Last month we brought you a fascinating blog post about the One Health approach written by the team at VirtualVet. Based in Ireland, VirtualVet uses technology revolutionise the recording of drug use and disease in livestock. As a result the team have a wealth of knowledge regarding animal health, and we are excited to share this with you through monthly blog posts. This month Caitriona explains the threat of anthelmintic resistance:


Anthelmintic resistance (AR) has become an ongoing problem for grazing animals. Farmers can contribute to control methods, helping delay the development of resistance.

This simple graph demonstrates the relationship between the performance of the animal and the increase in anthelmintic resistance. Source: http://www.scops.org.uk/what-is-resistance.html

Faecal samples taken 14 days after treatment with anthelimintics are required to check for the existence of eggs to see if treatment was effective. Faecal sampling gives greater feedback on individual animals or small groups, but results from bulk milk test screening can indicate the level of infestation in the herd. However, results from any sampling should be used in consultation with the vet, on herd health planning and preventative medicine use.

Unless we test for AR we would probably not notice lack of effectiveness of treatment until their numbers had increased to 50% or more of the total worm population in an animal. At this stage the anthelmintic used is killing so few worms, that animals are clearly not being effectively de-wormed.


There are a variety of strategies to tackle AR, for example methods to slowdown the process and interrupt the lifecycle of the parasitic worms should be utilised. The effectiveness of current treatments and reviewing current treatment plans should also be addressed. Farmers need to identify several factors to ensure the anthelmintic is administered accurately and to determine if the animal requires the treatment. These factors include identifying what type of worm is being treated, if the correct product is being used, and if the dosage administered is appropriate. Following these steps can contribute to effective anthelmintic treatment, and reduce the growth of anthelmintic resistance.