Does a draft mare have too large a reproductive tract for a bull if they mate?

Answer 1

Physiologically speaking, the reproductive tract differences between a mare and a cow (a mature female bovine) are not all that different from each other if we don't go past the cervix. Both have the vulva and vagina situated underneath the tail below the anus, and both have to hold their tail aside to accept the penis of the stallion and bull, respectively, in order to successfully conceive. Thus the question is not about whether a mare's vagina is too large for a bull, it's rather if the bull can "do the job."

You see, the morphological differences in size and situation of the reproductive organs between a stallion and a bull are much more different than that of a cow and a mare. Both the stallion and bull are endowed with similar penis length, however the stallion is larger in terms of girth. The penis of the bull is pointed, and is situated on the belly almost exactly between the fore- and hind-quarters. With a much more blunted and boulbous end and situated between the hind legs close to the testes, the stallion's penis is Nature's design to encourage the mare to go into orgasm (via a bit of thrusting "action") and accept the semen the stallion ejaculates into her vagina. With a bull, however, simply the warm environment of the cow's vagina--coupled with a couple good thrusts--is enough to send him into orgasm and encourage ejaculation. With this in mind (however "disturbing" you may think it is at this point), though the bull may recieve some level of pleasure from the warmth of the mare's vagina, the mare isn't going to feel much the same from the lack of girth the bull has to offer. Distinctive behavioural differences between how cattle and horses perform their ritual courtship or "foreplay" before the actual mating commences are also worth mentioning at this point, and which ultimately determine if the mare, in the end, will accept the amourous bull.

A mare must be receptive or in estrus (or "heat") before she can accept a mate. If she's not in standing heat, she will put up a fight in the form of biting and kicking before she'll let any suitor mount her. A cow will move away from the bull when he tries to mount, and may come around to butt him with her head. A butt from a cow's head will hurt less than a solid bite or nasty kick from a frisky mare to the bull and may or will discourage him from attempting to mate with the mare again, if he so dares. To add, a mare often will not come into estrus in the presence of a bull; there's a much higher chance of her showing heat when a stallion is sniffing-distance away and when she has not been around any stallion for some time. Cows will come in heat regardless if a bull is present or not.

If the bull is very daring (and a bit stupid, one might add) and refuses to quit his attempts to court and breed with the mare, he might be able to mate with her, if he's big enough to mount such a large horse and if she's in standing heat in his presence, which, as implied above, may be a rare event indeed. However, with the odds in the mare's favour, such matings are improbable and next to impossible. A bull might end up getting injured in the process by the mare's less than eloquent attitude towards her would-be bovine boyfriend before he even has a hope of performing interspecies mating with her.

Thus, when all is said and done, it's doubtful that such a mating would end up making both the bull or the mare very satisfied with such "attempted" endeavours, more on the bull's part than the mare's. Also, in terms of the question asked, size of the mare's reproductive tract is far more irrelevant than the morphological differences between the reproductive organs of the stallion and the bull and differences in courting behaviour.