Long story short, my horse took a bite of my mum plant today. I pulled as much of it out of his mouth that I could. I was riding him at the time, so might have missed some. I didn't think too much of it and we continued to go on our trail ride, which took about 45 minutes. I got to thinking about it once I got home so I googled if mums are toxic to horses and they are. Does anybody know how toxic? Should I be concerned? He lives at my mom's, about 20 miles from my house, so I can't just check on him whenever. I was there for probably 45 minutes to an hour after we got back from the ride, grained him and hayed him and he seemed fine. Am I just worrying too much? Do they have to eat a large amount before it begins effecting them?