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

With lambing season upon us, there are many things to consider when grazing animals on spring pasture. Many cattle herds and sheep flocks are housed indoors over the winter months for various reasons. 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, during this time, the land can recover from grazing. 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. The following are some of the most prevalent parasites of springtime.


Nematodirus battus is a roundworm found on pasture in large numbers during the spring – the so-called spring flush. This worm typically presents in young lambs. Consequently, it’s one to watch out for if lambing or letting young lambs out to 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 – classic spring conditions! For more on nematodirosis, the disease caused by the worm, check out this article. NADIS produce a local risk forecast, 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. This only happens when the conditions are wet and muddy, and between 7-10 °C. Immature liver fluke develop in the snail and emerge as cercariae onto pasture where they attach onto grass ready for livestock to consume whilst grazing. Clinical disease tends 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. Black Disease is more common in infected animals. For more information on liver fluke, check out our previous article.


Last year, we wrote an informative article about lungworm in sheep and cattle. These worms are nematodes that affect 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. A dry cough, known as a ‘husk’ is the typical tell-tale sign of a lungworm infection. 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. The most straightforward methods are through testing for and treating the infections as they arise. Changing the way you manage your flocks or herds can also have major implications on infection rates. This generally requires a bit more planning and time to implement, but the rewards from having healthy livestock are huge.


Before you put your animals out, you can 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 throughout the grazing season. If this sounds like something you might like, please use this form.

Get regular Faecal Egg Counts. This will allow you to monitor the infection levels within your animals, and decide when 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.

Similarly, you can get a Faecal Egg Count reduction. You can take samples 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.

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.


Finally, you can treat animals with anthelmintics or wormers. These cannot be relied upon as a first go and should be used as part of a well thought through management strategy. It is essential to always use wormers properly. If not, you can increase the risk of anthelmintic resistance, and might not treat infections, so please always consult your vet for advice. See our article on when you should use a wormer here.


Animals out to pasture can pick up parasites.
Animals out to pasture can pick up parasites.

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. Similarly, rotating different species between years can reduce the spread of specific parasites.

Ewes post-weaning can reduce infectivity when put onto contaminated pastures. They will act as hoovers, consuming large numbers of larvae without shedding large numbers of eggs back onto pasture. Conversely, weaned young lambs act as contaminators of pastures. As such, you should move them to clean and uncontaminated pasture to help them keep their parasite loads down.

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

By considering all of these factors, the best practice is to have a well thought through management plan to reduce risk of infection to naïve and mature animals.