Cattle Worm Resistance
June 2023

Drench resistance in sheep worms has becoming widespread over the last 20 plus years. This has really started to ramp up in the last 5 to 10 years, and we now have multiple properties in our area when only the novel active drenches (Zolvix Plus and Startect) are effective in controlling worms.

Things have been much slower to develop in cattle for a variety of reasons, but we have recently started picking up evidence of drench resistance in cattle worms also. This mirrors results from around the country – Gribbles Veterinary Pathology is reporting a growing number of cases where drench checks have failed after cattle have been drenched.

We are planning to work with Gribbles to do some surveillance work to get a better handle on how wide spread the problem is – this will hopefully be happening over the next 6 to 12 months.

In the mean time, if you want to check how things are going with your stock, collecting 10 fresh individual faecal samples from cattle 10 days after they have been treated is a good starting point. Make sure you collect samples into plastic pottles, not plastic bags or egg cartons.

Young stock (calves/R1s) are the best group to sample, as worms usually produce more eggs when they infect young stock than in older animals.

A count of zero doesn’t necessarily mean everything is fine, but it is a great start. Counts will obviously be zero if there are no worms present, but they will also be low if worms are not laying well. Worms don’t produce any eggs until they have matured in the animals gut, and their egg laying can also be heavily suppressed as cattle get older and their immune system puts pressure on the parasites.

Any faecal egg counts that are positive at 10 days after treatment are a concern, and usually indicate we need to investigate further.

If you have any concerns with your parasite control program, please get in contact.