Ms Caroline Garvan:

The reason we have the increased resistance is because of the way we have been using these medicines. That is the bottom line, really. There are certain practices that need to be followed to use these medicines responsibly and to get the best possible outcome. There are practices such as refugia where not all the animals in the herd are treated at the one time, so a naive population of parasite is maintained on the farm. Grazing management is key. One does not dose and move to a clean pasture. These parasites only affect the younger animals, so it is all about the grazing system. There is also the quarantine element when buying in animals. They should be quarantined so that they are not immediately exposed to the parasites within a herd on the pasture.

It is a very complicated dynamic, but the bottom line is the more we use the medicines, there will be a certain development of resistance. There is also the issue if we continue to use them incorrectly or at the wrong time. For instance, a white drench must be used for treating nematodirus in sheep. It should not, however, be used later in the season because it will not affect adult worms. All these things must be borne in mind. If best practice is not followed, resistance continues to develop over time, as we have seen with antimicrobials. The more a treatment is used, the more whatever is being treated develops mechanisms to become resistant.