A cattle disease so rare that most veterinarians have seen it only in textbooks has been found on six Southland dairy farms.
The disease - gangrenous ergotism - was discovered on a dairy property by Invercargill Veterinary Services vet Merlyn Hay and confirmed by diagnosis at Gribbles Veterinary Pathology lab at
Invermay.
The disease has since been found in five more herds belonging to Veterinary Services' clients, and other cases have apparently been diagnosed in South Otago.
The disease is caused by a fungal toxin found in ryegrass seedhead.
It results in severe hind limb lameness, which progresses to gangrene and severe sloughing of the skin and tissues around the hoof.
Merlyn Hay said the disease was extremely rare.
But a hot, dry summer followed by a cold, wet winter had resulted in ideal conditions for the development of the fungus.
"Normally it is not warm enough for the fungus to grow."
Cattle ingest the toxin through silage or hay bales containing infected seedheads.
Merlyn Hay was involved in finding the disease on all six affected farms and believed a lot of other cases may have gone undiagnosed.
"It's really unusual and often seen only in textbooks.
"There is no treatment and cows have to be euthanased."
She said more than 100 cows could have been affected by the disease.
Gribbles' diagnosis had found ergotised ryegrass in two of three outbreaks checked.
In all other cases, all of the suspect feed had been fed out before the disease was confirmed.
Merlyn Hay recommended that even though the disease might not appear again for many seasons, silage and hay should be cut earlier to ensure higher quality and low levels of seedhead.
- NZPA
