Response to challenge infection with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats. Differences between high and low-producers.

The objective of the study was to analyse the influence of the level of milk production in dairy goats on the ability to develop resistance to gastrointestinal nematode infection. Two groups of 50 goats were initially exposed (Group 'Previously Infected' PI) or not exposed (Group 'Not Previously Infected' NPI) to repeated infections with a mixture of Haemonchus contortus and Trichostrongylus colubriformis. After anthelmintic treatment, goats from both groups remained free of parasites for 2 months around kidding. One month after kidding, 24 lactating goats in each group were challenged with Haemonchus contortus and Trichostrongylus colubriformis. Parasitological, pathophysiological and milk production parameters were then examined fortnightly for 3 months following challenge. Within the PI and NPI group, the response to challenge was compared between the 25% goats exhibiting the lowest level of milk production and the 25% with the highest level of production. In the low producers, previous contact with the parasites was associated with a decrease in egg excretion which was not apparent in the high producers. Previous exposure to parasites was also associated with more severe pathophysiological disturbances in the high producers. Lastly, the response to challenge also induced more severe depression in milk production after previous infection in the animals with the highest productive potential. These results confirmed that the level of milk production in dairy goats could influence the resistance and/or resilience to parasitism with more severe consequences detected in the high producers. In addition, the results suggest that such differences could in fact be mainly related to differences in the host response to parasites.