Performance of progeny of Romney rams selected for productivity under nematode challenge : growth and faecal egg counts under conventional and anthelmintic free management systems.

The performance of lambs, two tooths and mixed age ewes, sired either by rams selected for productivity under high nematode challenge (PC) or by commercially-bred rams selected for productivity under minimal challenge (PM), was compared under conventional and anthehninticfree management regimens. This work was part of a larger systems comparison run over five years to examine the risks and constraints of a chemical-free (CF) approach to livestock farming in relation to a conventional (C) system. Parasite challenge encountered by sheep on the CF system was consistently higher than for those on the C system. Presumably, as a result of this factor, conventionally managed sheep were on average heavier than CF sheep until 24 months of age. Progeny of PC sires out-performed progeny of PM sires in the CF system at 8 months and in the C system at 20 months. Except at 3 months, when PM progeny had higher faecal egg counts (FEC) than PC progeny, there was no significant difference in FEC between the two progeny types.