Pathological changes associated with Oesophagostomum columbianum infestations in sheep: Haematological observations on control worm-free and experimentally infested sheep.

Abstract

Variations in the numbers of erythrocytes and white cells within the blood of sheep given various doses of Oesophagostomum columbianum larvae were studied over a period of 10 weeks.

The sheep showed losses of red cells and haemoglobin, and the packed cell volume was diminished after infestation with O. columbianum. These effects increased in severity as the infesting dose was increased; the resistant state of the host also affected the blood picture.

In all infestations the calculated absolute values for the blood, i.e. mean corpuscular haemoglobin (MCH), mean corpuscular volume (MCV), and mean corpuscular haemoglobin concentration (MCHC), did not significantly change except in the heavier infestations, where MCV increased for a time.

The type of anaemia which predominated throughout these experiments was normocytic-normochromic. Where the MCV increased for a period, the anaemia was of the macrocytic-normochromic type. During the first infestation with 2000 larvae the anaemias tended to become microcytiohyperchromic, but these changes were not significant.

Gross observations on the gut indicated that one of the factors influencing the development of anaemias was the extensive tissue damage caused by the larvae, which resulted in chronic bleeding from the mucosa. This suggestion was supported by the fact that anaemias also developed during second infestations when there was no adult worm population.

The white cell counts from a number of these sheep were also recorded. The most significant changes occurred after second infestation, although a general increase was noted after all first infestations as well; prominent increases occurred in the agranulocytes and the eosinophil leucocytes. The neutrophil leucocyte counts fell throughout all the infestation.

All the normal values obtained for the haemoglobin concentration, packed cell volume, red cell counts, MCV, MCH, and MCHC and white cell counts compared favourably with the values cited by other workers.