Variability in the resistance of the Nigerian West African Dwarf goat to abbreviated escalating trickle and challenge infections with Haemonchus contortus.

The West African Dwarf (WAD) goat is known to be relatively resistant to infection with Haemonchus contortus. An experiment was carried out to assess variability in resistance under escalating trickle and single pulse challenge infection protocols. Thirty two 7-8 month old goats were subjected to trickle infection beginning with a thrice weekly dose of 100 L3 and increasing to 500 L3 by week 5, the last dose being administered on D30. Infection was abbreviated with fenbendazole on D32 and the animals challenged with 4000 L3 (=404-741L3/kg body weight) on D46 and necropsied on D81. The goats exhibited marked individual variability in faecal egg counts (FEC) and worm burdens (Wb). For convenience, we arranged the goats into FEC classes 1, 2 and 3, corresponding to peak counts of <1000, 1000-2500 and >2500 epg and Wb classes 1, 2 and 3, with counts of <50, 50-100 and >100 worms, respectively, broadly reflecting relatively resistant, intermediate and poorly resistant response phenotypes. Wb classes broadly reflected the FEC phenotypes and although there were no significant differences between the Wb of the FEC classes at necropsy, significant differences in FEC were detected when analysis was carried out only on Wb classes. There was also a significant positive correlation between FEC class on each of the days of challenge (D67 to D80) and worm burden at necropsy. In general, the goats showed strong resistance/tolerance to challenge, with more than 80% having Wb not exceeding 5% of the challenge dose, and only in class three goats were weight loss and anaemia detected in some animals. PCV and weight changes also closely reflected the FEC and Wb classes, with a significant negative correlation between each and Wb. Infection level did not significantly affect the sizes of either male or female worms and no significant difference was detected between the levels of circulating eosinophils in any FEC or Wb class. Overall, the data are consistent with the existence of a range of response phenotypes, which reflect variations in resistance of WAD goats to H. contortus infection, the genetic basis of which will be explored in future experiments.