REPEATED INFECTIONS WITH HAEMONCHUS-CONTORTUS AND TRICHOSTRONGYLUS-COLUBRIFORMIS IN DAIRY GOATS - COMPARISON OF RESISTANT AND SUSCEPTIBLE ANIMALS

A total of 70 strongyle-free French Alpine dairy goats were exposed to a combination of sequential and challenge infections with Haemonchus contortus and Trichostrongylus colubriformis third-stage larvae. The s equential infection consisted of three inoculations at 50-day interval s, each infection being abbreviated by anthelmintic treatment at 40 da ys postinoculation. The challenge infection, composed of the same nema tode strains, was undertaken 2 months later, when goats were at their Ist month of lactation. Fecal egg counts (FECs), packed cell volumes ( PCVs), pepsinogen concentrations, inorganic phosphate concentrations? and peripheral eosinophil numbers were measured at 30-40 days after ea ch inoculation. Goats were defined as being resistant or susceptible a ccording to their level of nematode egg output following the first ino culation. Significant differences in FECs were recorded between the tw o groups throughout the further inoculations and the challenge infecti on. The reliability of FECs was supported by the high repeatability va lues found within and between infections. With regard to blood constit uents, only PCVs related to H. contortus infection showed values that differed significantly between the two groups, resistant goats having higher PCVs after the first and the third inoculations than did suscep tible animals. However, this difference was not detectable after the c hallenge infection. The milk production yield for the current lactatio n was significantly lower in the resistant goats. Moreover, resistant animals exhibited constantly greater body condition scores as compared with susceptible animals. These results indicate that the individual responsiveness of dairy goats to experimental nematode infection can b e estimated on the basis of FECs and PCVs (for H. contortus) and is ne gatively related to the level of milk production of the animals.