Multi-faceted approach required for management of internal parasites | Beef + Lamb New Zealand
Animal Health

Multi-faceted approach required for management of internal parasites

Changes in land use or farm policies which result in predominance of young livestock could be recipe for disaster in terms of the development of drench resistance.
Tuesday, 13 August 2019

Ben Allott from North Canterbury Vets says while sheep and beef farmers are often encouraged to use triple active drenches to circumnavigate drench resistance issues, he says this ignores the changes that need to be made to address the fundamental issues that are creating the environment for drench resistance to occur.

Stocking policies that drive a reliance on chemicals to control internal parasites create the perfect environment for breeding drench resistant worms. These include intensive lamb finishing operations, particularly under irrigation and dairy heifer grazing.

A 50:50 cattle/sheep ratio is very effective at controlling internal parasites with each species effectively vacuuming up the other’s species-specific worm larvae off pasture.

Farming systems that target adult animals and run relatively low numbers of young stock, such as a hill country breeding and store properties, will also be at lower risk of developing drench resistance than finishing farms or farms with a dedicated intensive finishing system within them.

“When stocking ratios are out of balance and you have 100% sheep or cattle or just young animals, it forces you to use a lot of chemical to control parasites.”

Ben says refugia is absolutely critical to prevent drench resistance, but adds that it is a complex issue that can be difficult to fully understand.

Put simply, it is implementing stock management strategies that enable populations of drench susceptible worms to be maintained- critical to prevent drench resistance occurring. But these strategies need to be fully understood and implemented correctly and Ben encourages farmers to attend a Wormwise workshop to gain a clear understanding of this vital management tool.

“Refugia needs to be a focus.”

The provision of “clean” feeds- such as summer rape crops and lucerne stands - can allow the interval between lamb drenches to be extended as the 28-day rule is to prevent pasture recontamination, but again this is just another tool in a tool box to effectively control internal parasites and needs to be managed correctly.

Ben says Faecal Egg Counts (FEC) are not a simple measure of internal parasite burdens as other factors such as worm species and the feed the animal has been eating can have a big influence on egg counts. A low drymatter feed for example, will dilute the number of eggs.

“FEC is a convenient, easy tool but there are a lot of factors that influence it.”

“If you are relying on FECs to drive the timing of drench decisions you need to repeat them frequently otherwise you will miss the boat.”

Ben is concerned that many sheep and beef farmers don’t know whether they have drench resistance on their properties and may be using drenches that are not effective.

This can be determined very simply with a Faecal Egg Count Reduction Test and having an understanding of the resistance or susceptibility status of the worm population on an individual farm, will be central to developing a long-term strategy for the control of production-limiting internal parasites.

Ben believes genetics are another important tool in the long-term management of internal parasites and while many studs have been breeding resistance or resilience- or sometimes both- into their sheep, commercial farmers may not have been utilizing this genetic tool as much as they could.

“Genetics are going to be a huge part of the solution.”

He points out that it takes 10 years before genetic traits such as resistance and or resilience become firmly established in a ewe flock, so commercial farmers need to start exploring genetics long before they need it to manage internal parasites.

This means having a conversation with the stud breeder to ensure they are heading in the direction the commercial flock needs to go.

Ben says there is a significant difference between resistance and resilience, each with its advantages and disadvantages, but there are also stud breeders selecting for both traits.

Again, there are complexities about genetic selection for internal parasites and these are covered at Wormwise workshops.

Ben is one of several animal health experts who run Wormwise workshops throughout the country. Facilitated by B+LNZ, these workshops can be held upon request.

Wormwise is the product of an industry initiative to develop a national worm management strategy. Wormwise delivers this strategy by managing and integrating research work, education, communication and extension services for farmers, veterinarians, key influencers and retailers.

For more information about the management of internal parasites go to: