haha, you know that simply hasn't come up till now.
above all, i think things should be FUNNY, ADORABLE, or perhaps cool, but that's kinda hard to do with cartoon scaled down horses.
safe for work is what i was shooting for, but a really lax kind of safe for work. As long as it isn't straight up porn, go for it.
Pretty much if it doesn't have horsecock, horsevagina,horseanus, or horsetits in it, you're good.