Spring Pastures: What to consider before letting your animals out to pasture

With lambing season upon us, there are many things to consider when grazing animals. Many cattle herds and sheep flocks are housed indoors over the winter months for various reasons. I’m sure they wouldn’t be too fond of the recent snow flurries that we’ve had! Indoor housing during the winter months provides protection from the elements and cold conditions, as well as conservation of energy that would have been spent keeping warm – meaning the energy can be better put into lambing, lactating or putting on weight. Additionally to these, it also allows time for the animals to be kept off the land to allow it to recover and to avoid poaching. It also permits treatment for parasites, away from infective larvae.

Whatever the reason for housing animals indoors over the winter, putting them back out to pasture in spring must be partnered with a good understanding of the risks of infection that come with the warmer weather, after wet and cold conditions. Some of the most prevalent parasites during the spring time are discussed below.


Nematodirus is a roundworm found on pasture in large numbers during the spring – the so-called spring flush. This worm typically presents in young lambs so potentially one to watch out for if lambing or letting out young lambs onto pasture. The worm begins to hatch as L3 larvae from eggs once the temperature reaches around 10°C after a long period of colder weather – perfect spring conditions! For more on nematodirosis, check out this article. A local risk forecast is also produced by NADIS, so make sure to take a look.

Liver fluke

Liver fluke (Fasciola hepatica) infects both cattle and sheep. To become infective, liver fluke eggs must hatch on pasture and infect the snail Galba truncatula. For this to occur the conditions must be wet and muddy, and between 7-10 °C – perfect spring weather. Immature liver fluke develop in the snail and emerge as cercariae onto pasture where they attach to  grass ready for livestock to consume whilst grazing. If clinical disease presents, this is likely to be seen  from August onwards, due to time needed for migration of fluke through the liver and development into adults. The exception to this is when large numbers of immature fluke cause disease as they migrate through the animal’s liver on route to the bile duct home of the adult fluke. Animals infected with fluke can be pre-disposed to develop Black Disease. For more information on liver fluke, look at our previous article.


Last year, we wrote an informative article about Lungworm in sheep and cattle. This worm is a nematode that affects many host species, with each host having its own species of lungworm. For instance the lungworm that infects cattle is Dictyocaulus viviparus whereas in sheep it is  Dictyocaulus filaria. The typical tell-tale sign for a lungworm infection is a dry cough, known as a ‘husk’. Severe cases can cause weight loss and breathing problems. Managing lungworm in cattle can involve vaccination, monitoring faeces for larvae and treatment where necessary. There is no vaccine for lungworm in sheep so monitoring faeces for larvae and treatment, alongside pasture management are the control options.  

How to combat risk of infection when putting animals out to pasture

There are many ways to reduce risk of infection and impact of infection when animals go out to pasture.

Testing and treatment

Get a Pasture Larval Count Test. Do you want to see if your pastures are clean as well as your animals? We can do this for you! This test will help to manage your pasture and so prevent your animals accumulating parasites. This can be a one-off sample or we can monitor at intervals through the grazing season. Price (including VAT): £120.00 per test for 1-4 samples, £110.00 per test for 5+ samples. Please use this form: Pasture Larval Count Submission Form

Get regular Faecal Egg Counts. This will allow you to monitor the infection levels within your animals, and can be used as a guide on when to treat (and which animals to treat). This can be done for individual animals, potentially young lambs or calves, or for the flock or herd as a whole to check their infection status. There is no point in giving a wormer if your levels are already low! Check out our guide to FECs or if you would like to order one, click here.

Faecal Egg Count reduction: Samples can be taken before or after treatment with a wormer, to assess its effectiveness. This test will tell you how much the parasite burden has been reduced, so that you can decide next steps and whether the results are sufficient.

Anthelmintics or Wormers. Obviously, these cannot be relied upon as a first go – to and should be used as part of a well thought through management strategy . Correct use of wormers is essential, for example, for preventing increased anthelmintic resistance, so please always consult your vet for advice. See our article on when you should use a wormer here.

We also recommend a lungworm test in animals observed coughing and a Liver & Rumen Fluke test. These eggs cannot be counted accurately in a FEC and so a different test must be conducted. These tests can be really beneficial in spotting infected animals that have no signs and therefore enable prompt treatment.


Prevention by grazing pastures used by different species in the previous grazing season

Try to graze both cattle and sheep together to reduce the number of hosts available for species specific parasites. Alternatively, a rotation system of one then the other during the season may be more practical.

Once weaned, move young lambs to alternative pastures which have been less heavily grazed, to lower contamination.

Keep animals grouped by age at turnout as this is better for a composite FEC (taking about ten samples and combining them into one) and worming treatments.

Ewes post-weaning can be put onto contaminated pastures to reduce infectivity. They will act as hoovers, consuming large numbers of larvae without shedding large numbers of eggs back onto pasture.

Good nutrition is a key component in animals maintain their health when infected with high parasite burdens. This should help them to withstand better the stress from challenge of parasites. Ewes can be fed feed with high undegradable protein levels to reduce worm egg output, and creep feeding lambs can be provided with additional nutritional support, thus reducing early grass intake and thus  delaying exposure to any larvae on the pasture.

To conclude, by considering all of these factors, it is pertinent to have a well thought through management plan to reduce risk of infection to naïve and mature animals.