Just to add to that last post

After a little more digging it appears that cows CAN graze on land that a Right of Way passes through BUT this does not mention Bridleways just a Right of way!.

See here (its about 2/3 rds of the way down the page).

http://www.imba.org.uk/index.php?page=PRoW_FAQs

"Which cattle may graze fields which are crossed by rights of way ?

All cows are OK - although be wary of cows with calves
All beef bulls such as Herefords or Aberdeen Angus are OK as they are normally quite placid .

The law makes it illegal to have a dairy bull such as a Jersey, Guernsey or Fresian bull in a field with a right of way, because they can be very aggressive."

Hope this also helps?