Drench resistance has been a key concern amongst sheep farmers, and it’s now quickly becoming a hot topic for dairy farmers too.
Data from faecal egg counts (FECs) taken from cattle poo samples, and shared by vets in a recent Wormwise forum, has shown Ostertagia worms that are resistant to triple oral drenches in 45% of tests!
It’s also known that Cooperia parasites are becoming commonly resistant to double and triple drenches.
Fonterra has picked up on this and has added a question about whether you are doing FEC tests in their Animal Welfare Plan – so it’s definitely something our farmers now need to start considering.
FEC testing for informed decisions
FEC tests count how many worm eggs are present in that poo sample, and therefore in the pasture that animal has been grazing. This helps determine if a drench is required or not and what product is appropriate.
They can also be used to test if a drench has worked effectively. A FEC taken 10-14 days after drenching will show if a drench has been successful as there will be very few eggs. However, resistance to one drench family does not indicate resistance to all drenches, so each different drench you try has to be tested separately.
If your calves are scouring, a FEC test can discover if the scours are due to internal parasites and if the calves need a drench.
Alongside testing, regular weighing of young cattle can indicate the success of a parasite management plan. A heavy parasite challenge will have a significant effect on growth rates of youngstock.
Fighting against drench resistance
Drenching more because an initial drench has not worked is not good practice for your cattle, your wallet, or the environment. There is no disagreement on how much internal parasites can affect calves, but a ‘drench every six weeks’ protocol is not the best policy to ensure long term effectiveness of drenches. Any worms that survive the drench will reproduce and spread resistant genetics.
One way we can lower the impact of internal parasites on our cattle, and the need for drenching, is to reduce the number of larvae in the grass they’re eating through farm management.
Some methods to reduce worm burdens in pasture are:
Grazing adult cattle on pasture between youngstock mobs grazing it, to ‘mop up’ the worms the young animals have produced. The adults themselves will produce very little, as they’ve already developed an immunity to internal parasites.
Cross-species grazing, such as running sheep through your youngstock’s pasture. Again, this means the larvae will be eaten before they can mature by animals that won’t be as affected.
Spelling pasture and then cutting it for silage – worms will be removed with the silage.
Cultivating pasture and turning the ground over – larvae will be killed when they are buried.
Planting new grass after a paddock has been in crop. This is a ‘clean’ pasture and will have very low parasite levels. When a pasture is ‘clean’, it is not recommended to drench stock and put them straight onto it, as this means there will only be drench resistant parasites on the pasture.
Another way to help limit drench resistance is the theory of refugia. This involves leaving a portion of your most well-grown calves undrenched each time, so there are worms with genetics not selected for drench resistance to mate with the resistant worms.
When effective drenching, refugia, and management practices like those above are used together, the overall number of parasites in your pastures can be really reduced.
Looking ahead
In the past, we have had a heavy reliance on drenches to control internal parasites in cattle, but we now cannot rely on them as we used to. It’s clear worms are developing resistance due to the high use of drench products on our farms.
We need to work together towards a more measured approach where drench is only one part of the solution, in order to continue growing calves into great cows in the years to come.
