I am a huge fan of the late Andre Norton. This book was one of the first of her Witch World series I read, back in the 1980s. That book is currently packed in a box, so I decide to get the ebook.
It involves a young man named named Kethan. His mother and a wise woman have conspired to birth a son who will be a powerful ruler under their control. To their chagrin, a daughter is born (women can't rule). So the switch the girl for a boy child at birth (Kethan). Kethan never seems to quite fit in. One day a merchant visits their keep, and he is presented with a belt with a buckle made of Jargoon. The belt is made from the pelt of a pard and the buckle shaped into a pard's head.
He finds that he can use this to change into a big cat. However, he still doesn't know how to control his abilities, and he has other problems. His rival wants to use his shape changing ability as an excuse to kill him. For his mother and the wise woman, this gives him a means of freedom they are determined to deny him.