Response to challenge infection with Haemonchus contortus and Trichostrongylus colubriformis in dairy goats. Consequences on milk production.

The objective of the study was to examine the ability of dairy goats to develop a response to nematode parasites of the digestive tract after a previous contact with the worms. One hundred dairy goats were initially divided into 2 groups. One remained free of parasites (not previously infected: NPI). The second group was infected thrice at 50 days interval with a mixture of Haemonchus contortus and Trichostrongylus colubriformis (previously infected: PI). After this initial exposure to nematodes, the goats were drenched with fenbendazole to eliminate the worms and remained free of parasites for 2 months around kidding. One month after kidding, 24 lactating dairy goats from each initial group were challenged with a mixture of H. contortus and T. colubriformis and parasitological, pathophysiological and milk production parameters were measured fortnightly to assess the effects of challenge infection and the response of the goats. No difference in parasite egg excretion was found between group NPI and PI after challenge infection. Similarly, no difference in worm counts was detected in 5 culled goats from each group killed one month post challenge. In contrast, differences between both groups were detected when considering the pathophysiological parameters (packed cell volume, inorganic phosphate and pepsinogen concentrations) with consequences of infection being more severe in the previously infected animals. Moreover, the milk production was also depressed in the PI group when compared to the NPI one. These results indicate that the response developed by adult dairy goats after the challenge infection was unable to limit the worm populations but could have pathophysiological repercussions and consequences on production.