Facial Eczema, what is it and what it costs the sheep farmer

The disease

Facial eczema is caused by the ingestion of sporidesmin, a potent mycotoxin produced by the fungus Pithomyces chartarum that grows on dead leaf litter in the late summer and early autumn.

Not all isolates of Pithomyces produce sporidesmin, however 95% of NZ isolates do versus 2% in Brazil. Aren’t we the lucky country?

This fungus requires 100% humidity and temperatures in the range on 10-30 C for sporulation.

Sporidesmin primarily damages the liver, especially the bile duct cells, where it causes an obstructive jaundice, resulting in the degradation products of chlorophyll accumulating in the blood.

This accumulation of chlorophyll byproducts results in secondary photosensitivity, due to UV reactions with these byproducts and the release of histamine. This outward reaction to sporidesmin only happens on a proportion of animals, and only on those animals that have light coloured skin.

The primary damage is to the liver, and it is this liver damage that gives rise to most of the production losses both short term and long term.

Spore counting and what it means.

Spore counting pastures over periods of risk can alert you to increasing spore counts. Farmers that have had problems in the past will know what areas of their farm will be affect first.

 Interpretation of these spore counts would be in relation to the time of year and weather factors.

One off spore counts of 100,000 or more are dangerous but spore counts of 40,000 over a number of days can also be significant, especially when animals are grazing close to the ground.

FE what does it cost you

When we have seen severe outbreaks of FE the costs have been obvious. In the early 90’s some farmers in this district lost a third of their ewes and had to send another third to the works.

Some other years scanning percentages have been reduced by 20%, the first cycle conception rate was reduced and the empty rate was increased 4-6%. These are district averages, so some farmers would be affected more than others.

The simple costing on this would be greater than

2000 ewes less 20% of lambs @ $120 each = $48000

2000 ewes less 4% of lambs    @$120 each = $9600

Of course losses will be greater than this because we have to take into account that later born lambs stay longer on the farm, Hogget mating may need to be called off, some ewes will die over winter etc.

Zinc Supplementation

Zinc is very effective in controlling the harmful effects of sporidesmin. Zinc acts by forming a complex with sporidesmin, eliminating its ability to form oxygen free radicals which are responsible for its toxicity.

In sheep the only practicable method of applying zinc is in the form of a bolus

The cost of this is not cheap, and we see lots of farmers wrestle with this every year.

To treat 2000 ewes will cost about $7300 applied.

Ramguard- breeding for resistance.

This has to be one of the long term fixes. Genetic gains of 2% per year have been seen with ram breeders.

Of course commercial farmers can get better gains than this by buying rams from breeders that have been on this course for some time.

By Richard Atkinson

Atkinson & Associates Veterinary Services

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