Course: Winter Health | Last Updates: 12th October 2015
Treating calves against worms is vital in the run-up to winter housing, as they can weaken a calf’s ability to fend off other housing-related illness such as pneumonia. In some cases, youngstock mortality rates of up to 10% can occur thanks to worms. Incidences of liver fluke and lungworm are an inescapable part of cattle production, but with occurrences increasing in recent years it is worth talking to your vet now to plan a prevention and treatment strategy.
What are the most common parasites?
The main parasites associated with disease in calves are: Ostertagia ostertagi – a roundworm also known as the brown stomach worm, and Cooperia, which is very common in young cattle in the first grazing season. Cooperia is the main contributor to faecal worm egg counts.
Lungworm, or Dictyocaulus viviparus, is usually seen in first-year grazing season animals in summer or early autumn, although it has been increasingly reported in older animals over the past few years. Parasitic bronchitis, caused by lungworm, is now recognised as the commonest respiratory disease of adult cattle in the UK.
Disease due to liver fluke is caused by the Fasciola hepatica parasite. Over the past 10 years liver condemnations at abattoirs due to fluke have soared to about 20%, with even traditionally drier regions of the country now beginning to be affected.
How does infection occur?
Animals are infected by ingesting larvae on contaminated grass. With gastrointestinal worms, ingested larvae develop into adult worms inside cattle after three weeks, before going on to lay eggs in the intestine. The eggs are then passed out in faeces, and the cycle continues.
Adult lungworms produce eggs in the lungs which contain fully-developed larvae that hatch almost immediately. These migrate up the trachea, are swallowed and then pass out in faeces. Under optimal conditions, larvae can find their way to the grass and be ingested within five days. The larvae travel to the lungs via the bloodstream, where they break out of the capillaries into the lung about a week after infection. After a few days they moult and move up the bronchi to mature.
The life cycle of a liver fluke parasite involves a mud snail as an intermediate host and several free-living stages. The role of the snail, which prefers muddy, slightly acidic conditions, means the incidence of liver fluke is greater in wetter areas of the country.
Adult fluke lay eggs in the cow’s bile duct, which are passed out in faeces. At suitable temperatures a larva develops, hatches and actively seeks out a snail host, where it multiplies.
With the sail’s capacity to produce 100,000 offspring in three months, there is potential for large numbers of parasites on the pasture. Eventually the larvae emerge from the snail on to grass, where they can be eaten by grazing cattle. Once ingested they tunnel into the liver, causing considerable damage on their way to the bile ducts. Infection is evident, by production of fluke eggs, about 10-12 weeks after ingestion and the whole cycle takes up to 20 weeks.
What are the clinical signs?
All parasitic infections can result in poor weight gain and performance as well as hampering an animal’s ability to fight other illnesses. Roundworms typically affect young calves during their first grazing season, causing gastroenteritis, diarrhoea and weight loss.
Lungworms also tend to affect young cattle during their first grazing season, with infection characterised by bronchitis and pneumonia. Most animals recover slowly with treatment, but death can occur in some cases.
Liver fluke affects cattle in two stages: Immature fluke migrating through the liver can cause liver damage and haemorrhage, while heavy infections of adult fluke in the bile ducts feed on blood, resulting in anemia. Growth rates can fall by up to 20%, while milk yields can reduce by up to 8%.
How can you treat it?
There are a variety of worming products available for treatment and prevention of worms, which are available as injections, drenches, pour-ons or boluses.
Broad-spectrum anthelmintics are effective against a range of parasites, while narrow spectrum wormers are more targeted against fluke and some bloodsucking nematodes. Different products act against different life stages of worms and fluke, so it is important to work with your vet to develop a worming strategy.
Poor treatment techniques can lead to treatment failure, so it is important to make sure you know the weight of your animal in order to calculate the correct dosage. Under-dosing can lead to the worms evolving and adapting to its presence without being harmed.
If in doubt, dose for the heaviest animal in the herd, but remember to only dose when needed and rotate the type of wormer used to avoid resistance build-up. The introduction of longer-lasting wormers, which offers protection against reinfection for five or six weeks, can be particularly useful for youngstock health if used several weeks before housing for the winter.
Treating a calf before it is moved means it is able to cough up dead worms from its lungs at an earlier stage. This gives cattle the best chance for their lungs to be repaired before the stresses of housing, which can lead to illnesses such as pneumonia.
Early worm treatment is also more cost-effective, as the calves are lighter and do not require as much wormer as they would do at housing, while it is also been found to help boost growth rates by up to 0.15kg a head each day, resulting in an additional 5.25kg over the period.
How can you prevent infection in the first place?
Worms are an inescapable part of livestock production, but there are measures to minimise their impact.
Following repeated exposure, cattle become immune to worms over one or two seasons, however farmers with a major lungworm problem should consider vaccinating, which can reduce the need for routine worming. Producers often rely too heavily on routine dosing, which can lead to resistance build-up and make long-term worm control difficult.
Experience in the sheep sector has shown than over-reliance on anthelmintics can result in the parasites becoming resistant to wormer doses that are normally lethal. Instead, farmers should adopt a more strategic approach, including rotation of pasture and use of faecal egg counts to enable them to target wormers more effectively and to cut costs.
As youngstock are most at risk of worms, try to graze them on low-risk pasture such as new leys or fields previously grazed by adult cattle or sheep. Also use older cattle to clean up the larvae present in high-risk fields, as older cattle have built up immunity. Carrying out regular faecal egg counts when planning to worm will help identify the need for it, while occasionally repeating it afterwards will help test the efficacy of the wormer used.
Tests to identify the dominant parasite type can also be carried out to ensure targeted treatment. In the case of liver fluke, it might be worth thinking about draining wet pastures to reduce snail numbers. Eliminating poached land around water troughs and gateways and fencing-off marshy areas can also help.
- Plan a control strategy with your vet or adviser
- Use wormers only when necessary and reduce dependency on them by adopting pasture management strategies
- Administer wormers effectively and according to manufacturer’s instructions
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