If you can't find anything better, the critical rules of thumb for any short term rental that it is for a specified period of less than 365 days ie there is some period in the year where the animals aren't there, to prevent any rights being acquired, also when the rent is paid, what happens if the rent isn't paid or the animals aren't moved. And the notice period on both sides, any obligations re fencing to keep the stock in, watering and feeding eg hay if in the winter.
With sheep you often rent the land out either for the winter or for the summer as the sheep would normally need fresh ground at least that often,and it will stop the land becoming sheep sick.
The local land agents/solicitors will be able to draw something up for a fee but someone may have a sample you can cannibalise.