Is it dangerous if a small bull tries to mate with a Belgian mare and will the mare even let that much smaller animal mount her?

Answer 1

A bull is a bovine and a mare is a horse. Your question makes no sense.

Another Answer:

It depends on what part of the word "dangerous" you are referring to. Are you asking is it dangerous for the mare or dangerous for the bull?

From the gist that I'm getting from the question asked, I have to say yes, especially for the bull, as he could get injured if he keeps trying to breed her. Please do these two animals a favour by completely separating them from each other.

Additionally, though I have no idea what kind of other animals you have on your farm, if you have the bull because you only have one or two cows, do yourself (and even the mare) a favour by considering selling him. That bull is most likely attempting to mount the mare because he is sexually frustrated that he doesn't have a large number of cows to breed with. One bull can be used to cover from 10 to 50 cows or heifers in one breeding season: this means that cattle are polygamous, not mono- nor bigamous. If he isn't given the opportunity to release his pent-up sexual energy by being with his girls for a few months to breed as many of them as he can in that period, then he will find other ways to release his frustration and attempt to breed other animals like your mare, or break out of his enclosure and go in search of other cows that are requesting his services.

Bulls can also be very dangerous, and cost more (especially in feed and mineral) to keep than it costs to keep a couple of cows around and breed them via AI. (AI is an alternative and completely harmless to having a bull around, especially if you only have one or two cows around.) It's also not worth anything by keeping a bull around as a "pet" (bulls are actually the worst kind of pet you can have) if you have no cows to speak of and if he's causing more trouble than he's worth. If that is the case, then consider selling him to someone who can make better use of him.

If you can't or don't want to get rid of the bull for whatever reason you have, be it that you're keeping him because you are some sort of farm sanctuary, or you cannot get any local artificial insemination technicians out to provide regular breeding services to your cow[s] (or don't wish to have your cows serviced via AI because you believe it "cruel" and "unnatural," the former which is not and the latter is), then keep the bull and your horse separate from each other permanently. I would also strongly recommend you consider the future of this bull from what I mentioned to you above if he is causing more trouble than just trying to perform interspecies coitus.

Answer 2

It is potentially dangerous for either animal. The bull could easily be injured if the mare kicks him and the mare could be injured if the bull butts or gores (if he has horns) her if he becomes frustrated. Generally this type of inter species interaction is rare. If by some freak chance the bull actually achieves intromission his penis could actually be broken due to the considerable difference in size between the two animals.