Can body condition score be used to refine worm control

Anthelmintics are typically used to control worms and combat their deleterious effects on productivity, but inappropriate use has resulted in widespread resistance of worms to available anthelmintic treatment groups (Sutherland and Scott 2010). Adoption of new management strategies is required to slow the development of anthelmintic resistance. One potential strategy includes leaving a proportion of a flock untreated, which allows non-resistant (susceptible) worms to survive and thus slows the rate at which resistant genes accumulate in the worm population (Kenyon et al. 2009). The most appropriate indicator for selecting sheep that are to remain untreated is not clear. It is widely believed that sheep with a high body condition score (BCS) are better able to cope with worms (i.e., they have higher worm resilience) than sheep with low BCS, but little field research has been undertaken to verify this. Worm resilience is the ability to maintain an acceptable level of production despite a worm burden (Bisset et al. 2001). Figure 1 demonstrates a hypothetical relationship between BCS and worm egg counts (WECs) for worm resilient and non-resilient sheep.