Liver fluke - "What is it costing you?"

Live weight gain can be reduced by over 10% in ewes and up to 30% in lambs, which in a flock of 500 ewes could cost as much as £26,000 per year as a result of the direct costs of treatment, mortality and production losses.

That was the message at a meeting on liver fluke in sheep and cattle held by Myerscough Vets in assocaition with Myerscough College under the RDPE Northwest Livestock Programme.

The speakers for the evening were independent vet Debby Brown and Nick Davies, agricultural group manager for Dunbia.

Fluke life cycle

Debby kicked off with a look at the pathology of the disease and how it is spread.

Liver fluke is caused by a parasite (Fasciola hepatica) which resides in the bile duct and liver of sheep and cattle. However the parasite is not host specific and it also requires a mud snail to act as a host in order for it to complete its full life cycle.

• Adult fluke produces eggs which are passed out onto the pasture in the faeces of infected cattle/sheep.
• The eggs hatch in warm, wet conditions to produce larvae which then infect the mud snail.
• The larvae develop in the snail host and then the immature fluke pass out in cyst form onto the grass.
• These larval cysts are ingested by grazing cattle and sheep, and once in this host the pH of the rumen breaks down the cyst to release the fluke.
• The immature fluke migrate to the liver to feed, causing considerable damage.
• The fluke then move to the bile duct where they mature and produce eggs – and the cycle starts again.

One adult fluke is capable of producing 25,000 eggs per day, hence the very rapid spread of infection.

Risk factors

Survival of the snail host (and hence the fluke parasite) is favoured by warm, wet conditions and so the incidence of liver fluke is affected by weather conditions, both in the autumn of the previous year and the summer of the same year. However it must be remembered that even in drought conditions the parasite can effectively hibernate in a wet patch in the field and then begin to multiply once the weather becomes more favourable for them.

The main ‘risk times’ for infection are:

April-June – the larvae which have over-wintered in the snail host cause infections in late summer/early autumn

Aug-Nov – fluke eggs which have over-wintered on pasture or new fluke eggs shed in spring which are then picked up by the snail in spring. The cysts cause winter infection in stock.

The disease

There are three forms that the disease can take in livestock:

• Acute fluke – large numbers of immature fluke migrate to and burrow through the liver causing widespread damage and resulting in rapid loss of condition and sudden death. More likely to affect sheep than cattle as cattle tend to have greater resistance and also have larger livers which can tolerate higher levels of damage than small sheep livers. Occurs very quickly after infection (1-3 weeks in sheep, 1-5 weeks in cattle)
• Subacute fluke – smaller numbers of fluke burrowing through the liver and occurs less rapidly after infection than in acute cases. Relatively less damage to the liver resulting in a steady loss of condition in infected stock.
• Chronic fluke – this is the most common form of the disease with symptoms including anaemia, loss of body condition, accumulation of fluid under the jaw (bottle jaw). Can predispose the infected animal to other diseases (such as clostridial diease, metabolic disease and parasitic gastroenteritis) due to impaired liver function. Caused by the adult fluke feeding in the bile ducts, where they can consume up to 0.5ml of blood/fluke/day!

Financial impact

In terms of the costs incurred as a result of liver fluke infection, these are determined by the loss of production and also the cost of treatment. Animals affected by fluke will have poor growth rates and overall performance due to the parasitic burden and also the impaired liver function.

In ewes live weight gain can be reduced by over 10% and in lambs this can increase to 30%. Debby calculated that in a flock of 500 ewes with 15% of the land undrained (providing the ideal habitat for snail survival) the cost of fluke can be over £26,000 per year as a result of the direct costs of treatment, mortality and production losses.

Are your stock infected?

The symptoms seen in stock affected by fluke are not specific only to this disease so testing is necessary to determine whether or not your stock are infected. The best method will depend on the species.

Faecal egg counting (FEC) is the best method for sheep as this will give an idea of the number of eggs being shed in the faeces and hence the severity of chronic infection. January is the best time for FEC as the flukes are most likely to be mature and producing eggs at this time.

Blood sampling is used more often in cattle, although it tends to be less specific than FEC as the accuracy depends on the test and timing. In dairy cattle bulk milk testing is often used to detect fluke.

Post mortem liver samples taken in the abattoir will give very accurate feedback as to whether fluke is a problem in the liver – however by this point it is too late to do anything for that particular animal. This information can be used in the future to work out the probability of other stock on the farm being similarly affected.

Treatment

Treatment for liver fluke infection is again dependent on species and also the level of risk on that particular farm.

Sheep

High risk areas: dose in September with a flukicide that is effective against all stages of fluke (mature & immature). If stock are badly affected then treat again after 6 weeks (or at two weeks post-housing if housed). Treat in the spring with a product effective against adult fluke.

Lower risk areas: use FEC or post-mortem to determine first whether there is an issue with liver fluke. If so then dose against all stages in either October, pre-tupping or 2 weeks post-housing. Dose again in spring using a product for adult fluke.

Cattle

Dose at housing against all stages. If stock are wintered outside, particularly in wet areas, they may require more dosing – in October against all stages, in January against immature fluke and in spring against adults.

Control

As with any disease, prevention is better than cure and liver fluke is no exception.

• Prevent stock entering typical snail-friendly habitats such as wet areas (ponds, river banks etc.) Alternatively by draining the land wet areas may be prevented. However Debby did appreciate that this approach is not always possible, particularly on farms with a lot of heavy wet land.
• In years of drought take care to ensure that livestock can’t get to wet holes eg. tyre ruts where water will collect, as these are the areas that stock are most likely to choose to drink from.
• Use the NADIS fluke forecasts to monitor the level of risk and manage your land/grazing accordingly.
• Work closely with your vet if liver fluke is diagnosed as they will help you to develop a control strategy specific to your farm to give maximum benefit without risking resistance building up to the products available.

Resistance

The build up of resistance to products used for worming is well documented and it is no different for the products used to kill liver fluke. The more these products are used, particularly if they are used routinely when there is no real need for them, the greater the risk of resistance developing with the very real danger that we may end up in the future with no effective treatments for fluke.

In order to slow-down the development of resistance the SCOPS recommendations must be adhered to:

• Test for resistance on your farm – carry out a FEC prior to dosing then another one after dosing. If the flukicide is working effectively the egg count will be reduced by at least 95%.
• Dose only when necessary – use forecasts and historical data from your own farm to determine the times of highest risk.
• Dose stock correctly – always dose to the heaviest in the group and calibrate the dosing gun to ensure it is administering the correct amount.
• Treat sheep in quarantine – any bought-in stock should be treated whilst in quarantine, particularly if coming from a high risk area, then turned out onto a dirty pasture.
• Preserve a susceptible worm population – much easier with worms than liver fluke.
• Reduce dependence on anthelmintics – manage grazing to help reduce the burden/risk and perhaps investigate using sires which have been bred for resistance.

The effect on the industry

Nick Davies from Dunbia then spoke about the financial implications of liver fluke from the point of view of a processor.

He started with a quick overview of Dunbia and the global market that they supply just to put into perspective the impact that the world market and economy has on the UK meat market and prices. In general the higher value meat products such as joints and steaks are sold into the European market, whereas less wealthy continents such as Africa and Asia have high demand for animal products from what is deemed as the fifth quarter. Products such as offal, tendons, testicles and even knee caps, are considered in other parts of the world as delicacies and we need to ensure that this important market is not ignored.

Liver adds value overall to the carcass and hence it is in the interest of the industry as a whole that the liver is of the best possible quality. Obviously the damage caused by liver fluke deems the entire liver unfit for human consumption and thus vastly reduces its value, which then devalues the whole carcass.

How can you be sure that your stock are not infected with liver fluke?

Nick posed this question to the group and very few farmers could say for definite that they were sure that liver fluke was not an issue on their farm. As Debby mentioned earlier the symptoms seen in animals suffering from liver fluke are not specific and testing is necessary to provide a definite diagnosis.

Liver inspection

All of the stock slaughtered at the abattoir are post-mortem inspected by the Meat Hygiene Service and part of this inspection involves looking at the liver to determine whether or not it is fit for human consumption. For those farmers that sell direct to the abattoir this information is readily available and will provide invaluable information about the health of your stock – all you need to do is ask.

Nick then showed the group some pictures of livers infected with liver fluke – not pleasant viewing but it certainly gave an appreciation of why animals infected do not perform at the optimum level due to the damage in the liver!

The cost

Nick shared with the groups some findings from studies carried out by Dunbia into the proportion of livers condemned due to fluke. 34% of sheep livers are rejected on a daily basis. This can be multiplied up by the number of sheep slaughtered annually equating to 1.9 million livers rejected per year. These livers would be worth over £800,000 if sold for human consumption, but only £170,000 when sold for dog food, hence a loss of well over £600,000 annually.

The figure is much greater in cattle due to the fact that cattle livers are bigger and so more valuable, but also due to the fact that 50% of cattle livers are rejected daily due to fluke damage. On the 475,000 cattle slaughtered annually this adds up to losses in the region of £1.28 million.

In addition to this loss being a huge problem for the abattoir it is a problem for the industry as a whole as it affects the price which is paid for carcasses. The potential to add value to the carcass and also to ensure increased production from the livestock just by better control of liver fluke in the UK is enormous.

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