Also meant to mention Patonio, cowboy song and Widdecombe Fair which is about Tam Pierce's gray mare which has a rural base though not about agriculture.

Another suggestion that might be helpful is on the main page that lists all threads there is a box beside the word "filter". If you enter the word "mule" or "horse" in the box and the select "All" in the Age box and then Refresh you will find all that has been put into Mudcat on this subject.