The cow, the horse, and the sheep (after Loyd)

Here is a twist to a well known problem which, to my surprise, seems not to have appeared before.

A farmer has a field, a cow, a horse, and a sheep. All three animals together can graze the field bare in two days, but the cow and the horse without the sheep would take three days, the cow and the sheep would take four days, and the horse and the sheep six days. How long would it take each animal to graze the field bare on its own?