My mother is a vegetarian; I chose on my own to become vegetarian at thirteen, and when I was fifteen I became a vegan. I had many pets growing up, and I realized early on that they were all different to each other individually. I attribute this greatly to my decision. Actually, that is something that annoys me to this day; how people believe that animals are cut copies of each other, without their own unique personalities. Anyway.
I consider my dietary changes related to all three common reasons behind a typical person's choice to adopt a vegan lifestyle; ethics, health, and the environment. It's also a belief and ideal of mine (and I expect, many others who have adopted the vegan lifestyle) that no being should have to suffer; I'm an extremely empathetic person, seeing anything in pain just makes me feel horrendous.
Horse Racing: Nope, I can understand that some horses LOVE to race, and I don't have a problem with that as long as they are treated well (and retire happily), but I certainly do not support the industry. What really concerns me about horse racing, is that so many race horses are bred, and many them are not efficient enough to race professionally (or cannot race any longer), and thus, are cast aside and sent to the tin food factories. Also, I loathe the idea of animals as objects for human hedonism.
Pets: I'm kind of torn over this one. I support arguments for and against owning pets. It really irks me the amount of domesticated animals that are euthanized each year due to mass reproduction, abuse, abandonment, etc. related to human negligence. But I love my pets though, they are great companions, and I wouldn't give them up for the world...I'm pretty undecided on this one.
I let my pets eat meat. I think that dogs can be vegetarians as their diets seem to be diverse (my dog Maxwell loves vegetables!!!), unfortunately, I live at home, so he's really my parents' dog and so I don't really have a say in his diet (but that's okay, because his diet isn't solely meat). In terms of cats, I think they are truly carnivores (I'm yet to see a cat eat some greens), and should have a diet of meat; it seems so cruel otherwise.
Horse Riding: Kind of like the 'owning pets' argument. I can understand both sides of the argument. Really undecided.
Circuses: No. Just no. It just screams cruelty.
Animal abuse is sort of like morals in a sense; subjective to each individual's preference. Whilst some believe that horse riding is cruel, others won't be believe so. I think as long as an animal is healthy (both mentally and physically), and is not conveying or experiencing any kind of discomfort or pain when confronted with an action, then it isn't cruel (of course, this have exceptions - such as circus animals).