Figure 1: Egg count data shows the most recent counts for roundworms in sheep at each location between the sample dates stated.
May began with showery periods, frosts and wintry conditions in northern and eastern regions giving way to warmer, sunny weather for most of the month, with generally cooler changeable conditions towards the end of the month and some warm weather in the south and east.
The provisional UK mean temperature in May was 10oC, 0.3oC below the 1981-2010 long-term average. Regionally, mean temperatures were at, or slightly below the monthly average. However, the regional average for the previous 3 months (March-May) was still above average across all regions.
Rainfall was 93% of the long-term monthly average for May. Regionally this varied, with very dry conditions observed in Wales and southern England, and above average rainfall in north-east Scotland.
PGE is caused by roundworms present within the digestive tract. Heavy worm burdens can cause serious disease in lambs, with signs including loss of appetite, diarrhoea, dehydration, weight loss and death in heavy infections. Lower levels of infection may have no obvious signs, but can still impact lamb performance, particularly weight gain.
Eggs shed in the faeces of already infected individuals and develop into infective stage larvae which are then ingested through grazing (Figure 2). Early in the grazing season, pregnant or recently lambed ewes are an important source of pasture contamination due to the increased egg output associated with the peri-parturient rise. These larval burdens then continue to accumulate on pastures where ewes and their lambs continue to graze as the season progresses.
Figure 2: Pasture contamination results from the development of eggs passed in faeces to infective stage larvae. Without appropriate control, large numbers of eggs and warmer temperatures later in the season can lead to high levels of pasture contamination and disease.
Weaning lambs are at greatest risk from PGE during the summer months due to the increased levels of pasture contamination combined with their increasing grazing activity, and since they have yet to develop a protective immunity.
Temperature plays an important role in development and survival of eggs and larvae at pasture, with faster rates of development at higher temperatures. The above average temperatures observed over the preceding 3 months (March – May) could therefore increase the level of pasture contamination expected at this time of year. Wet periods of weather may also help to liberate infective larvae onto pasture from faeces in relatively large numbers. Egg count data from Parasite Watch show medium and high egg counts observed in groups of sheep across Great Britain between April and May (Figure 1).
Advised actions include:
Haemonchus contortus or the barber’s pole worm is another type of PGE-causing roundworm. Unlike other PGE-causing roundworms, Haemonchus feeds on blood. A single worm may consume up to 0.05ml of blood per day, meaning in heavy infections large volumes of blood loss can occur rapidly. Consequently, whilst infection in the UK is less common than PGE, disease onset can be sudden and severe.
Figure 3: Pale mucous membranes of the eyes are an indication of severe anaemia.
Given the presenting signs described above, Haemonchosis can appear similar to Fasciolosis. Diagnosis to further distinguish can be achieved through:
Haemonchosis can be treated with most anthelmintic products, although some evidence of resistance to white drenches (1-BZ) has been reported previously in the UK. Some flukicidal products, such as nitroxynil and closantel are also effective against Haemonchus contortus and should be considered in certain cases.
Adult tapeworm segments may be seen in the faeces of lambs during summer months (Figure 4). These are acquired through consumption of infected intermediate hosts (orbatid mites) living on the pasture.
Monezia species tape worms are generally not considered as a cause of disease in livestock. Roundworm treatment with a white drench (1-BZ) is generally effective against these tapeworms.
Figure 4: Tapeworm segments (Moniezia) are commonly seen in faeces passed by lambs during the summer months. These are generally considered non-pathogenic.
Failure to treat fly strike promptly is a welfare issue and can lead to disrupted grazing, loss of condition, secondary infections and death (Figure 5).
Disease severity depends upon a variety of factors including weather, with warmer, humid conditions favourable. The NADIS blowfly alert is based on daily temperature and rainfall data and is updated every 2 weeks over the course of the grazing season. This was predicting moderate risk for most of England, Wales and Northern Ireland by the end of May.
Figure 5: Blowfly strike is a major welfare concern, often resulting in death if left untreated.
Advised actions include:
The situation with PGE in cattle is similar to that described for sheep, although the worms which cause disease are different. Of these, the brown stomach worm (Ostertagia ostertagi) is the most important, although co-infection with other roundworms such as Cooperia can contribute to and further exacerbate disease, characterised by a loss of appetite, weight and body condition accompanied by profuse diarrhoea (Figure 6).
Calves and young stock are most at risk, particularly autumn and winter-born weaned calves entering their first grazing season and spring-born beef suckler calves entering their second grazing season, with PGE reducing growth rates by up to 30%. Additionally, adult cattle may also experience performance limiting disease if grazing heavily contaminated pastures; PGE may reduce a lactating dairy cow’s daily milk yield by up to 1 kg per day.
Temperature plays an important role in development and survival of eggs and larvae at pasture, with faster rates of development at higher temperatures. The above average temperatures observed over the preceding 3 months (March – May) could therefore increase the level of pasture expected at this time of year.
Figure 6: Clinical cases of PGE are typically characterised by loss of appetite accompanied by a profuse, green diarrhoea affecting large numbers of animals.
To control PGE in cattle:
Advised actions include:
Lungworm infection (or “husk”) can occur from June onwards. Outbreaks are difficult to predict, but may be associated with wetter summers and following periods of wet weather. In areas where lungworm is known to be present, it is recommended first season calves are vaccinated prior to turn-out.
Unvaccinated calves and those not part of strategic dosing programmes should be considered at risk. Older cattle may also be at risk if they have not developed an effective immune response previously. This can be due to a lack of previous exposure, notably bought-in cattle on farms with a known history of lungworm. Effective worm control in previous seasons not allowing immunity to develop - vaccinated animals require subsequent natural exposure to lungworm to develop full immunity.
Advised actions include:
Figure 7: Lungworm larvae passed in the faeces of infected animals can be used to diagnose infection
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