Figure 1: Temperature and rainfall by region for previous months. Egg count data shows the most recent counts for roundworms in sheep at each location between the sample dates stated.
November started out mild, turning colder with sleet and snow in many areas before becoming milder with wet spells towards the end of the month.
The provisional UK mean temperature for November was 5.3oC, 0.9oC below the long-term national average (1981-2010). Regionally, below average temperatures were observed across all regions of the UK both in November and for the preceding 3 months (September – November). UK mean rainfall was 97% of the long-term average, although this varied between regions, with above average rainfall generally in the east and further south, particularly the midlands and north-east of England, and below average rainfall further north and west both in November and for the preceding 3 months.
Winter provides a good opportunity to review and plan on-farm parasite control strategies ahead of coming grazing season. Preparation will help you to develop a robust yet practical programme to reduce disease burdens, costs and selection for anthelmintic resistance. Please speak to your vet or SQP about devising a parasite control plan to work for your farm. More information on sustainable parasite control is sheep and cattle can be found on the “SCOPS” and “COWS” websites, and cattle and sheep-specific parasite control planners are available through NADIS (Figure 2), which can help devise and visualise your plan for the coming year. Important issues to bear in mind include:
Figure 2: Cattle and sheep specific parasite control planners are available through NADIS and can help develop a sustainable, practical on-farm strategy.
The liver fluke forecast for autumn 2019 predicted high risk in Scotland, northwest England & north Wales, moderate risk in Northern Ireland and low risk everywhere else (Figure 3).
Figure 3: 2019 UK autumn fluke risk forecast by region.
It is therefore advised that farmers with livestock still grazing in high and medium risk regions are vigilant for signs of disease, as well as farms in other areas with either a history of liver fluke, or permanently wet pastures. It is also important to be on the lookout for chronic infection at this time of year. Chronically infected animals may show no obvious signs of disease, but can have significant reductions in productivity (Figure 4). Furthermore, chronically infected sheep and cattle can remain infected for months or even years if untreated, meaning housed animals may still be affected. Such animals can also be an important source of pasture contamination in the coming season. If in doubt, please seek veterinary advice.
Figure 4: Chronic fluke infection in sheep caused by adult flukes living in the bile ducts. Such animals may show no obvious signs of disease so it is important to check for infection through diagnostic testing.
Advised actions include:
Figure 5: Chronic fluke infection can be identified through egg sedimentation using either individual or pooled faecal samples.
Where fluke infection is identified:
The dropping temperature observed in previous months mean larval development on pastures is likely to have stopped at this time. However, colder weather can increase larval survival over winter, meaning previously infective pasture are likely to remain so into the following season. In particular, Trichostrongylus species can continue to be a risk in store and replacement lambs and, sometimes, yearlings at pasture over the winter (Figure 6). It is therefore important to maintain vigilance for signs of disease in at risk animals grazing potentially contaminated pastures. Egg count data from the Parasite Watch from September to November 2019 shows moderate to high egg counts on a number of farms across Great Britain (Figure 1).
It is also important at this time of year to consider encystment and the arrested development of roundworm infections in yearling lambs. Animals carrying high levels of encysted larval infections are potentially at risk of scours similar to type-2 ostertagiosis in cattle, and these populations can also be an important source of early pasture contamination in the next grazing season. Since animals with encysted larval infections can be egg count negative, it is important to consider at-risk animals based on previous grazing history, treatments and levels of infection observed towards the end of grazing. If indicated, a number of anthelmintics carry a licence of efficacy against arrested larval stages. For more information on anthelmintic selection and treatment options please speak to your vet or SQP.
Figure 6: Trichostrongylosis is a common problem in store and replacement lambs in the autumn and winter months
Advised actions include:
Scab (mite) and louse infestations can become a significant problem in sheep flocks housed over the autumn and winter months, typically from September-April. Whilst the signs of scab and louse infestations are similar, treatment options may differ considerably since scab mites live on the skin, whilst lice reside within the fleece. This makes diagnosis an important first step towards treatment.
Sheep scab is caused by psoroptic mites (Psoroptes ovis). Infestations cause loss of condition, secondary skin infections and potentially death if not treated. Signs include severe itching, wool loss, restlessness, biting and scratching of affected areas and weight loss or reduced weight gain. When examined, the fleece may be wet, sticky and yellow due to serum discharge and the skin may become thickened and corrugated (Figure 7). Studies show scab mites can remain infective in the environment for up to 17 days. Consequently, fields, sheds and pens where infected sheep have been kept and handled should be considered a potential source of infection to other sheep during this period.
Louse infestations in the UK are mainly caused by chewing lice (e.g. Bovicola ovis) and may present in a similar, but less severe way to scab. Thin sheep tend to be most greatly affected, with widespread louse infestations often indicative of another underlying problem within the flock.
Figure 7: A severe case of sheep scab characterised by wool loss, serous exudate and thickening of the skin.
To reach a diagnosis:
Figure 8: Psoroptic mites (left) can be identified from skin scrapings, whilst louse infestations can be confirmed in affected fleece (right). Photos courtesy of Dr Joseph Angell.
Where treatment is required:
For growing cattle housed after their first or second season, treatment with a product containing either a 3-ML or 1-BZ anthelmintic is recommended as these are effective against encysted larval infections which may have been acquired in the latter stages of the grazing season. If untreated, heavy burdens of encysted larvae can cause type-2 ostertagiosis due to triggered mass emergence in late winter/ early spring (Figure 9). Encysted larval Ostertagia infections cannot be assessed by worm egg count.
Figure 9: Type-2 ostertagiosis is a potentially serious disease that occurs in housed young stock in the late winter early spring. It is caused by triggered mass emergence of encysted larval infections acquired at the end of the previous grazing season. It is important to consider at-risk animals at this time and treat appropriately to avoid clinical disease.
Louse and mite infestations in cattle are not uncommon during winter housing (Figure 10). Generally low level infections are not of major concern, but heavy louse infestations may indicate an underlying management or health issue and, where sucking lice are present, may cause anaemia compounding existing problems.
A range of pour-on and spot-on synthetic pyrethroid products are available with efficacy against lice, whilst group 3-ML pour-on worming preparations are also effective, and injectible group 3-ML preparations are effective against sucking lice.
A relatively small number of injectible and pour-on group 3-ML based products are available in cattle against mange mites, with some and pour-on synthetic pyrethroids preparations also effective. Where mange infestations are a cause for concern, please seek veterinary advice concerning further diagnosis, as the type of mite causing disease will help to inform treatment choice. Psoroptic mange in particular can cause severe disease (Figure 10) and in outbreaks treatment is usually necessary for all in-contact animals to achieve elimination.
Where treatment of ectoparasites is indicated, it is advisable to follow up with further examination and diagnostic testing. Resistance to synthetic pyrethroids has been identified in lice, whilst treatment of psoroptic mange with group 3-MLs can produce varied results often requiring multiple treatments. It is also important to note that scab mites can live in the environment for 2-3 weeks, meaning good disinfection and biosecurity measures are important for control. For more information on ectoparasite control in cattle please speak to your vet or SQP, and see the “COWS” guidelines.
Figure 10: Ectoparasites (louse and mite infestations) in housed cattle usually produce only mild, self-resolving signs (top). However, some parasites and circumstances, such as psoroptic mange (bottom) can lead to more severe disease and the need for appropriate treatment informed by diagnosis.
UK researchers are currently involved in a Europe-wide study looking at usage of dewormers in cattle and sheep. If you are interested in helping, please consider completing their questionnaire by following the appropriate link:
Sheep farmers, please click HERE
Dairy farmers, please click HERE
(English and Welsh language versions available)
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