Worm Control in Cattle

A recent assessment of the economic burden of major gastrointestinal parasites in cattle and sheep, estimated an annual cost for the 18 participating countries of €1.8 billion. Eighty-one percent of this cost was due to lost production and 19% was attributed to treatment costs. Furthermore, the cost of gastrointestinal nematode infections with resistance against macrocyclic lactones was estimated to be €38 million annually (Charlier et al., 2020). Clearly there is scope to improve the management of worms at the herd level. However, whilst awareness of sustainable methods of parasite control are well described in sheep, the same is not the case for cattle. In light of this, a recent position statement has been published by the British Cattle Veterinary Association (BCVA) accessible here: New BCVA Policy Prioritises Parasite Control. It advocates a shift away from routine “strategic” dosing to a more targeted approach.

“Strategic treatment” describes the routine dosing of first-season grazers at specific intervals of time based upon the predicted life cycle of worms, to minimize adult burdens and their consequences whilst allowing the development of immunity which allows us to minimize treatment when they are adults. Whilst this approach works well, it may promote the development of anthelmintic resistance, making worm control in the future more difficult. Clearly anthelmintic use is still needed, but it must be more discriminating.

In light of this; two new approaches to worm control in cattle have been suggested – “targeted treatment” and “targeted selective treatment”. Such approaches aim to suppress parasite populations below those that have an impact on production, whilst ensuring a pool of susceptible worms (“refugia”) exist to minimize the development of resistant genotypes.

Targeted treatment may be defined as the treatment of a whole group of animals based on knowledge of parasite risk or following diagnostic information and estimation of infection severity – this might be a pooled worm egg count 4-8 weeks after turnout, measurement of growth rate data, or milk or blood tests such as serum pepsinogen at housing. In dairy herds, bulk milk anti-ostertagia antibody levels may indicate the current worm burden in milking cows. By delaying treatment until it is actually required, unnecessary treatment and the development of resistance can be minimized. However, practically implementing such an approach requires diligent monitoring to avoid (sub)clinical effects of worms on growth or milk production from occurring.

Targeted selective treatment is defined as treatment only of individual animals likely to benefit the most from treatment within a group based upon a determinant criterion – e.g. O’Shaughnessy (2015) performed this approach based upon 3x weekly measurement of individual worm egg counts and treatment of individuals with a count >200 in suckler calves and dairy cows. Whilst the results were promising, this approach isn’t especially practical, and for most farmers targeted treatment may be the most appealing route to take.

Policy statements such as those released by the BCVA highlight that there is going to be a move away from strategic treatment of cattle to a more refined approach, such as those described above. These will be farm specific, and to maximize animal performance will require diligence and attention to detail. If you need any help, our team of vets will be more than happy to discuss how to optimize anthelmintic use on your farm!