Régulation des populations de Nématodes gastro-intestinaux ...

4 – DISCUSSION
Résultats
The resistance of Barbados Blackbelly sheep to H. contortus infections has been
successfully demonstrated in previous studies (Yazwinsky et al., 1980; Courtney et al., 1985a,
b; Notter et al., 2003). In our study, the resistance status of BBB lambs to Haemonchus
contortus was compared with INRA 401 breed. In the primary-infected BBB animals, the
lower number of worms in the abomasum, the reduced female worm size and number of eggs
in utero registered after autopsy strongly justify the drastic reduction in FEC compared to that
in INRA 401 group B. Complementary to this, is the retarded worm development as reflected
by the number of immature worms and the longer prepatent period in the tropical breed. The
lower FEC and worm establishment rate in the primary-infected BBB lambs compared to
corresponding INRA 401 group agrees with the reports of Aumont et al. (2003). After the
secondary infection, reductions in worm development and female fecundity observed in
INRA 401 lambs confirm our previous observations (Lacroux et al., 2006). Contrary to that
observed in INRA 401, the regulation of Haemonchus contortus infection was not improved
in challenged BBB lambs. This may suggest that the mechanisms governing resistance to this
parasite was efficient enough in the first exposure and was not enhanced during a secondary
infection. In a similar vein, Bahirathan et al., (1996) demonstrated that the Gulf Coast Native
suckling lambs developed resistance to H. contortus infection at first exposure. Moreover,
Amarante et al. (1999) observed that Florida Native lambs had lower FEC compared to the
Rambouillet breeds during first exposure to natural infection while there was no difference
between the two breeds of lambs after the second natural infection. This is in contrast to the
findings of Gauly et al. (2002) for Rhön and Merinoland lambs, Aumont et al. (2003) for
Blackbelly and INRA 401 lambs and Gamble and Zajac (1992) for St. Croix and Dorset
lambs, where animals infected for the second time have demonstrated better resistance and
breed differences than the primary-infected animals. While there are differences in the
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