Genetic resistance to gastro-intestinal parasitism in Creole goats : effects of tropical environments on genetic expression of the trait

Abstract

The first objective of this study was to show theexistence of genetic variability in Creole goat  resistance to natural infection by gastro-intestinal nematodes. The aim was to introduce this recently identified trait in genetic improvement programmes. The second objective was to verify whether or not the same traits of resistance were expressed under favourable nutritional breeding conditions. In this way, the resistance of 13 Creole bucks was estimated through the average performance of their offspring bred on 2 grazing systems. Kids were tested at 6 and 10 month old. Haemonchus contortus and Trichostrongylus colubriformis were the main parasite species in the pasture. A significant genetic variability in each environment for the 6 month old kids was shown. Genetic correlation between the different resistances expressed under favourable nutritional conditions was + 0.83 (P < 0.001). The rankings of the bucks were not significantly correlated between favourable and unfavourable nutritional conditions. This suggests that the biological mechanisms of resistance expressed under favourable and unfavourable nutritional conditions, are governed by different genes. No genetic variability was found when resistance was measured for the 10 month old kids, due to a low infection rate.