Worm control measures need to protect the long-term impact of drugs available to sheep farmers


Tom Coll

Participants in Knowledge Transfer Groups for the sheep sector are required to complete an Animal Health and Management measure with a vet as part of an annual Farm Improvement Plan.

This involves one-to-one, on-farm consultation between the vet and farmer on topics such as flock health and production, parasite control, lameness and biosecurity.

Leitrim sheep farmer Clifford Richardson met up with his local vet Finbarr Kiernan, who is based in the Farm Vet Clinic in Cavan, to draw up a flock health plan for his farm.

Previously we discussed the production-related diseases and management practices to be adopted on the farm. This article will concentrate on parasite control, lameness and biosecurity issues specific to Clifford's flock.

Worm control is complex and farm-specific - and it's not just about killing the worms that are affecting the lambs.

It's also about ensuring the effective longevity of the anthelmintic drugs available to sheep farmers.

Finbarr's advice to Clifford was based on targeted treatments only when required and taking steps to prolong the efficacy of the drugs against the population of worms that exist on the farm.

The first dose that the lambs received was for Nematodirus, and the timing of the dose was based on the Nematodirus forecast released by the Department of Agriculture.

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Subsequent dosing was based on faecal sampling taken from lambs in the field every two weeks from June to September.

Eight samples were taken in total at a cost of around €18/composite sample. This enabled Clifford to make the correct decisions on when to dose and test the efficacy of the dose given. Taking 10 individual samples from 10 lambs in the field takes about 30 minutes.

From the results of the samples, Finbarr was able to tell Clifford when he needed to dose and which product to use.

Finbarr recommended that for the second dose Clifford use a moxidectin-based product, followed by Zolvix or Startect when the count was high enough post-weaning as a third dose.

The next dose involved sequential dosing. This required the use of three wormers given on the same day but not mixed by the farmer prior to administration.

A white (benzimidazole), a yellow (Levamisole) and a clear (ivermectin) can all be given at the one time.

This will enhance the long-term efficacy of each individual anthelmintic used on the farm.

Hoggets that lambed for the first time and hogget rams received similar dosing treatments as lambs.

This year Clifford faecal- sampled his lambs from May to mid-July, leaving a two-week interval between sampling.

The sampling results are outlined in the table below.

Lambs were dosed with a white wormer when the egg count reached 400 eggs/gm.

The subsequent sample taken 14 days after dosing indicates that the drug was somewhat effective in controlling strongyles on the farm, having reduced the count to 50 eggs/gm.

Finbarr's advice is to build up a profile of what is happening on the farm by sampling every 14 days.

In hindsight Clifford could have delayed drenching until the next sample was taken at the end of June.

Finbarr stresses the need for frequent sampling to avoid leaving very high egg counts on lambs untreated or treated with a product which has little control over the population of worms on the farm.

The relatively low worm burdens on the Richardson farm could be associated with the low stocking rate on the farm up until now.

However, as stocking rate increases, the need for the strategic dosing plan as discussed with Finbarr will be vitally important in order to prolong the efficacy of the anthelmintics used on the farm.

Finbarr also addressed the Fluke issue and advised the annual rotation of the active ingredient of various drenches effective against immature and adult fluke. The use of faecal sampling to test their efficacy would also be recommended.

Finbarr went on to assess the level of lameness that existed within the flock on the day of the visit. The incidence was low at 2pc in the ewes and 3.3pc in the lambs; all rams were clear of lameness.

Lameness in the flock was due to scald and foot rot. Finbarr recommends a combination of routine foot bathing for scald, and early intervention with antibiotics where foot rot has been detected.

He also stressed the need to cull repeat offenders or ewes that do not respond to treatment, as they are a constant source of infection for the remainder of the flock.

Biosecurity begins with dosing all new arrivals

WHEN sheep are bought in, they may be carrying resist­ant worms.

Vet Finbarr Kiernan says all bought in sheep should be treated with an abamectin and derquantel combination product (eg, 5-SI Startect) or with a moxidectin (3-ML) in­jection and a 4-AD monepantel drench (eg, Zolvix) which will kill both scab mites and resistant worms.

Each drug should be delivered separately; mixing of drenches on farm should never be carried out.

After dosing, sheep should be held in a yard for a min­imum of 24 hours (preferably 48 hours) with free access to water and food so that any eggs that may have survived treatment will have been passed out.

All faeces deposited while isolated should be carefully disposed of in a manner that ensures that sheep will not be exposed to it again — for example, do not spread on pasture where sheep will subsequently graze.

Sheep should subsequently be turned out to a field that has been grazed by the home flock and contains a parasite challenge, from which they should and remain isolated from the home flock for three to four weeks.

Clifford and Finbarr have decided to draw a line in the sand as far as purchasing females onto the farm. From now on, the only breeding sheep entering the farm will be rams.

They will be dosed as per protocol already mentioned and also be dosed with a closantel-based product for ma­ture and immature fluke which will also cover haemon­chus.

In the past, female replacements have been purchased from a small number of flocks where Clifford investigat­ed the flock history.

Operating a closed flock with the exception of pur­chased rams will significantly reduce the risk of introducing abortion-causing agents such as EAE into the flock.

Tom Coll is a Teagasc business and technology advisor based in Mohill, Co Leitrim

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