The Food Standards Agency said it was the first known case of sweet potato poisoning in animals reported in Britain.
The vegetable, long popular in the Americas, parts of the Pacific and China, is rapidly gaining popularity as a food in this country and the Food Standards Agency recommends it as a source of vitamin C.
The deaths on an unnamed farm in East Anglia happened over four days among a group of 15 Limousin cross beef cattle fed 7kg (15lb) of sweet potatoes each a day for more than a week in September. The tubers had been bought as animal feed because bruising made them unfit for humans.
Damaged vegetables can develop fungi that produce dangerous toxins, according to a letter alerting farm vets to the danger in the Veterinary Record. The disease was first reported in the United States and Japan in the 1920s.
Government vets have urged farmers to limit sweet potato use despite its attractiveness as a cheap high-energy food for cattle.
The agency said it was not aware of any cases of sweet potato poisoning in humans similar to that caused by mould damage in animals.
But the FSA's advice is that all varieties of potato should be stored in a cool, dark and dry place so there is less chance of their developing natural toxins which can cause abdominal pain, vomiting and diarrhoea.
"But glycoalkaloid poisoning is extremely rare, even though potatoes are eaten in very large amounts in many countries," it said.