The responses of two ecotypes of Nigerian West African Dwarf goat to experimental infections with Trypanosoma brucei and Haemonchus contortus

The West African Dwarf (WAD) goat from the humid zone of Nigeria is known for its trypanotolerance as well as for its resistance and resilience to Haemonchus contortus (haemonchotolerance). Another ecotype of WAD goat with a larger body size is found in the drier savanna zone of the country. We tested the hypothesis that the latter is less trypanotolerant, and less haemonchotolerant than the former ecotype because they have been less exposed to these infections and because of the likelihood of introgression of alleles for parasite susceptibility into the latter from neighbouring parasite-susceptible Sahelian genotypes. Two controlled experiments were carried out. In the first, we compared the responses in 8–9 month old kids of both ecotypes to subcutaneous infection with 5 × 10⁶ Trypanosoma brucei. Infection in both ecotypes was characterised by (i) prepatent periods of 3 days; (ii) a modest peak parasitaemia 4–5 days post infection (pi), followed by rapid clearance of parasites from the blood to microscopically undetectable levels from D11 or D12 until the end of the experiment on D30 pi; (iii) a sharp but transient drop in PCV following peak parasitaemia, with no other clinical evidence of anaemia; and (iv) normal growth and a small but weakly significant change in body temperature. In a second experiment we infected groups of goats of both ecotypes with 6000 L3 of H. contortus. This infection also produced no significant changes in the PCV and body weight of the goats. Only a small percentage of the inoculum was recovered from both ecotypes at necropsy on D18 pi (Mean % recovery ± SE = 3.29 ± 0.61 for humid zone and 6.83 ± 2.72 for savanna goats) and there was no significant difference in their worm burdens. On the basis of these results we reject our hypothesis and conclude that the savanna WAD ecotype exhibits comparable, strong degrees of trypanotolerance and haemonchotolerance to its humid zone counterpart.