Inhibited development of Haemonchus contortus in naturally acquired infections in sheep

Inhibited development of Haemonchus contortus in naturally acquired infections in sheep
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It is now widely recognized that inhibited development is a common feature of the life-cycle of many trichostrongyle nematode species, and forms an integral part of the epidemiological pattern of infections (Connan, 1968; Armour et al 1969a, b; Michel, 1971). Inhibition in Haemonchus contortus infections occurs at the early 4th larval stage and almost certainly provides the principal source of overwintering infection in most temperate regions (Blitz and Gibbs, 1972a, b). The maturation of previously inhibited H. contortus larvae can result in a significant contribution to the postparturient rise in the faecal egg counts of breeding ewes, providing the source of infection for the new season`s lambs (Connan, 1968; O`Sullivan and Donald, 1970; Blitz and Gibbs, 1972a). In New Zealand appreciable infections of inhibited H. contortus larvae have been recorded, both in predominantly young sheep (McKenna, 1973a), and in breeding ewes (Brunsdon, unpublished). Four factors have been shown to influence the induction of inhibited development in H. cortortus, namely, host resistance (Dineen et al 1965)) host diet (Poeschel ;and Todd, 1969), storage and consequent aging of infective larvae under constant conditions (Blitz and Gibbs, 1972a; McKenna, 1973b), and the effect on infective larvae of seasonal changes in environmental conditions…

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