Goat production is widespread in the tropics. Goats are very susceptible to gastrointestinal nematode infection, but there is less evidence of their genetic resistance. Genetic resistance of Creole goats to gastrointestinal nematodes has been studied at Guadeloupe in the French West Indies since 1995. The objective of this research was to investigate genetic variation for resistance to gastrointestinal nematode infection, in order to introduce this trait into breeding schemes. Genetic variability was assessed within a Creole experimental flock. Forty-nine sire groups were characterized at weaning and 55 during fattening after weaning. Kids were naturally infected, mainly by Haemonchus contortus and Trichostrongylus colubriformis. Fecal egg counts were determined once at weaning and every 6 and 7 wk after drenching during fattening. Blood samples were collected every 7 wk during fattening for determination of packed cell volume. Live weights were recorded at weaning and at the beginning and middle of every infection period during fattening. Genetic parameters were estimated using the REML for multivariate animal models. The heritability estimate for transformed fecal egg count was 0.37+/-0.06 at weaning. During fattening, it increased from 0.14+/-0.05 at 4 mo to 0.33+/-0.06 at 10 mo. Heritabilities of packed cell volume ranged from 0.10 to 0.33. At weaning, maternal heritability of fecal egg count reached 0.26 and direct heritability 0.20. After 6 mo of age, maternal effects were found to be unimportant for fecal egg count and packed cell volume. Live weights presented significant genetic variability. Genetic relationships between fecal egg counts and live weight in infected pastures were never significant. Genetic correlations between packed cell volume and live weight decreased from 0.47 to 0.10 from weaning to 10 mo of age. These results demonstrated the feasibility of breeding for improved resistance to nematodes in Creole kids.

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The study was undertaken in a Creole goat flock at INRA-Gardel in Guadeloupe, to evaluate the opportunity to use artificial selection as a means of controlling gastro-intestinal infection during early lactation. The flock grazed all year on Digitaria decumbens pastures. Faecal and blood samples were taken from kids at 11 months of age and from does at kidding before drenching (week 0) and at weeks 4 and 6 after kidding. Faecal egg counts (FEC) were estimated using a modified McMaster method. Blood samples were used to determine packed cell volume (PCV) and eosinophil concentrations (EOS) values. Haemonchus contortus, Trichostrongylus colubriformis and Oesophagostomum columbianum were the main strongyle species identified in faecal cultures. The data came from 1092 litters obtained from 688 does sired by 142 bucks and 413 dams. Variance and covariance components for genetic and residual effects were estimated with multivariate animal models using the restricted maximum likelihood VCE package. Repeatability and overall heritability for FEC during the post-partum period were 0·17 and 0·10±0·02. The genetic correlations between FEC and PCV were −0·56±0·11 at 4 weeks after kidding and −0·79±0·13 at 6 weeks after kidding. The genetic correlations between FEC and EOS were 0·37±0·15 at 4 weeks after kidding and 0·68±0·17 at 6 weeks after kidding. Hence, does that contributed least to pasture contamination during the postpartum period also had low EOS and high PCV breeding values. The genetic correlations between FEC measured at 11 months of age and FEC during periparturient period ranged from 0·57±0·12 to 0·76±0·16. Therefore, breeding goats for increased resistance during the post-weaning period will lead to a less marked and less persistent rise in doe FEC during early lactation. The epidemiological implications of this selection have to be quantified in terms of lower pasture contamination, lower kid parasitism, and higher milk production of does.

The objective of this study was to evaluate the relationship of parasite-specific serum antibodies with the resistance status of Creole kids. The average breeding values on egg output predicted in a context of natural infection at 11 months of age were distant of 1.07 genetic standard deviation between resistant and susceptible animals. After drenching the animals were maintained worm-free during 1 month until experimental infection with 10,000 Haemonchus contortus infective larvae (L3). Enzyme-linked immunosorbent assay was carried out in serum samples to determine the level of IgG, IgA and IgE anti-H. contortus L3 crude extracts and adult excretion/secretion products (ESP). Parasitological and blood immunological parameters were measured on the 2 extreme groups. Despite the absence of any typical signs of haemonchosis, susceptible kids had more than 11 times higher faecal egg counts (FEC) at 35 days post-infection (d.p.i.) than resistant kids had. Levels of immunoglobulin against H. contortus L3 and ESP increased significantly after infection in both groups. However, no difference in the host immune response mediated by immunoglobulin against H. contortus was evidenced between groups. This finding suggests that, in goats previously infected by H. contortus, a degree of protection occurred and the phenotypic and genetic segregation in resistant and susceptible animals were not related to the humoral immune response. The correlation coefficients between FEC and IgE anti-ESP (r = 0.593; P < 0.05 was significant in both resistant and susceptible animals. Such correlation suggesting a hypersensitivity reaction dependent on worm prolificacy has never been described. This result needs further studies to understand the mechanisms underlying this observation. #

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