Friday, March 29, 2024

No silver bullet

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There is no single formula for deciding the best approach to worm control. The latest research into the production and cost benefits of pre-lamb ewe drenching has highlighted the complexity of drenching decisions. The Wairarapa trials – aiming to measure the benefits of various drench treatments in pregnant ewes – also reignited debate over the use of controlled release capsules and long-acting products.
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Trial results (see Country-Wide July 2015) showed variable benefits from drenching ewes pre-lamb. In some cases ewes treated with controlled release capsules were heavier and reared heavier lambs but not consistently. 

The research raised concerns about the role of routinely drenching pregnant adult ewes in accelerating drench resistance, especially with long-acting or controlled-release products. Vet and PGG Wrightson technical expert, animal health, Andrew Dowling hopes the study has given vets more information to take to farmers to discuss the suitability of using capsules and long-acting drenches.

“I hoped the study would give us more tools for decisions around whether or not you can make money out of capsules,” Dowling said.

“It doesn’t do that because there is no simple answer. The fact that they didn’t get a clear result tells us a lot, and it was a large and well-planned trial.”

Dowling said drench capsules are a large cost for farmers and most farmers don’t know if they make any money
from them.

“I think they get used too often as a prop – farmers are scared to stop using these products even though they have improved the feeding of their stock and we also know they’re very high-risk for developing resistance.”

His advice when making a decision on these products is to look at the animals that need it most – typically in-lamb ewe hoggets or two-tooths, whose immune systems are not fully developed. Dowling’s recommendations:

Look at the ewes’ body condition and perform a faecal egg count. Identifying low-body condition ewes early allows farmers to prioritise feeding and boost performance. Identify and rectify any mineral deficiencies.

Plan where these ewes will be lambing and use adult sheep or cattle to lower the worm challenge on these parts of the farm before lambing.

If you are using capsules or long-acting products it is important to leave some of the mob untreated for refugia to help slow the development of drench resistance. Dowling said to start small – about 10% – and gradually increase the size of the mob that is left untreated to find what best suits your farm.

A faecal egg count at docking will tell if a long-acting drench is not working (resistance) but a zero egg count does not guarantee it is working. An exit drench at weaning (usually triple combination) will remove worms that are resistant to the long-acting product used.

Dowling also advises that farmers using long-acting drenches do a faecal egg reduction test to ensure the products are working and not encouraging resistance.

Long-acting drenches can be a valuable tool when used wisely but are overused and farmers need to put more rigour into their decision making, Dowling said.

“We need to protect these products for the years to come and they are already showing signs of failing.”

Targeting treatment

Dr Abi Chase is technical product manager for Merial New Zealand, the company selling Bionic capsules. Bionic offers 100-day protection against all major parasites and is a popular pre-lamb tool for farmers.

Chase, a veterinary parasitologist, responded (Farmers Weekly July 20, 2015) to reports of the trial results, agreeing that farm management practices can have a significant effect on parasite challenge and the level of response to drench treatments.

She said removing worm challenges is likely to increase productivity in ewes. If controlled-release capsules are applied around lambing, improved ewe condition and lamb nutrition should be expected.

“The potential return on investment from capsules is mob-specific so their use should be based on a sound cost-benefit analysis which looks at productivity, management and financial factors.”

Chase’s recommendations are similar to those from animal health experts. She said to review each mob’s situation well before lambing and not to treat all ewes. Instead, target treatment for ewes that are most likely to provide a return on investment.

Chase stressed the importance of choosing the right product – based on management policies and drench resistance status – and monitoring drench performance.


Nature and nurture

Dave Robertson, a vet at the Veterinary Centre Oamaru, said the attention the Wairarapa trials have put on pre-lamb drenching is positive.

“We’ve always got to challenge what we’re doing,” Robertson said.

He was not surprised by the variable results.

“The sheep and parasite relationship is very complex. We discuss pre-lamb worm treatments on a farm-by-farm basis – what’s appropriate for one farm may not be for another.”

Robertson is comfortable with the strategic use of capsules. His field trial on pre-lamb drench strategies in 2008 showed a return on investment from long-acting drenches of $9 for each two-tooth ewe treated.

“The net return on investment might not be as high or as consistent in mixed-age ewes but for some farmers it gives them an insurance that ewes will hold up during spring and pastures will not be overly contaminated.”

He said sustainable drench use was important but resistance issues involved more than just the product being used.

“It’s the drench practices onfarm, how stock are moved around the farm and the level of refugia onfarm. You’ve got to find a refugia system that’s practical for each farm.”

Robertson has carried out drench efficacy tests on farms that consistently capsule ewes. Some have had resistance issues and others have not.

“The difference is the farm environment and the management practices that go along with using that drench.”

Before recommending what, if any product to use Robertson considers stock condition, productivity levels (how many scanned twins and triplets), feeding levels pre-lamb, how the ewes will be set stocked and the farmer’s priorities for the season.

He said capsules were popular in some extensive South Island farming systems where pasture quality or ewe condition cannot always be controlled.

“For a lot of high-country farmers long-acting drenches have really changed their animal health positively.”

North Island veterinarian Trevor Cook is treating the trial data with some caution because of the difficulty in getting clean data from such studies. The trial suggests a link between feeding levels and response to pre-lamb drench treatments but does not link the two clearly, he said.

Cook said it would be useful to measure the performance response for each hectare, rather than per head.

“How do we know the heavier weaning weights in ewes with capsules weren’t big singles?”

Cook has never been a big supporter of capsules because of sustainability issues around resistance and the fact any benefit is strongly related to the situation they
are used in.

Sheep under pressure are more likely to show a benefit from capsules or long-acting products.

“I see a place for them when heavily pregnant ewes are going to lamb under feed pressure. A two-tooth ewe will have lower immunity and be of higher risk of internal parasites limiting their performance.”

Cook is certainly not in favour of capsuling whole ewe flocks every year and said capsule use needs to be a well thought-out decision. “Ask yourself the question – are the ewes really at risk?” he said.

Despite the variable results, Richard Hilson of Vet Services Hawke’s Bay said the trial shows there is some benefit to capsule protection pre-lambing.

“The reality is that they’re available and we should use them carefully.”

Hilson said farmers treating entire mobs consistently should carefully consider their reasons for doing so.

“Having cleaner ewes is a poor excuse for mass medication – get a crutching gang in.”

Hilson said farmers need to better understand refugia – ask your vet what it means, why it is important and how to use it. If all the information around pre-lamb drenching sounds too complicated simply ask your vet to cast an eye over your ewes (do some condition scoring and faecal egg counts) before lambing to offer some advice.

  • Read more on capsules, long-acting drenches and resistance issues in the Country-Wide Sheep special out in October.

 

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