This condition is caused by the spores of the fungus Pithomyces chartarum. The fungus grows on pasture in areas with high temperatures and high humidity (typically warmer North Island districts). Ingestion of fungal spores can cause acute damage to and blockage of the bile ducts. This results in liver damage, jaundice and photosensitive dermatitis.
How does the problem spread?
The fungus produces spores which contain a toxin known as sporidesmin. When spore levels get over around 40,000 spores per gram of pasture then deer are considered to be at risk from eating the pasture, especially if spore counts stay high for several weeks.
What are the symptoms?
Clinical symptoms include a much larger range than seen in sheep or cattle. In deer they can include poor growth or weight loss (especially in weaners), swelling inside the nose (caused by photosensitivity), skin ulceration of the muzzle and tongue, and lameness. Deer will rub areas irritated by photo sensitisation, particularly the muzzle, eyelids and ears. Occasionally deer can become blind but this indicates severe liver damage. Chronic scouring, blood in the urine and problems with urinating (arched back) has been observed in affected deer, suggesting that the toxin can also affect the intestine and urinary systems. Affected deer may seek shade but photosensitivity is not seen in all cases.
Membranes around the eye may appear yellow, as a result of jaundice. Respiration may be elevated (panting). Acute laminitis was observed in 2% of weaner deer in a mob during a high-toxicity period. The front feet became malformed. Autopsies of affected deer have shown varying levels of liver damage (from minor to major). Repeated or severe chronic damage can cause permanent liver damage (swollen if acute, shrunken if chronic).
Effect on deer production
Facial eczema is the biggest animal health problem for North Island deer. Production effects are very significant. The Northern Region Deer Industry Focus Farmers found that in years with high facial eczema levels, hind conception rates were lower.
Fallow and Elk seem to be more susceptible than Wapiti and Red deer. Mature stags prior to the rut are at greater risk as they are rapidly increasing pasture consumption. Dry hinds are moderately resistant but sporidesmin effects are cumulative so some hinds may end up with damaged liver function, making them unable to gain weight over winter or lactate effectively in future seasons.
This is done by observing for clinical signs and/or elevation of the enzyme gamma glutamyltrasferase (GGT) in the blood. In one set of observations GTT levels were not high in deer showing clinical signs of facial eczema.
Control and treatment
The first step to controlling the problem is to know the spore levels over the high risk period (summer/autumn). District spore counts are available weekly at http://www.asurequality.com/facial-eczema-reports.cfm . These indicate what is happening across a district but individual paddocks on a farm may already be high.
- Starting paddock spore number monitoring prior to the high risk period and taking action early is the best option. It allows time to plan a suitable grazing rotation and spray plan. Veterinarians offer spore counting services.
- Find out the age of the spores. Older spores are less toxic than younger. North facing areas tend to have higher spore counts than south facing.
- Monitor weather conditons as several warm nights in a row can greatly lift spore numbers. Metservice has a risk warning service http://rd1.com/weather/facial-eczema
Spore levels above 40,000 is considered to be a risk. During 1999 spore counts in the Waikato over 400,000 (i.e. ten times this) were common.
Once a risk is established, minimising toxin ingestion and effects can be done several ways.
- Swap pasture in the diet with summer turnips, maize silage, chicory, plantain, short-term ryegrass or clover.
- Minimise dead litter in pastures and adjust grazing so deer are not forced to graze pastures too low.
- At critical times spray the farm with carbendazin fungicide at 150 grams/ha. Typically this might be twice during the season.
- Delay weaning until spore counts drop to safer levels (i.e. under 50,000)
- Administer a zinc bolus (traditionally given to sheep). However they have varying degrees of effectiveness and can be difficult to administer. In one case up to 8% were regurgitated.
- Add zinc monohydrate to farm water supply.
- Keep pasture quality high as spores prefer to grow on aged/dead material.
- Select for deer resistant to facial eczema.
Prior exposure of deer to toic spores makes them more susceptible so try and keep them protected at all times.
Treatment should include keeping deer in a dark shed or provide shade for four to six week. Provide fluid and vitamins to aid recovery.
Click here to see a factsheet on facial eczema prepared for deer farmers.
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