Further information

Environmental impacts of veterinary medicines

Antiparasitic drugs: treatment, modes of action, resistance and risks to the environment

To summarise the wealth of information available, only the most common endoparasites are examined in detail below.

An endoparasite infestation is primarily noticeable through symptoms such as diarrhoea, a rough coat, weight loss and loss of appetite. Gastrointestinal strongyles (MDS) (worms) occur in suckler cows and their calves when they are kept on pasture. The risk of infection is greatest for calves and young cattle during their first grazing season. The worms damage, for example, the mucous membranes in the gut. As a result, infected cattle can no longer utilise their feed adequately. Depending on the severity of the worm infestation and the state of the immune system, this can lead to significant weight loss and diarrhoea. Caution: Even without visible symptoms, a decline in performance can occur in second-calf heifers or cows; therefore, monitoring and prevention are important.

Over the course of the year, the larvae of the most significant member of the MDS – the brown stomach worm of grazing animals – are ingested by cattle after they are turned out to pasture in the spring. The larvae attach themselves to green plants, for example. The larvae ingested in the spring develop into adult worms within the cattle, which in turn can produce eggs. Cattle usually fall ill between mid- and late July, exhibiting diarrhoea, weight loss, a rough coat and excreting new worm eggs. After overwintering in cow dung on the pasture (where the egg develops into a larva), the cycle begins anew the following year. In addition to overwintering on the pasture, overwintering within the animal in the form of ‘hypobiosis’ is also possible, which can likewise pose a risk of infection or disease as early as late winter or early spring.

Unlike MDS larvae, lungworm larvae do not overwinter in the pasture but within their host, in older cattle and cows. As the immune system is not yet fully developed, calves on their first outing to pasture and young cattle are particularly at risk of infection, especially if they graze a pasture shortly after older cattle. In the case of lungworms, the next generation develops within approximately four weeks inside the host into the first larva, which is excreted in the faeces. After further development over about a week, the infectious larvae are dispersed across the pasture with the help of a fungus, but also through runoff during rain. Coughing is a sign of lungworms. This usually occurs in the second half of the grazing season and ranges from a mild cough to severe breathing difficulties. If symptoms appear in a herd, treatment must be carried out. If left untreated, severe infestation carries the risk of pneumonia.

The giant liver fluke migrates within the host’s body from the intestines to the liver and bile ducts. This can cause a drop in fattening performance or even fertility problems. Cattle ingest the liver fluke larvae with the grass. It takes six to eight weeks from ingestion to development into an adult fluke. A key factor in infestation is grazing cattle’s access to wetlands, the natural habitat of the intermediate host required by the liver fluke: the dwarf mud snail. Pasture management measures can be used for prevention here; see tips on pasture ^{management23, 24, 25}

Further information on various worm species and their life cycles

Decision-making guide: Grazing parasites: Gastrointestinal strongyles (MDS)

Pasture parasites in suckler cow husbandry

Decision aid for pasture parasites: lungworms

Controlling pasture parasites is a key component of pasture management. The growing development of resistance to anthelmintics makes successful treatment more difficult and highlights the importance of prevention through appropriate pasture management. Risk factors such as high stocking densities, permanent pastures, damp pastures or pastures used for young stock significantly increase the risk of infection and should be avoided.^1,2

Regular monitoring should be carried out to control worm infestation in animals. This is usually done by examining faecal samples from a section of the herd or from individual animals showing signs of infection, which are specifically selected. For gastrointestinal strongyles (MDS), this involves examining faecal samples from around 10–15 animals (regardless of herd size). The faecal samples from the animals tested should be sent to the laboratory within 48 hours. If the EPG (number of eggs per gram of fresh faeces) exceeds 100, the animals should be treated in consultation with the vet. A faecal examination is also necessary for the diagnosis and control of lungworm larvae. If an infection with liver flukes is suspected, faecal samples from individual groups of animals can be helpful for diagnosis. Egg excretion is highest in autumn/winter but not constant, so at least 5 animals from a group should be sampled.^{3, 13, 23}  

For suckler cow husbandry, the Thünen Institute’s decision tree can be used to determine, on a farm-by-farm basis, when faecal samples should be taken and when treatment should be discussed with the attending veterinarian. Calves and first-calf heifers are particularly at risk, especially upon their first contact with pasture forage. However, contact between grazing animals and parasites is also an important prerequisite for immunisation (preparation of the immune system) against endoparasites (e.g. MDS). Therefore, targeted deworming in line with the developmental stages of the endoparasites is a promising long-term measure to reduce the need for future deworming.^4,5

When keeping cattle on pasture, it is important to avoid additional stress (e.g. excessive heat or cold) in the event of a parasite infestation. Sick animals should not be left to overwinter on pasture, given the strain this places on their immune system.

Further information

Managing cold stress in suckler cows

Managing heat stress in suckler cows

An egg count reduction test can be carried out to monitor success. This is not considered a routine measure for cattle. If necessary, the farm’s attending vet can be consulted.

Further information

Sustainable parasite management

Sustainably controlling internal parasites in cattle through pasture management

Pasture parasites: Monitoring

• Faecal sample of fresh faeces (30–40 g)
• Packaging: break-proof and leak-proof, in accordance with (postal) transport regulations: Please contact your vet
• Until dispatch: store the sample in a cool place if possible; in summer months, have a cooling pack ready
• Choose a dispatch date so that the sample arrives at the laboratory as quickly as possible (preferably at the start of the week, not on Fridays or at the weekend)^17/18

Specific instructions for sample collection can be found on the respective websites of the relevant laboratories.

Further information

Taking faecal samples

• Key guidelines for parasite control in pasture-based husbandry: Use deworming products as required and follow the dosage instructions!
  • Please note: The weight of the animals must not be underestimated! This is a particular problem when all animals are given the same dose across the board
• To minimise adverse effects on nature and the environment, deworming agents should not be used prophylactically, but rather in a targeted manner and, where possible, on an individual animal basis. Important: in organic farming, the preventive use of antiparasitic agents is generally not permitted
• Treatment for gastrointestinal strongylid (MDS) infection:
  • Calves and young cattle in their first grazing season are most at risk
  • The need for deworming should be determined by faecal examination and the animals’ general condition. To prevent resistance, it is also advisable to leave animals that show no impairment in growth or weight gain untreated (further information on the refuge strategy)
• • If necessary, consult a vet to select a suitable antiparasitic agent
  • Various active ingredients and administration methods with differing durations of action are available (bolus, injection, liquid preparations)
• Treatment for lungworm infestation:
  • Antiparasitic drugs effective against MDS are also effective against lungworms
    • Please note: However, not all preparations combat both adult and juvenile stages of the parasite
  • If initial symptoms appear in a herd (usually in the second half of the grazing season), treatment should be carried out
• Treatment for liver fluke infection:
  • In winter, a preventive treatment can be carried out to avoid contamination on at-risk pastures the following spring
    • Important: At the start of the indoor period, only preparations that kill all stages of the liver fluke may be used 
    • These products may only be used on young cattle and heifers up to six weeks before calving
  • Towards the end of the indoor period, products may be used that kill^23,24,25 only adult liver flukes

In the event of an ectoparasite infestation, the entire herd is often affected. It is essential to closely observe all animals for signs of infestation. If skin changes caused by an infestation are visible, a skin scraping can be examined under a microscope to identify the specific type of mite. Lice and chiggers can be easily identified and distinguished with the naked eye. The burden on animals caused by flies in the pasture can be reduced using pyrethroid-containing fly ear tags/ear clips, garlic-containing mineral supplements, or, in the case of a severe infestation with other ectoparasites, infusions. In addition to treatment with insecticides, it is advisable to adjust the grazing schedule: for example, the animals can be allowed to graze only during the early, cooler hours of the day, or alternatively, grazing can be switched from daytime to night-time grazing. It should be noted here that whilst this is helpful for controlling pasture biting flies, midges are crepuscular and nocturnal. If necessary, there should be the option of bringing the animals indoors. In the event of a severe fly infestation on the pasture, potential breeding sites for the ectoparasites (e.g. damp areas around water troughs) on the pasture should also be dried out. To alleviate itching caused by an ectoparasite infestation, rubbing posts may be provided; however, these must be cleaned and disinfected after use by an infested herd and replaced if necessary to interrupt transmission routes. Particular caution is required with regard to tail mange (caused by biting mites): this mite can survive in the environment for 2–3 weeks and uses the cow brush to infest other animals. The same applies to lice and hair lice.

It is also important to ensure an adequate supply of trace elements for cattle, as trace elements play a significant role in building the immune system. A deficiency leads to increased susceptibility to infection; for example, inflammation and disease may occur more frequently in the event of a parasite infestation. Reduced performance and fertility problems may also result.^{5,8,9,10,12,15}

Further information

Not just a nuisance. Ectoparasites such as lice, chiggers, scabies mites and ticks not only cause cattle to suffer, but also result in economic losses that should not be underestimated

Cows, wasps, chickens – what can be done about flies?

Factsheet on parasites: Beef cattle rearing and young cattle rearing on pasture

Keep an eye on trace elements in pasture-based systems