Quarantine drenching with four unrelated drench actives followed by a strict quarantine protocol will help farmers minimise the risk of importing multi-drench resistant worms onto their property when buying in lambs.
Wormwise vets Ginny Dodunski and Mary Bowron says sheep farmers buying in lambs this autumn possibly already have some level of drench resistance on their farms, but they don’t need to make it worse by importing worms with even nastier genetics.
Sale yards lambs
The pair say lambs sold through saleyards are likely to have already had several combination drench treatments. Awanui Veterinary laboratory data from last season showed that 51% of farms tested had triple drench resistant Trichostronglyus . Given that farmers are unlikely to be able to get reliable information on the vendor’s drench resistance status, these are a ‘high risk’ class of stock for bringing resistance parasites onto a farm.
Private sale
Dodunski and Bowron recommend farmers buying lambs ask their vendor or agent for comprehensive drench testing data.
“If the drench data is available, does it look any good and do you understand it? Ideally, it should be checked by an expert in parasite management.”
They say while data from a Faecal Egg Count Reduction Test (FECRT) undertaken in January can look good, the pattern could have changed in the past few months.
“Get advice. If the vendor can’t give you comprehensive data that shows stable and high performance of routine combination drenches on their farm (and note that there are very few farms who can give you this information), then a proper quarantine protocol will be required.”
Treatment protocol
They say that due to the prevalence of triple drench resistance in New Zealand, reaching for a triple combination drench is not an effective quarantine drench. A ‘novel’ drench such as Startect® or Zolvix must, as a minimum, be part of a quarantine drench plan.
Dodunski and Bowron say there are an increasing (albeit small) number of farms that have diagnosed resistance to the ‘novel’ drenches Monepantel+Abamectin (Zolvix®) or Derquantel+Abamectin (Startect®). For this reason, the gold standard quarantine treatment is a combination of FOUR unrelated actives, one of which should be a novel drench.
“In practical terms this means a Zolvix® or Startect® administered at the same time as a BZ/Levamisole combination drench. These two drenches must not be mixed together as there may be issues with incompatibility that make the treatment ineffective. “
They say when two drench products are used at the same time, an extended meat withholding period (WHP) may apply.
“Speak to a veterinarian for guidance. A New Zealand residue study has shown that 28 days is a sufficient WHP for Zolvix® administered with a BZ/Levamisole drench.”
What next?
Dodunski and Bowron stress the need to properly manage the quarantine protocol.
“The drench doesn’t kill worm eggs, only adults and larvae. The eggs will continue to pass out of the lambs for a few days after the worms are dead and the bulk of these eggs are probably passed within the first 24 hours.” says Dodunski.
They say treated lambs need to be held in an area where these potentially drug-resistant eggs cannot develop into larvae.
“A bare yard (with water and good quality silage) is perfect, but not always practical. Use of a quarantine paddock needs to be managed very carefully. Farmers must be absolutely disciplined about other sheep not grazing this paddock and then spreading resistant worms that have developed from new arrivals.”
Newly arrived lambs should not stay in the quarantine paddock for longer than the time that the quarantine drug is active in their system, in case the new arrivals pick up others’ resistant larvae after the treatment wanes.
They say a practical compromise is to hold lambs in their quarantine area for 24 hours after treatment (after which time the bulk of the resistant eggs should have passed out), and then graze them on the most contaminated areas of the farm for at least a few days – any resistant eggs that pass out should be ‘diluted’ by the mixed worm population already present.
“If you’re an arable or maize farmer, you may only have new grass. But in this circumstance, the highly effective quarantine and clean high-quality feed should mean that no (or very little) further drenching of lambs is required. Look for other reasons for poor performance (and do some monitoring) before reaching for the drench gun again.”
Did it work?
In an ideal world, farmers would FEC sample the mob after 7-10 days to ensure the treatment had been successful. If were eggs present, Dodunski and Bowron urge farmers to contact their animal health advisor for advice on further treatment and management of the paddocks they’ve been grazing.
“Farmers will need to clean up those paddocks whilst ensuring the resistant worms don’t get spread further.”
Check out the Quarantine drenching page on the Knowledge Hub for information on quarantine at your fingertips.