Facial eczema in sheep
Facial Eczema is a fungal disease that causes lowered production, photosensitivity and/or death due to liver injury.
For growth and formation of toxic fungal spores on pasture, warm and wet conditions during the day and night in the summer and autumn are required.
The fungal spores produce a toxin, sporidesmin, which when ingested causes liver injury and facial eczema (FE).
We often judge a bad FE year on the number of animals with visible symptoms, but the greater concern is the number of subclinically affected sheep (those with no visible symptoms but with liver damage) in a flock. If 5% of sheep show FE signs, it is likely that 50% of the flock will have subclinical FE!
An outbreak causing moderate liver damage in sheep can produce
- reduced fertility and fecundity
- reduced lifetime productivity in hoggets (up to 25 %)
- reduced growth rates in lambs and hoggets*
- increased culling of ewes (up to 12 % higher)
- deaths in ewes in winter and around lambing
(*One study from Agrisearch Ruakura showed the loss in weight of lambs weaned could be as high as 13%).
All these losses can be suffered in a flock with just a handful of sheep showing visible symptoms.
The key to preventing FE is to initially monitor the weather conditions and regional spore counts. It is then prudent to be doing spore counts on your own property once the regional spore counts get to about 20,000 spores per gm.
Strategies for the prevention of FE e.g. oral Zinc bolus application, such as The Time Capsule® or Face-Guard™ boluses, or spraying the pasture with a suitable fungicide, should be implemented as soon as spore counts on your property begin to rise or when suitable weather conditions occur.
Like all FE control methods, zinc dosing is not 100% effective. Therefore, breeding for FE tolerance, and applying good grazing management, are the best options long-term.
When spore counts are increasing and conditions are suitable for FE, practice lax grazing to ensure that livestock are not grazing to base levels on the pasture where spore counts are highest. Grazing sheep on forage crops and alternative pastures, e.g. chicory, plantain, legumes and tall fescue, will also reduce the risk significantly. Pasture spore counting will help you avoid known “hot spots” and identify “safe” paddocks.
If stock are being grazed off the property in a high risk area, ensure that adequate control measures are in place for these animals as well.