Recent strong winds have blown these leaves into my place. It is spring here so I assume it's from a deciduous tree that holds its dead leaves through winter. Some trees are toxic to sheep and I've already had a close call when fresh maple leaves were blown into my place during a storm.
These leaves could have come from as far as 6kms away.

Looks like some sort of oak, possibly this:

sessile oak (Quercus petraea)

Thank you. Most oaks are toxic to sheep so I will try to gather up as many of these leaves as I can and dispose of them.

You might want to save yourself a lot work by doing a little more research first: is it only live green oak leaves that are toxic for sheep or the dried brown ones also? Chemicals in the two forms are vastly different, and maybe you won't need to worry about dried brown oak leaves.

They are less toxic when brown and dry but are still a hazard.