29-05-2025
Be alert to the risk of gut worms
HERD HEALTH SERIES: Maura Langan, Commercial and Technical Manager (Large Animal) at Norbrook.
Maura Langan, Norbrook Veterinary Advisor.
The warm, dry spell in March was welcomed by farmers and led to cattle being turned out earlier than usual.
While we have had a healthy spring, farmers will need to factor in the early exposure to worms and a longer grazing period when dosing their cattle.
Young calves are totally naive to parasites but will acquire some immunity as they are exposed to gut worms over time. As vets and farmers, we try to balance that exposure against the welfare and production losses associated with a significant worm burden.
As a result, we tend to group animals according to risk. In a seasonal calving system like Ireland, that tends to be first grazing season (FGS), second grazing season (SGS) and adult cattle.
Although there are around 20 types of gut worms that affect cattle, the two that are most economically important are Ostertagia and Cooperia. Over-wintered infective larvae are ingested soon after turnout and complete their lifecycle within the cattle before eggs are excreted back onto pasture.
On dairy farms where cattle have only been housed for a couple of months and there have been few sustained frosts, it is likely that a significant number of viable larvae will have survived.
Young FGS dairy calves are particularly vulnerable as they ingest more vegetation than suckler calves of the same age. Depending on the grazing pressure and level of contamination they may need anthelmintic treatment after only a few weeks.
Clinical infections of parasitic gastroenteritis are often associated with scour, but it is the suppression of appetite that occurs in both clinical and subclinical cases that causes reduced growth rate. Parasitic infections can also lead to other developmental and fertility issues such as a delay in puberty, reduced conception rates and increased calving intervals.
The decision when to dose and with what product, should be discussed with your vet. They will have a detailed knowledge of your farm, management system and its history. As well as being able to prescribe anthelmintics, they may undertake diagnostic tests such as faecal egg counts and recommend preventative grazing strategies.
For FGS dairy or dairy-to-beef cattle, a key consideration will be the persistency of the product used. Some products, such as Taurador Pour-On or the new Taurador Injection protect against re-infection for up to 6 weeks after treatment. On farms where it may be difficult to bring cattle in to treat more regularly, this could be an appropriate strategy. The need for fewer worm doses can save both time and money, especially on busy dairy farms.
Immunity to Ostertagia takes longer to build, so although SGS cattle may still need anthelmintic treatment, it may not be necessary until later into the summer. Products without persistency, such as Levacide Low Volume, may require more frequent retreatment but can be effective in allowing exposure to gut worms while checking the effects on production.
Of course, the Irish climate may still have surprises for us, as our recent spell of warm weather looks set to change. Temperature does play a part in the hatching and development of worm larvae within the dung pat, but moisture is also required.
In fact, rain plays an essential part in the distribution of larvae throughout the farm as faecal matter is through water flow and spread via transport hosts including cattle.
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