Parasites pose threat to winter stock

The threat to productivity from parasites in sheep and cattle should not be ignored over the winter period, warns Merial Animal Health, as the NADIS Parasite Forecast for December highlights specific areas of concern.

In sheep, the predominantly dry weather during autumn may have prevented worm larvae from leaving dung and migrating to the pasture, but the more recent wet weather means that the risk of infection is likely to increase, particularly from trichostrongylosis.

Sioned Timothy, Veterinary Adviser at Merial Animal Health, says: “In many cases, farmers won’t be accustomed to drenching sheep so late in the year, but heavy infestations of trichostrongylosis can cause black foetid diarrhoea and associated weight loss. Monitor at-risk animals, including gimmers and store lambs, with pooled faecal samples and treat accordingly.”

Haemonchus larvae that have been acquired from pasture will arrest their development in the stomach wall as the temperature drops. Faecal egg counts will not identify the encysted stage of the larvae, so where haemonchus is a known problem in flocks, treatment may be warranted to prevent the encysted larvae emerging on-mass in the spring, causing severe production losses.

Rams which have lost weight after tupping may be at increased risk of parasitic disease. Faecal egg counts will identify those individuals which would benefit from a worm control treatment before spring. Supplementary feeding may also be required, as improved nutritional status will increase resilience to larval challenge.

External parasites will often cause problems in flocks at this time of year, resulting in weight loss from disrupted feeding patterns, damage to fleece and trauma from scratching. Populations of lice reach their peak over winter, spread by direct contact between animals, and burdens are often most severe in ewes in poor condition.

“The symptoms of a louse infestation can easily be confused with sheep scab, so it’s vital that farmers ask their vet for a diagnosis before attempting treatment. Particular care should be taken to follow the data sheet guidance on application techniques when using topical products on sheep in full fleece or their efficacy may be compromised,” advises Ms Timothy

Keeping on top of fluke control should be a priority for sheep farmers over the winter period. Targeted treatments will reduce egg output onto the pasture, lessening the risk of disease in 2016.

“Sheep in the high fluke risk areas (western Scotland and north west England) that received up to two treatments of triclabendazole during the late summer and early autumn should now be able to delay further treatments until the New Year,” says Ms Timothy. “In January, an alternative product containing either nitroxynil (Trodax®) or closantel which is effective against late immature and adult fluke should be used.”

In other parts of the UK, it is likely that a second treatment with triclabendazole will not have been required. Farmers in the south west of England, Wales and eastern Scotland should also consider the use of either nitroxynil (Trodax®) or closantel in late December or January. Using a product other than triclabendazole at times of the year when acute fluke is not a risk will reduce the selection pressure for resistance, whilst still effectively controlling the later stages of fluke which pose a risk to livestock at this time of the year.

Housed cattle should receive targeted fluke treatments to ensure that their growth and productivity is optimised over the housing period and that they are fluke-free at turnout. The choice of product and timing of treatment will be dictated by the treatment protocol at housing. Similarly, outwintered cattle which may have been exposed to a parasite challenge later in the season should be treated to ensure they do not carry fluke burdens into spring.

In the majority of cases, triclabendazole treatment is unnecessary over winter. Choosing an alternative product when their use is appropriate, such as one containing nitroxynil (Trodax®), closantel or albendazole, will reduce the selection for triclabendazole resistant fluke.

“If farmers are unsure of the fluke status of their herd, the quickest and cheapest way to identify a fluke infection is to request abattoir feedback on any liver condemnations,” says Ms Timothy. “The report can be used to guide an appropriate treatment plan in conjunction with their vet or SQP (Suitably Qualified Person).”

The main worm threat facing growing cattle (beef and dairy) over winter comes from gutworm (Ostertagia ostertagi) larvae which encyst in the stomach wall over winter. Yearling cattle are most at risk, particularly those that have been exposed to heavy challenge at grass over the summer of 2015.

If left untreated, the sudden resumption of the larvae’s development in late winter and early spring will cause acute scour from type 2 ostertagiosis with the risk of fatalities in severe cases.

It’s important that the wormer chosen will effectively treat the encysted stage of the larvae. A SQP or vet will be able to advise on the most appropriate product.

Lungworm outbreaks are less likely as winter progresses. However, any coughing in un-wormed stock during housing should be investigated, as lungworm infections acquired late in the grazing period mean disease is still possible.