Hands Off Hartlebury Common

"The toxic nature of oaks is irrelevant to the debate. The site is to be lightly grazed by cattle who are not suseptable to an oaks toxin."

And from the The cattle site.com

Clinical Signs

Sudden death can occur (although poisoning generally occurs over a period days)
Constipation initially, followed by black watery diarrhoea.
Depression and loss of appetite
Straining to pass faeces and urinate is very common
Weakening, collapse and death (usually within seven days of the onset of signs)
The animals have a normal temperature in most cases
Acorns can cause birth defects if eaten in sufficient quantities by pregnant cattle Acorns contain gallotannin. In the rumen, gallotannin is broken down to gallic acid and tannic acid. Tannic acid causes ulcerations in the mouth, the oesophagus, and the rest of the intestines. It also damages the kidneys, and it is kidney failure which causes most of the death associated with acorn poisoning. Acorn poisoning will generally affect only a few animals in the herd, as acorn poisoning only occurs if animals eat large amounts of acorns (which will only occur in cattle which develop a taste for them). As tannins concentrate in milk fast-growing calves on heavy-milking dams will often be the first animals to show signs.

I know who I would rather believe