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Wednesday, 29 October 2008 16:56

Facial eczema (FE)

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facial eczemaWHAT IS IT?
  • FE is a disease of sheep, cattle, goats, and deer. It also affects alpacas but not horses
  • Affected stock show photosensitisation or sunburn which can be severe, and animals are very uncomfortable, irritable from the itch and obviously in discomfort or even pain.
  • The skin damage is secondary to liver damage, and both together can result in ill-thrift, lowered milk production, low fertility, metabolic diseases and death.
  • Severe cases can be so bad that the animals should be euthanased.
  • Affected stock sent to the works may be condemned.
  • They should not be kept for home kill for human consumption.
WHERE AND WHEN DOES IT OCCUR?
  • It’s mainly a disease of the North Island but it can also occur on the west coast of the South Island, the Nelson area and in Canterbury on irrigated dairy pastures.
  • The warm, moist summer and autumn conditions on dry pastures after rain or heavy dews bring it on. It can start in January and can carry on till late May, as long as soils are warm.
SIGNS
Sheep
  • The first signs in sheep are drooping ears and swollen eyes, so the sheep may be effectively blind.
  • Affected sheep shake their heads and rub their eyes on fence posts and gates, which causes sores and bleeding.
  • Sheep are desperate to find shade and are loathe to come out to eat or drink.
  • Their lesions are often attacked by blowflies.
  • Badly affected sheep stop eating and often die very quickly.
  • On post-mortem they have abnormal hard misshapen livers and jaundiced fat.
Cattle
  • The first signs are reddening and flaking skin on hairless skin and white skin areas exposed to the sun, i.e. the skin along the back, under the front legs, the udder and teats and around the eyes, ears, and nose.
  • Animals are restless and are desperate to find some shade.
  • They try to nibble the affected areas, which are itchy particularly when wet from rain.
  • The flaking skin sloughs off (often in great lumps) and the raw flesh left beneath can become infected and very sore.
  • The bare skin of the udder and around the vulva can be affected. The teats can be severely affected, and become raw so cows cannot be milked.
CAUSE
  • Facial eczema is caused by a toxin (sporidesmin) produced by the spores of the fungus (Pithomyces chartarum) in pasture. Under the microscope, the spores are a very characteristic hand-grenade shape.
  • The fungus grows in the dead litter at the base of the pasture in warm moist conditions and can also grow on the base of green plants.
  • There is great variation in spore counts between paddocks and within the same paddock on the farm. For example, there can be high spore counts in the shaded lower sheltered areas, and no spores on open faces and high slopes.
  • The young rapidly growing spores are most toxic. Old spores are not such a problem.
  • The toxins from ingested spores are eaten and damage the liver which cannot get rid of phylloerythrin, a chlorophyll breakdown product, and this circulates in the blood.
  • Phylloerythrin releases energy and when exposed to sunlight causes skin damage identical to severe sunburn.
PREVENTION
  • Currently, there is no cure for FE so prevention is the best option.
  • Don’t wait until you or neighbours see the first clinical cases before acting. By the time 5% of a flock or herd show obvious clinical signs, up to 70% of them will have liver damage.
  • Prevention is based on knowing when spores are multiplying and “spore counts” are high, and hence when pastures are “hot”. This is done by spore monitoring (see below).
  • The basis of all prevention is treatment with zinc salts. Zinc oxide is used as a drench, and zinc sulphate is put in water supplies.  Make sure you get this right, as zinc sulphate is very toxic if drenched.
  • It takes at least 3 weeks after the start of zinc treatment before enough reserves are built up in the liver to be effective. This is the major reason for failures as some people expect instant results after they see clinical cases.
  • Zinc treatment can never be 100% effective, so in severe outbreaks expect problems. When pastures are really hot with high spore counts, then increase zinc dose rates. Consult your veterinarian about this.
  • Remember to order your zinc early as stocks often run out in severe seasons.
  • It’s very important that only licensed animal remedies or approved medicines are used for FE prevention.
  • Spraying pastures to kill fungi was one of the earliest ways to prevent outbreaks of FE, and it’s still an effective option for small areas to make them safe.
  • New products are always coming on the market so check with manufacturers about use and how long products last, as this will depend greatly on weather conditions. Keep checking spore counts on these sprayed pastures to make sure the product is still effective.
  • Supplements e.g. Hay or silage can be fed on these safe areas..
  • Growing a crop to feed out during the most dangerous FE period has been a recommended practice in the past. Costs need to carefully worked out as there are risks in knowing how much crop to grow, how much it will yield (it’s very rain dependent), and hence how long it will last. You will also have to factor in how long the paddock will be out of grass and the costs of reseeding.
  • It took 30 years of dedicated research at Ruakura Research Centre in Hamilton to work all this out, but prevention methods have been known now for 40 years.
Sheep
  • It's not practical to drench sheep at regular intervals with zinc oxide, so a slow-release bolus is available to be put down the animal’s throat into the rumen. It lasts for 42 days.
  • It’s very important to follow the manufacturer’s instructions about administration to avoid injuring the animal‘s gullet.
  • The interval before re-dosing is also critical. Six-week intervals will ensure all the old bolus is fully used up before a new one is given. More than one bolus in the rumen at the same time can cause zinc toxicity.
  • After three boluses over a long FE season, animals often start to show the effects of too much zinc. They may need copper supplementation, as excess zinc strips copper from the liver. Consult your veterinarian about this.
  • When pasture spore counts are high, sheep can be confined to bare areas or yards and fed hay, silage or nuts. Some sheep will not eat hay or nuts if they haven’t encountered them before but they may take to silage more readily.
  • When introduced to crops, it may take a few days before sheep start to feed. Sheep on a crop need a good water supply.
  • Water trough treatment with zinc is not effective for sheep because they don’t drink as regularly as cattle.
Cattle
  • The usual and most effective prevention for FE in cattle is to drench with zinc oxide.
  • With milking cows this is easy to do at each milking, until the cows are dry. If FE is still a risk when they are dry, they are drenched weekly.
  • To avoid this extra work, most dairy farms now have an in-line zinc supplementing system which delivers zinc to each trough.
  • It’s important to check the mixing recipe and the actual amount of zinc each beast should get. It needs to be increased when spore counts rise rapidly.
  • It takes time for cattle to accept the taste of medicated water and it helps to add a sweetener.
  • Regular drenching of beef cattle is not practical so water trough treatment with zinc sulphate is possible, provided cattle are not drinking from dams or creeks.
  • The zinc bolus is probably the best alternative before pastures become ‘hot’, accepting the challenge of dosing large cattle. A headbail is essential, again being very careful to have the head in the correct position to avoid damage to the gullet.
  • Hill country beef farmers often just put their cattle on their highest country where spores are less likely to be found.
  • Zinc supplements should be started in January and it is important not to risk overdosing by doubling up on methods.
  • Cattle have no problem taking to hay, silage or a crop when fed on a bare area while spore counts are high.
  • Spraying can be effective to produce protected areas either for grazing over the danger period, or to feed out supplements during hot spore periods. Follow the manufacturer’s instructions carefully, and monitor spore counts to check if the spray has worked and if it’s still effective.
  • There are risks when stock are concentrated on bare land or short pasture for too long as  stress can predispose them to diseases such as salmonellosis.
  • As there is lasting liver damage, consider culling milking cows rather than keeping them for another lactation. If you do keep them, be prepared for metabolic diseases, especially milk fever at calving.
  • When buying cows after a bad FE year, it would pay to request blood tests for GGT to test liver function before purchase.
LONG TERM SOLUTIONS
  • Replacing affected pastures with improved ryegrass cultivars or other species that won’t support the fungus is a good long-term prevention strategy. Check with your seed merchant for the latest information.
  • FE resistance in sheep is strongly inherited so buying rams from breeders who are selecting for resistance will bring about improvement in your flock.
  • Check with the breeder about the level of sporidesmin used in their tests and the length of time they’ve been testing.
  • Consult your veterinarian on the merits of GGT testing to select replacement ewe hoggets. It may be cost-effective on some farms.
  • Gene markers for FE resistance have been found and are being actively researched in both cattle and sheep.
  • FE resistance is known to be inherited in dairy cattle and research is ongoing.
  • Work on deer and camelids is yet to be done.
  • Other solutions such as altering the infective fungus are still being researched.
TREATMENT OF AFFECTED ANIMALS
Sheep
  • Sheep with clinical FE must be treated under the law so seek veterinary help. Severe cases will have to be euthanased.
  • At the first signs of FE, provide shade and drench with zinc oxide. Shade is critical. It may be too late for the zinc oxide to do much good.
  • Opaque protective cream can be applied to damaged skin, to hasten healing and to screen the skin from sunlight.
  • Put badly affected sheep with swollen eyelids and poor vision in a safe paddock and avoid the stress of handling.
  • For small flocks, put them in a shed out of the sun during the day and let them out to graze at night,
  • Affected sheep need good feeding to help recover, but feed them some high energy concentrates rather than high protein lush green grass which their livers cannot handle.
Cattle
  • At the first signs of FE, affected animals should be given shade and drenched with oxide. Shade is critical. It may be too late for the zinc oxide to do much good.
  • Take them off the ‘hot’ pasture either to a bare area to feed supplements or to some other safe part of the farm.
  • Opaque protective cream can be applied to damaged skin, to hasten healing and to screen the skin from sunlight.
  • Your veterinarian can give antibiotic injections to treat skin infections that occur if animals are severely affected and vitamin B12 injections can help to boost appetite.
  • Severely affected dairy cows with areas of sloughed skin should be fitted with a cover provided it does not chafe and add to their suffering. Dry off dairy cows with severe signs, especially those with udder and teat damage. Flies can be serious irritants.
MONITORING
  • Spore numbers are measured by collecting a sample of pasture and shaking it up in a jar of water. A sample of the liquid is inspected in a special slide under a microscope to count the spores. Check with your veterinarian for details.
  • Kits are available to do this at home, or veterinary clinics provide a service.
  • The best idea is to sample specific “monitoring” paddocks e.g. shaded sheltered areas where spores are likely to grow. This is better than just random sampling paddocks on the farm.
  • You can find out about current spore levels at veterinary clinics, in local newspapers.  Beware of local rumours.  They may not be relevant to your farm, especially when they say the danger is low!
Dr Clive Dalton

Clive did a Ph.D. in sheep breeding at the University of North Wales at Bangor. After lecturing at Leeds University, he came to New Zealand to do research with MAF. Because of his communication skills, he moved to the Ruakura Agricultural Research Centre to be fully involved in interpreting science for practical application by farmers.

After 14 years he moved to teach at the Waikato Polytechnic where he taught young future farmers. He won the 1993 Landcorp Communicator of the Year award and the 1999 Sir Arthur Ward award for agricultural communication.