Experimental infection of Ethiopian highland sheep by different infective doses of Haemonchus contortus (L3): haematological and parasitological parameters, serum protein concentrations and clinical responses

Abstract

The study was conducted to examine changes in haematological and their eventual associations with parasitological parameters and clinical responses in experimentally infected Ethiopian highland sheep by increased doses of Haemonchus contortus infective larvae (L3). A total of 24 male sheep were allotted in to four equal groups: a single dose of 2 000, 4 000, or 6 000 infective larvae of Haemonchus contortus (L3) was orally administered to animals from the first 3 groups whereas the last group not treated and served as negative control. The faecal egg count (EPG), the body weight as well as haematological parameters (haematocrit and eosinophils counts) and proteinaemia were measured throughout the experimental 13 weeks long period and worm burden and sex ratio were assessed at necropsy. The infection was confirmed by the occurrence of the faecal egg excretion and by the presence of adult worms in abomasums. All Haemonchus infected sheep exhibited a progressive and severe anaemia characterized by marked reductions of haemoglobin concentration and haematocrit, associated with weight loss and growth retardation and on the contrary with strongly and transiently increased eosinophil population compared to control animals (P<0.01). Except for proteinemia, parasitological, clinical and haematological alterations were significantly proportional to the parasite load. Moreover, the eosinophil counts, the adult worm population and the egg excretion positively and significantly correlated together, whereas they were negatively associated with body weight, proteinemia and the other haematological parameters. All experimentally infected animals appeared to be highly susceptible to the infection by Haemonchus contortus and the severity of the haemonchosis was clearly related to the infective dose.