Worm resistance worries in flocks
Anthelmintic resistance is a common problem on sheep farms, but few producers actually realise they have a problem until it gets completely out of control.
Leanne Kneebone, who keeps about 500 ewes with her parents at Turchington Farm, Lifton, Devon, never had an issue with wormer resistance, until she lost three healthy lambs in one weekend early this year.
“They were big strong lambs, so we immediately knew something was up,” she says. Having just become involved with the Healthy Livestock Initiative via Duchy College, she carried out a faecal egg count and discovered extremely high levels of coccidiosis, nematodirus and trichostrongyle.
“We hadn’t had a problem until then, which suggests the warm winter led to a higher worm burden on the pasture this spring.” She drenched the lambs with a white drench, but three weeks later lost another three lambs to coccidiosis.
“It got to the point where we were worming every three weeks just to keep on top of it. The lambs just weren’t building up any immunity – I think the burden was just too much for them,” says Miss Kneebone.
As part of the Healthy Livestock Initiative, Miss Kneebone carried out a trial to identify potential anthelmintic resistant strains present on the farm. One group of lambs born in late February and early March was treated as a control and not given any drench at all. Another group was treated with white drench, a third with clear drench and a fourth with yellow drench, with faecal egg counts taken before and after treatment to identify the efficacy of each treatment.
“The control group started out with a nematodirus egg count of 400, which increased to 1,600 after nine days, while ostertagia counts increased from zero to 600,” says Miss Kneebone. The yellow and clear drenches were 100% effective, but the white drench, while effective on most worm species, only killed 67% of the trichostrongyle worms.
As a result, Miss Kneebone’s vet advised her not to use white drench for worm control, instead alternating between clear and yellow drenches. “Before, although we had a closed ewe flock, we never quarantined the rams,” she says. “It wouldn’t surprise me if they brought some resistant worms in with them. We were also drenching our ewes twice a year, and drenched the lambs religiously every four or five weeks, which has probably led to a build-up of resistance.”
Now, the family only drench the ewes once a year, just before lambing when their immune systems may be compromised. “Having had a closed flock of Suffolk x Texel ewes for 10 years, we recently brought in some Mule ewes,” says Miss Kneebone. “As part of our flock health plan we made sure we quarantined them properly to reduce the chance of importing resistant worms.”
She now carries out regular faecal egg counts before administering any drench to the lambs. “I only treat the ones that look a bit mucky or aren’t doing very well, and if they’re part of a small group I will weigh them to make sure the dosage is correct. If it’s a larger group I will weigh the heaviest and treat to that level.”
After worming, Miss Kneebone turns the sheep back out on to contaminated pasture, to ensure competition against any remaining resistant worms. “We haven’t re-seeded for a very long time, so most of our pasture is probably classified as dirty – that may be another reason why the worm burden has been so high this year.”
Despite this year’s problems, she has cut the number of treatments from seven to six, saving 6p a sheep, as well as reducing labour. “It’s been a particularly bad year for worms because it’s been so wet; hopefully we’ll have a really cold winter and dry spring to help kill them off a bit. Next year we should be able to make greater savings as a result of faecal egg counting, and hopefully the lambs will finish more quickly now we’ve identified and addressed worm resistance.”
About the Healthy Livestock Project
The Healthy Livestock project is a Rural Development Programme funded initiative, led by the Rural Business School at Duchy College. It aims to demonstrate how improved animal health can boost production and profitability across livestock species.
The sheep strand involves 18 focus farms in the South West, highlighting key topics like lameness, nutrition, breeding and parasite control. Sheep farmers can receive subsidised sessions with their vet to identify their own farm’s anthelmintic resistance status and create a parasite control strategy.
Find out more about worms in your flock and test your knowledge with Farmers Weekly’s new look academy website
A wealth of flock health information is also available on our interactive flock focus page