of biliary haemorrhage, but rather to the animals' erythropoietic capacity. This was substantially lower in the sheep maintained on the poorer diet, which unlike their better-fed counterparts, became iron deficient by virtue of their inability to replace from the diet iron lost in the faeces as a result of haemorrhage. It was concluded that this difference was primarily a reflection of the better appetite and hence iron intake of the supplemented sheep, but differences in the efficiency of dietary iron utilization, possibly related to protein intake, may also have been involved.In a further experiment involving sheep infected with 600 metacercariae, there was no evidence of haemodilution. When provided with a diet of high protein and iron content, these animals were able to maintain constant, albeit reduced PCV values in the face of substantial biliary haemorrhage. However, when switched to an inferior diet, the same degree of haemorrhage produced a sharp fall in PCV, suggesting that erythropoiesis was adversely affected by reduced protein and iron intake.