19th May 2021

Controlling Worms on Farms

Controlling Worms on Farms By Ally Anderson of Zoetis There has been a challenging start to the grazing season across the country with an unusually cold and dry April leading to poor grass growth in many regions. This is likely to have an impact on the parasites that we often expect to see at this time of year and emphasises the importance of monitoring flocks to make sure any treatments are given at the correct time. Nematodirus Lambs that are grazing fields that were grazed by lambs the previous year will be at risk of Nematodirosis – caused by the Nematodirus battus worm. We would usually expect Nematodirus to cause problems in lambs that are 6-12 weeks of age coinciding with when they are likely to have started eating decent quantities of grass. This year there has been less grass available, potentially leading to poor ewe milk production, with the knock-on effect that lambs may be grazing grass at a younger age and therefore at risk of worms earlier than usual. It is important to be aware of the potential risk of Nematodirus on farm as in the right conditions there can be a mass hatch of infective larvae from eggs on pasture, with lamb deaths the first sign of the problem. Information on the risk in your area can be found at the SCOPS Nematodirus Forecast (https://www.scops.org.uk/forecasts/nematodirus-forecast/) which can be used to help decide the optimum time for treatment. White drenches are a suitable treatment choice for Nematodirus, however it is important to check that there is not a mixed infection present that could require a different treatment. Stomach Worms Stomach worms can have a big impact on productivity and profitability of lambs at pasture if steps are not taken to control them. There are various species of worms that can affect grazing animals and they can cause poor carcase quality, decreased wool production and a reduction in growth rates which leads to delayed finishing times. It is important to have a worm control plan in place that will minimise the impact these parasites can have on the lambs. Good worm control is a balance between the level of challenge that would reduce productivity and the level required to enable the development of protective immunity in the lambs. Low levels of infective larval challenge have minor effects on growth rates but allow for the development of immunity. Larger challenges check growth and animals will not catch up to the cumulative growth rates that they would have achieved had the challenge been small. It is important to assess and reduce pasture risk – allow lambs to graze lower risk pastures such as hay and silage aftermaths or use mature ewes to ‘hoover’ larvae off infective pasture to keep larval exposure low. It is important that anthelmintics are only used when necessary to prevent the overuse of these products. As this spring has shown, there can be big variations in weather conditions and worm challenge across different seasons, so it is important not to dose based on the calendar. Growth rates and faecal egg counts can be used to assess whether treatment is needed. The Zoetis Parasite Watch scheme provides information on the worm challenge across the UK using data from 26 monitor farms. Farmers can access the latest Parasite Watch data by either signing up to receive updates or visiting the website www.parasitewatch.co.uk Anthelmintic Resistance Once a decision has been taken that treatment is needed, it is important that the correct product is chosen. Every time a product is used there is the opportunity for anthelmintic resistance to develop. If a treatment is given at the correct dose rate and a worm is able to survive, this is considered to be a resistant worm. This is a heritable process which means resistant worms are able to produce resistant offspring. When we refer to anthelmintic resistance we are referring to the worm population, rather than the lambs. The development of resistance to a specific active is a gradual process and when it begins to develop on farm, it may not be obvious that there is an issue. As worm resistance to a product increases and it becomes less than 50% effective, then it will be clear there is an issue. Unfortunately by this time it is too late to reverse the problem. To test how well a drench is working on your farm it is advisable to work with your animal health advisor. Drench checks can be performed which involve taking faecal samples from a group of animals on the day of treatment and then 7 or 14 days later depending on the active used. The results from this test can then be used to decide if further investigations are needed. If resistance to an active is found on farm, then it is important not to panic. There are many different ways of managing this issue and there is a lot of information and advice available for farmers to help with the situation. The best place to start is to find out what the situation is on your farm so that if there is a problem developing steps can be taken to help manage the issue. QMS have developed a booklet in collaboration with HCC and AHDB named ‘Worm Control in Sheep’. The publication can be viewed and downloaded from the publications section of the QMS website www.qmscotland.co.uk . A printed copy can be requested by emailing info@qmscotland.co.uk. View here - https://www.qmscotland.co.uk/worm-control-sheep-1

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