According to Fungus threat to dairy cows soars, by Richard Woodd:

The facial eczema threat to dairy herds has soared to critical levels in parts of Taranaki this week in perfect growing conditions.

Facial eczema is a disease which causes lowered production and sometimes death from liver damage. Fungal spores produced by the fungus Pithomyces chartarum growing on pasture produce a toxin which when ingested by cattle damage the liver and bile ducts.

The damaged liver cannot rid the body of wastes and a breakdown product of chlorophyll builds up in the body causing sensitivity to sunlight, which in turn causes inflammation of the skin. Exposed unpigmented or thin skin thickens and peels.

Pithomyces spores (courtesy of Bryce Kendrick and Mycolog)

That is a strange chain of events linking a fungus, the environment, and cow faces. Pithomyces is a genus of dematiaceous conidial fungi. The toxin in question is called sporidesmin.

Kikuyu Poisoning

In not too far away (from New Zealand) New South Wales, a fungus is also causing worry. It apparently isn’t the same one that causes the facial eczema, since the article Grass fungus can kill cattle, from the Tweed Daily News states:

“The fungus produces a toxin that irritates the third stomach, causing it to fail to perform its normal job of absorbing fluid,” he <a veterinarian> said.

“This causes a build-up of water in the main stomach or rumen, giving the cattle a bloated appearance. The weight of this fluid can be too much for the heart and lungs to bear.”

Strangely, this ailment is called “Kikuyu poisoning,” named after the grass the cows eat, even though the grass is actually good fodder, and it is only after a wet spell that the fungus grows on the grass causing it to become toxic.