Facial eczema (FE) is a disease of ruminants which causes liver damage. This can lead to lowered production or even death. The disease is caused by a fungus – Pithomyces chartarum – which under the right environmental conditions produces spores containing the toxin sporidesmin. Sporidesmin causes direct injury to the liver, the bile ducts become thickened and may become completely blocked. The skin damage seen is secondary to the liver damage. One of the livers functions is to break down waste products. When damaged it cannot do this properly and these waste products build up. One of these is a product of chlorophyll (which comes from the grass). This product accumulates in the tissues and causes sensitivity to sunlight. The appearance of skin damage results from spores consumed 1 – 2 weeks ago. Even if the liver damage is insufficient to cause photosensitization there may still be ‘sub-clinical’ effects on the production of milk, meat and wool. If you have a few animals showing clinical signs of toxicity it is likely that the rest of the herd/flock will be affected to some degree.
The risk time for FE is typically during the late summer and autumn. For rapid growth and spore formation the fungus needs warm, moist conditions. Soil temperatures typically need to stay above 10°C for rapid increase in spores. Heavy dews can contain enough moisture to encourage spore formation.
The toxicity of a pasture to your stock depends on more than just the spore count. Other factors to consider include the grazing intensity of the stock (animals grazing down low will consume more spores), the age of the spores (older spores are less toxic). There is wide variation in the susceptibility of animals within and between breeds and species. Prior exposure to spores also makes animals more susceptible.
Generally however, spore counts over 30 000 spores/gram of grass are mildly toxic. Counts of 50 – 80 000 are moderately to highly toxic. Spore counts above 100 000 can’t be fully protected against by zinc.
Species vary in their susceptibility to FE. Fallow deer and sheep are most susceptible, followed by cattle and red deer. Goats are more resistant. Breeds vary within species, and do flocks/herds within breeds and individuals do within flocks/herds.
Sheep – clinical signs include increased restlessness, head shaking, scratching, rubbing and shade seeking. The exposed areas of the skin around the face and ears become swollen and thickened. The ears may droop. There may be serum oozing from the skin which will form scabs.
Cattle – in dairy cattle you will see a marked drop in milk production. This may occur some time before skin lesions are observed. The animal will be restless at milking and seek shade. There may be thickening and peeling of exposed or thin skin. White areas, the udder and teats, the muzzle and the coronets are usually the most affected.
Deer – the lips and muzzle and areas around the eyes are most affected. They will be restless and irritable and actively seek shade. They frequently lick their muzzles and lips.
Goats – will seek shade. They may develop crusty lesions about their eyes and lips and the ears may become thickened.
Facial eczema is a 'tip of the iceberg' disease meaning that only the worst cases ever show the external symptoms and most only have the underlying (sub-clinical) liver damage. If you are seeing clinical cases in some of the herd/flock it is likely that there will be many more affected. Liver damage will result in production losses (milk, wool, live weight gain), reproductive losses and secondary diseases e.g. an increase in metabolic diseases. If you think your herd is suffering from sub-clinical disease we can take blood samples to confirm if this is the case.
Supplementation with zinc needs to start at least 10 days prior to spore counts going up. Zinc doses can be increased (by 50%) for short periods of time (10 – 14 days) if spore counts get very high (over 100 000). Stock should not be exposed to zinc unnecessarily and excessively prolonged zinc dosing lowers the safety margin.
Daily zinc oxide drenching is best for dairy cows.
Aim to give 2.6 gm ZnO/100 kg.
Mix 1 kg ZnO with 1 litre of water slowly and stir.
200 ml of a stabiliser (eg – liquid seaweed fertilizer) can also be added to make mixing easier.
Long term dosing – 3 ml/100 kg/day. Give 3.6 ml/100 kg/day if a stabiliser is used.
3 day dosing can be used. Give 15 ml/100 kg. Do not drench milking animals less frequently than every 3rd day as the amount of zinc given can induce milk fever.
Dry stock can be drenched weekly, but it is at a higher rate. Use 9 times the daily dose.
Trough treatment is only reliable in dairy cows which have to drink water. Trough treatment in dry stock can be hit and miss because they can choose not to drink water to some extent. Zinc tastes bad and stock need to get used to the taste. If there are other sources of water around they will drink this instead. It is a good idea to start at ½ dose rates about January and increase to full dose rate when spore counts start to climb. Flavouring can be used to disguise the taste.
Monozinc – 5.5 g/100 kg/day.
Heptahydrate – 8 g/100 kg/da.y
Inline dispensers are best as all animals drink the same concentration. Direct treatment of trough or in trough dispensers may only treat a small proportion of the herd.
Zinc bullets are an excellent way of preventing eczema in dry stock. Protection lasts for 5 – 6 weeks. Toxicity can occur if more than 3 administrations are given so it is best to watch spore counts and avoid putting them in too early. Use the right weight range bullet for adequate protection. They come for all sizes from lambs to cattle up to 400 kg.
Fungicide sprays are only useful before the spore counts go up. Fungicides to not kill spores that are already present. Properly treated pastures should remain safe for 4 -6 weeks.
The fungus responsible for FE lives on dead matter and the spores are generally found at the base of the pasture. To help reduce the number of spores ingested you can (if possible):
Minimise the build up of dead litter matter - keep pasture quality high.
Identify and avoid grazing paddocks that are known to have high spore counts.
Keep the grazing pressure to a minimum
Feed supplements instead of toxic pasture.
Make sure affected animals have access to shade.
Skin lesions can be treated with filta bac or similar cream .
Severely affected dairy cows should be dried off.
Supplementing stock with safe feeds will prevent further damage.
Some dietary supplements (e.g. sea weed extract or LiverX) are reported to help restore liver damage in recovering cases. Monthly B12 injections help stimulate appetite.
Skin damage in some of the herd/flock indicates that there is liver damage in the whole mob. However there is not a good correlation between skin damage and liver damage. Liver damage can be assessed by blood tests.
The most useful indication that a clinical case will recover is that it returns to some sort of productive state, e.g. milk production or weight gain in < 1 month from first clinical sings. If still struggling after 2 months culling may be the best option.
Preferential treatment should be given to eczema affected stock. The following spring will be a very stressful time for these animals. Ad lib feeding and time is the main pre-requisate for recovery. Special attention to transition management will reduce the risk of metabolic disease in these highly vulnerable cows.
Zinc toxicity – Overdosing with zinc can be toxic. Calculate, measure and administer zinc carefully.
Zinc accumulates in the liver and kidney and therefore animals should not be treated with zinc for 7 days before going to slaughter.
Long term zinc dosing may interfere with copper uptake and vice versa.
When spore counts in your area get high, it is a good idea to take samples from all over your farm to determine which paddocks are your worst paddocks. This will allow you to adjust your grazing management and prevention strategy when dealing with hot paddocks.
Resistance to facial eczema is known to be hereditary in sheep and this is thought to be the case in cattle. There are ram breeders that select for FE resistance.
Take care if supplementing stock with injectable copper during the autumn. Liver damage can remain long after clinical signs have dissapeared. If unsure, get a small portion of the herd blood tested to see if liver damage could cause copper toxicity, or use another form of copper supplementation.