Facial Eczema
Pithomyces chartarum: A summary of information
Article by Janie Hicks of Coolaroo.
Introduction
Pithomyces chartarum is a common fungus that grows on dead vegetable matter in pastures. P. chartarum contains a toxin called sporidesmin and grazing of pastures with high spore counts can cause significant disease in sheep, cattle and goats but some species of deer and alpaca appear to be at higher risk.
The disease caused by the ingestion of sporidesmin is called facial eczema (FE). This disease is not really an eczema, it is a condition associated with liver damage (Hungerford, 1975). A secondary effect of liver damage is photosensitization where non-pigmented skin reacts to light hence the name “eczema” (Hungerford, 1975).
The fungus is widely distributed and has been the cause of serious disease in sheep and cattle in New Zealand for over 100 years, but outbreaks have also occurred in Victoria (Hore 1960), New South Wales (Dent and Rofe 1967; Greenwood and Williamson 1985) and Western Australia (Gardiner and Nairn 1962; Edwards et al. 1983).
The Disease
Facial Eczema (FE) is a disease of sheep, cattle, goats, deer and alpaca which causes lowered production, suffering and death from liver injury. The pathology and pathogenesis of the disease has been described and reviewed by Mortimer (Mortimer 1963; Mortimer et al. 1978).
The earliest clinical signs of the disease are increased restlessness, head shaking, scratching, rubbing of the head and shade seeking behaviour. Unthriftiness and poor appetite may be evident. These symptoms will generally occur from ten days to several weeks after exposure to the toxic pasture.
Sporidesmin causes the bile ducts to become thickened and may be completely blocked. The damaged liver cannot rid the body of wastes and a breakdown product of chlorophyll accumulates in the tissues and causes sensitivity to sunlight. Sunlight causes immediate and severe skin inflammation to exposed parts of the body (face, ears, vulva, pizzle and also flank in alpacas). The exposed areas become swollen and thickened. The ears will droop. This may be worsened by the animals rubbing. The skin will peel off and scabs from rubbing may increase the time it takes to heel.
Severely affected animals may show jaundice. Other significant symptoms in some animals are lesions affecting the lower urinary tract or oedema and ulceration of the bladder. FE can be so severe and stressing that it causes death.
Animals can survive and recover from the disease, but the effects of the acute disease on growth, body weight, wool and milk production can be dramatic. Even if the liver damage is insufficient to cause photosensitization there can still be “sub-clinical” effects on the production of meat, wool and milk. In any FE outbreak, many animals with liver damage show no clinical signs of disease, but analysis of blood enzymes do show that animals suffer from sub-clinical FE and may sustain significant liver damage, some quite severe (Towers 1978).
Animal deaths due to photosensitization can be substantially reduced by adequate protection of sensitised animals from sunlight. The provision of a highly nutritious diet for affected animals will promote recovery of their livers and may eventually return them to full productive capacity (Smith and O’Hara 1978).
Please note that P.chartarum is not the only organism producing a toxin that can cause liver damage and photosensitization. If you are planning to graze animals of high economic value on your property it may be necessary for a specialist from the Department of Agriculture to identify plants that may cause problems if ingested, and to determine if P.chartarum is present and does contain sporidesmin (Towers, 1995).
Toxic Conditions
Although FE occurs in temperate areas on mainly perennial ryegrass pastures, the fungus will grow on dead grass of other species and the disease may occur on pastures that contain no ryegrass at all (Hore 1960; Gardiner and Nairn 1962).
The fungus grows on the dead litter and the spores are carried up through the material by new grass growth, which is then consumed by the grazing animals. Conditions that promote the rapid growth of the fungus are warmth and humidity. The condition tends to occur in autumn after a hot, dry summer which provides sufficient dead, dry grass to serve as pasture litter. The fungus proliferates after a period of rain followed by several days of consistently warm weather (>15.5 C min.) with high relative humidity (>80 per cent) and light rain or heavy dews (Walsh 1966).
Managing Facial Eczema
There are a number of established procedures for avoiding and/or reducing the impact of FE and although all involve extra labour and financial expenditure, in most cases these costs are justified by the increased productivity and reduced animal losses that result.
Reducing Toxin Intakes
Monitoring Pastures
There are major differences in the spore counts found in different pastures due to variations in slope, shelter, exposure to sun and wind etc., there is the opportunity to assess the potential toxicity of pastures before they are grazed and then to graze the least dangerous pastures (MAF, 1981).
Spores of P.chartarum are readily recognisable and can be counted using relatively simple equipment i.e. microscope and blood cell counting slide (Chapman and di Menna 1981). For more information on spore counting see article – Facial Eczema – Predicting Danger Periods by Spore Counting published by Ministry of Agriculture and Fisheries New Zealand (copy held at Coolaroo). Spore counts on pasture samples are available through NSW Department of Agriculture laboratory at Rydalmere – contact Michael Priest.
There is no such thing as an unqualified “dangerous spore level”. The toxicity of a pasture at any one time depends on several factors.
- Numbers of spores
- Age of spores (old spores are less toxic)
- Grazing intensity (grazing down to base of pasture gives highest risk) – assessment of pasture is necessary, and the way the animals graze is important. If the pasture contains large quantities of dead leaf matter, even with low grazing intensity, the situation may be dangerous. This is especially the case with animals such as alpaca that tend to graze close to the ground regardless of the length of the pasture (Coolaroo experience).
- Prior exposure to spores gives high susceptibility
- Breed and species of animal
- Length of time over which high spore levels are present and consumed
Depending on the above factors the level of spores on pasture may prove to be toxic anywhere above 40 000 spores/gram of grass (wash count), and long term ingestion of low levels of spores may also lead to FE (MAF, 1991).
Spore numbers can vary within and between paddocks depending on the topography, aspect, altitude and previous management practices.
With spore counting and monitoring of grass minimum temperatures and rainfall to identify danger periods favouring rapid growth and sporulation ofP.chartarum, decisions can be made to reduce the risk of ingesting the toxic spores by altering grazing management and / or to implement other control methods such as spraying fungicides or dosing with zinc salts.
Zinc Oxide Dosing
Dosing animals with Zinc salts at a very high dose rates before and while they are exposed to sporidesmin can reduce the number of animals suffering liver damage, and the severity of the liver damage experienced by affected animals by 50- 80 per cent (Smith et al. 1977; Towers and Smith 1978).
There is a need for regular dosing and accurate dose rates which makes this method labour intensive.
Zinc Oxide Pasture Spraying
This method works best when the grazing area is small and pasture is moderately long to achieve a high pasture utilisation rate. Spraying is required weekly for sheep grazing. Dose rates may be difficult to calculate.
Zinc Sulphate In Drinking Water
This method works best for cattle, is not effective for sheep as they do not drink enough to get required dosage. This could also be the case for alpacas. This method is also labour intensive and the powder may be difficult to dissolve.
Zinc Rumen Capsule
A rumen capsule has been developed in New Zealand and is now available commercially for the controlled release of zinc oxide from the animals rumen for a six week period. Some research needs to be done to confirm whether it is possible to use these capsules successfully with Alpacas in Australia.
Breeding For Resistance
Tolerance to sporidesmin is strongly inherited. Gains can be made over a few years of concentrated selection.
Reducing Toxin Production
Fungicides
Spraying pasture with fungicides (e.g. Benlate ) in late January or early February (before spore numbers rise) reduces the growth of the fungus and lowers the numbers of spores formed (by about 55 – 65 percent) when weather conditions are dangerous. Pastures sprayed early remain safe for 4-6 weeks but need to be monitored during the danger periods. Rain should not reduce the effectiveness of the spray unless heavy rain occurs within a day or two of initial application. The approximate cost of using Benlate is $ .00 per hectare.
Farmers can spray all or only part of their farms. Individual management options, likelihood of severe outbreaks, economics and the terrain will decide the best strategy.
Grazing Management
Planned grazing can reduce the risks of FE in most situations.
Paddocks can be heavily grazed prior to the danger period and the animals placed onto these paddocks during a danger period and supplementary fed with quality Lucerne hay and high protein feed mixes with zinc salts incorporated (current Coolaroo strategy ). With this method it is important to ensure most of the dead litter on the surface of the ground is removed. This method will also be detrimental to desirable pasture species that require rotational grazing (my comment !!).
Ploughing a paddock and sowing a fodder crop prior to a danger period should provide safe grazing as there will little or no dead plant material present (my comment !!).
CONCLUSION
It may be concluded that FE is a disease which can cause considerable production losses, animal suffering and death. With careful management of pastures, monitoring of spore levels to identify the most dangerous paddocks, dosing of zinc salts to animals with some exposure and continual selection of animals showing some resistance, the disease problem can be controlled and production losses will be minimised.
For further information contact
Janie Hicks
Coolaroo Alpaca Stud
471 Woodlands Road, Mittagong 2575
E: janie@coolarooalpacas.com.au
T: 02 4878 5266
M: 0419 995 553