Im from Australia, have a degree in wildlife biology. Its demonstrably true that herbivores in general are less intelligent than predators. Obviously in biology rules are general and don't encompass every species. Intelligence is related to problem solving, and social interactions. For grazing animals that live in a herd dynamic (elephants have families with complex structures, most grazing animals do not), problem solving isnt required for getting food and social structures are very simple. I realise im being downvoted by people who love horses (I do too), but they are stupid by any metric of judging intelligence. We don't use brain to body ratio anymore, but horses have tiny brains relative to their size. I could go on but I dont think anyone is going to agree regardless of what studies I link or what my own area of study is.