Selective mating of Perendale sheep for increased or reduced susceptibility as lambs to an experimental challenge with Haemonchus contorus commenced in 1986. Four years later changes were assessed by monitoring faecal nematode egg count (FEC) in ewes and their progeny. In the absence of drenching, mature flock ewes were given 7000 infective larvae of H. contortus and 3000 larvae of Trichostrongylus colubriformis in mid May 1990 after mating. FEC were monitored at regular intervals during pregnancy and 4 times during the periparturient period. Ewe and ram lamb progeny were faecal sampled on 5 occasions between weaning (November 1990) and May 1991. Lambs were drenched at most sampling dates. All stock were grazed across pasture contaminated previously with mixed parasite populations. Adult ewes selected as lambs for Resistance (low FEC) shed fewer eggs than Susceptible (high FEC) line ewes throughout pregnancy, 2 weeks pre- and 3, 6 and 9 weeks post-parturition. At the periparturient peak, approximately 3 weeks after lambing, Low FEC line ewes maintained FEC which were only 25% of those in the High FEC line. Lambs from the Low FEC line had significantly lower FEC than their High counterparts on 3 of 5 sample dates (P<0.01). At the final sample date (30 April 1991), there was a 10-fold difference in mean FEC between extreme sire groups. Bulked faecal cultures demonstrated that Haemonchus and Trichostrongylus were the dominant genera.
Proceedings of the New Zealand Society of Animal Production, Volume 52, , 25-28, 1992
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