There's no reason to think this would have worked. To quote Jared Diamond, only 14 of 148 large herbivorous mammals have ever been domesticated because they ne

There's no reason to think this would have worked. To quote Jared Diamond, only 14 of 148 large herbivorous mammals have ever been domesticated because they need very specific traits to be domesticable - pleasant disposition being one of them that hippos lack. Is there any evidence that humans have ever succeeded in domesticating hippos?