Relationship of blood loss to worm numbers, biomass and egg production in Haemonchus infected sheep

Abstract

Chromium51 labelled erythrocytes were used to measure blood loss in sheep infected with either H. contortus, H. placei or the F1 of their reciprocal cross hybrids (H. contortus males × H. placei females = CXP, H. placei males × H. contortus females = PXC). CXP consisted of sterile males and semi-sterile females and sheep infected with this hybrid had nil egg counts; while PXC consisted of semi-sterile males and females and their hosts had some eggs in their faeces. Immediately after their blood loss was estimated the sheep were killed and their worms counted. One hundred male and 100 female worms from each sheep were dried at 60°C overnight and then weighed to give an estimate of the biomass in each infection. Total daily egg production was calculated from egg counts made on 3 random 2 g samples from the 24 h faecal collection. The relationship of the log blood loss to log worm number, to log biomass of infection in each sheep and to log total egg production in the parental species was linear. Biomass was no better an estimator of blood loss than was worm number. There was no improvement in the estimation of blood loss by regressing the male and female worms separately. In all of the analyses, there was no improvement by regressing H. contortus and H. placei or their hybrids separately. It appeared that egg production was not a major factor in the requirement for blood by Haemonchus. The size of individual female worms was negatively correlated with the number of worms in the infection. The linear nature of the relationship of blood loss to worms number, worm biomass and worm egg production indicated that sheep have very little control of blood loss and that the limitation of the pathology of Haemonchus infections is likely to be exerted at the establishment stage of the infection.