I think most relevant law is "HAYVAN ISLAHI KANUNU" (animal care law, law ID 4631, enact date 28/Feb/2001, Release date 10.03.2001). You may like to check it out but I'm not sure if you can find an English translation. It is hard to find even the law itself in Turkish. If you are not Turkish citizen, you may also like to check if another law regarding foreign status forbids foreigners to work in this business or not. I don't think so but this field is not my expertise so I can't advise. Lastly you may like to check whether the location of the stable you like to set up is open for foreign purchase or not if you are planning to purchase it.