Cows from almost all of Guernsey's farms have been struck by a respiratory virus that has left them unable to eat.
Bovine Respiratory Virus is common in the UK but has never been seen in Guernsey before, meaning its impact is widespread and severe.
The island's leading vet does not know how the virus travelled to Guernsey, and said it is possible but unlikely that it came from sheep or goats imported from the UK.
David Chamberlain, Guernsey States Veterinary Officer, said: "It causes so much damage to the lungs it makes them almost go to swiss cheese.
"Syncytial viruses join up cells and make bubbles, that damages the cells and the lungs can even leak air and that air travels north in the body and eventually ends up under the skin at the back.
"That's when you get that strange bubble wrap sound and appearance on the back of the cow."
Mr Chamberlain said most of the island's farms have been affected, and only a few have escaped so far.
When the cows catch the virus they stop eating, causing their milk production to drop.
Whilst cow flu comes to Guernsey every year, this virus is so severe that it can be fatal to some cows when they develop consistent coughs and stop eating.
Many farmers have seen a drop in milk yields over the past few weeks, but it has not affected production levels at Guernsey Dairy due to backup stock.
There is no danger of the virus being passed on to humans, and Mr Chamberlain said most of the affected cows are now recovering.
It is hoped that Guernsey cows will build up immunity to the virus now they have been exposed to it.
Mr Chamberlain is recommending farmers to consider vaccinating their calves to protect the next generation to try and prevent an outbreak on this scale from happening again.