Abstract :
Sustainable control of nematode parasites in small ruminant production is a worldwide
ambition. Development of anthelmintic resistance can severely impair small ruminant production.
A practical approach to reduce selection pressure for anthelmintic resistance is to
treat only a proportion of the flock (Targeted Selective Treatment), leaving a proportion of
the nematode population untreated. The aim of this study was to compare the sustainability
and efficacy of a performance-based marker, the Happy FactorTM, a monitor of nutrient
utilisation efficiency, with a routine whole flock anthelmintic treatment. In a commercial
flock in the South West of Scotland, 183 Texel cross lambs were split into two matched but
co-grazing groups: one group managed as routinely for the farm (RT group) and the other
subjected to targeted selective treatment (TST group). All lambs from the RT group were
drenched every 6 weeks during the grazing season, while anthelmintic administration in
the TST group was restricted to animals that failed to reach pre-determined weight gain
targets, based on an estimate of their efficiency of gross energy utilisation. Animal performance
and parasitological data were recorded every two weeks. In the 20 week period of
the study, anthelmintic treatments were reduced by approximately 50% in the TST group
compared to a routine anthelmintic administration that would have been applied, whilst
epg counts were always <500 throughout the study in both groups. Finally, there was no
discernible difference in the mean bodyweight gain between the two groups.
