Expert advice on keeping parasites under control

By James Adams, Hook Norton Vets, Banbury, Oxfordshire

Parasites are costly to farmers in that they increase the input needed, both in time and money, and can significantly reduce a farm’s output when not properly controlled.

The effects range from decreased milk production, poor fertility and poor weight gain, to the sudden death of livestock.

Wet and mild seasons, rising stocking densities and increasing resistance to anthelmintics have made farmers more aware of the problems parasites present.

Various drenches, pour-ons and injections are the obvious solution, but taking a preventative rather than a curative approach may help save the pennies, with no adverse effects on the cattle.

The three types of parasites that clients predominantly ask me about are:

Stomach and intestinal worms

Intestinal and stomach worm eggs are excreted in cattle faeces. Eggs then develop into larvae while in the cowpat and migrate on to the grass, ready to be ingested.

Sometimes this process may stop due to a cold winter, and then re-start in the spring, when larvae still present a danger. Clinical signs include watery diarrhoea, leading to significant weight loss.

Most cases are seen in late summer when the worm burden is high, but farmers must be aware of spring cases due to the hibernation of the larvae.

Diagnosis of a problem is primarily done by faecal egg counts (FEC). At least 10 samples of fresh faeces are needed for your vet to have an accurate picture of the problem.

Do this every three months, or more frequently when clinical signs indicate there may be a problem.

Ideally, cattle should be kept off pasture for the following 48 hours so all worms can be excreted. After the two days have elapsed, place cattle on a pasture with a low-mid worm burden.

Re-test the FEC in 14 days. If there are still eggs, the worry would be that there is some resistance – discuss with your vet.

Double check your dosing volume and technique were correct. Re-check FEC. again 14 days later. Once the egg count is nil, move the animals to another pasture.


Lungworm larvae are ingested from the pasture having been excreted in faeces. Worms migrate into the lungs where they cause clinical signs such as coughing. Light infections in a dairy herd can decrease milk-yield.

Your vet will be able to diagnose the problem for you when you submit at least 10 faecal samples.

Husk is predominantly seen from July to September when pasture burden is at its greatest. Generally, lower levels in spring mean immunity is induced in cattle, but this is by no means a certainty.

Immunity to lungworm is induced within two to three weeks of infection and can also be introduced by vaccinating animals prior to turnout.

Immunity against both non-resistant intestinal worms and lungworms can be induced by grazing on pastures with low -mid level risks. This can be done by a variety of methods:

Graze cattle with sheep, which helps to decrease the stocking density and thus the worm burden

Graze previously unexposed beasts with older immune cattle, which will excrete eggs from non-resistant worms

Don’t worm the strongest beasts in the group, who will excrete a low number of eggs


Once ingested, fluke migrate to the liver where the damage they cause reduces the function of the organ. Mild forms are seen as poorer milk production and fertility.

Chronic disease causes weight loss, reduced appetite, and susceptibility to other diseases.

Fluke is dependant on wet and warm environments, hence why farmers have had greater problems with it over the past few years.

Most infection is seen from July until October but a warm summer can reduce this time-frame. Fluke can hibernate over winter and be ingested in the spring at turnout.

Diagnosis can be made by examining faeces, taking bloods or doing a bulk milk test.

Treatment includes anthelmintics that solely treat mature fluke while cattle are housed, or both immature and mature fluke when cattle are at grass. This may need to be repeated every six weeks according to the problem.

When you intend moving cattle after treatment, allow three weeks for the dead fluke to be excreted before putting on a new pasture.

Prevention is possible by keeping cattle off wet, boggy ground with drainage being the ultimate solution.

Solutions to parasite problems have to be practical and a plan of attack should be devised with the help of your vet. By constantly monitoring egg numbers, you can have a good idea of the challenges your cattle face and may be able to worm less – this represents a great saving in time and money.