The concept of leaving parasites unexposed to treatment (“in refugia”) and thus maintaining susceptible alleles within the population is considered to be of critical importance in slowing the evolution of resistant parasite strains. The Happy Factor™ method involves predicting an individual weight target for growing lambs and only treating each animal which fails to achieve this level of productivity.
Scottish researchers conducted a study to determine the viability of the Happy Factor™ weight-based targeted selective treatment (TST) on several commercial farms in Scotland. The effect of TST strategy on lamb productivity and the number of anthelmintic treatments was investigated.
There was no evidence that mean body weight or growth rate was different between TST and routinely treated (RT) groups. TST had negligible unfavorable effects on the average growth of lambs for most of the farms. All commercial farms used significantly less treatments per animal anthelmintic in lambs following TST (1.12 vs. 1.34).
Conclusion: This study suggests that TST is a viable means of controlling parasitic disease without incurring production losses.
Source: Veterinary Parasitology, March 2016. Read abstract