Breeding sheep in New Zealand that are less reliant on anthelmintics to maintain health and productivity

Abstract

Breeding sheep that are less reliant on the use of anthelmintics to maintain acceptable health and productivity is one of several options that may assist farmers to manage the growing anthelmintic-resistance problem in New Zealand and meet consumer demands to minimise drug usage in livestock. Although it has been known for many years that genetic factors contribute to the ability of sheep to cope with roundworm challenge, attempts to selectively breed for such factors have occurred only recently. Two host traits, 'resistance' and 'resilience', are thought to be involved in limiting the deleterious effects of roundworms on the health and productivity of sheep, and the associated need for treatment with anthelmintics. Over the last decade, considerable advances have been made in our understanding of the feasibility and implications of breeding for these traits under practical conditions. The experimental breeding lines developed as part of this research are now proving to be a valuable resource for further work directed at identifying genes and/or genetic markers associated with host resistance and understanding the mechanisms of host immunity to nematode parasites in ruminants. This review provides an up-to-date summary of the results of research in this field, with particular reference to dual-purpose sheep in New Zealand, and describes how this information is being applied in practical breeding programmes.

Genetic parameters and relationships of faecal worm egg count with objectively measured wool traits in the Tygerhoek Merino flock

“…The exception to this trend was observed for wool weight traits, where FEC was unfavourably related to both GFW and CFW. This antagonistic relationship between wool weight and FEC was also observed in New Zealand (Bisset et al, 2011). However, the magnitude of these relationships in the current study is such that it ought to be feasible to simultaneously improve FEC and wool weights.…”

The role of targeted selective treatments in the development of refugia-based approaches to the control of gastrointestinal nematodes of small ruminants

“…Resilient animals continue to perform whilst under parasite challenge and therefore require less anthelmintic treatments than non-resilient animals in any given season (Bisset et al, 2001a). Furthermore, lambs in temperate regions can develop significant protective immunity to some helminth species by the end of their first grazing season (Waller and Thomas, 1978;Waller and Thomas, 1981), thereby effectively controlling their worm burdens.…”

Direct and correlated responses to selection for high or low faecal nematode egg count in Perendale sheep

“…Besides the obvious difference in sheep breed, climatic conditions in Australia and therefore the epidemiology of parasite infection are different, with overall levels of challenge likely to be higher in New Zealand. Also, the Australian studies have tended to measure responses to single-species artificial challenge infections whereas the New Zealand studies have involved predominantly multi-species natural infections (Woolaston & Piper 1996;Bisset et al 2001a;Woolaston & Windon 2001). It remains unclear which of these factors may have contributed to the different correlated responses measured.…”