I never bred a two YO mare, and never would. In past, I have bred them at three, but on reflection, if I were to breed again, I would wait until 4 or better, 5. I would be interested in hearing the source and scientific backing for whether the pelvis 'fuses' at 4, and how that has been proven to have an adverse impact upon delivery. Honestly, I can't really accept the reasoning that one should 'get a mare into production' as early in her life as possible because at maturity, she 'might' prove to be unsuitable as a broodmare....that makes NO sense to me; to me, the genuinely 'GOOD' broodmares are ones who would be able to fulfill that purpose well and without issue in every way, under optimum(for THEIR well-being) circumstances. If a mare, upon GENUINE MATURITY, has 'too-narrow' a pelvic opening, what makes you think she won't likely pass that drawback along?? Seems to me like a REALLY good reason to WAIT until full official(generally, defined as a full 5 years/60 months of age) physical maturity to breed a mare, to me....
I leased out a mare some years ago(she was older than two)to be used for breeding; she had to have surgical intervention when the time came. According to the terms of the lease, the lessor did cover all vet costs, and she survived. Because the university vets told them she had 'too-narrow' a pelvis, they returned her 'early', understandably not wishing to attempt breeding her again (to which I wholeheartedly agreed, of course!) I later sold her locally, at a very reasonable price, with a firm agreement that she never again be bred, primarily for her safety--but also, because of the above-mentioned reason.
And-as long as we are mentioning the terrible 'things done too young' to horses(and therefore, very dangerous to their well-being)
-- let's not forget things like 2 YO cutting and reining futurities, and ads on the horse-for-sale websites showing people riding horses(often, gaited breeds, for some strange reason) well UNDER age two, complete with full-sized western saddles and full-sized IDIOTS on board...etc.,etc., etc. There is, pitiful to have to say, PLENTY of lack of consideration for the well-being of the animal to go around.....I think we can all 'guess' what is more important to the people involved....
Unfortunately, it has been a 'historic' practice of MANY who've bred miniature horses to breed mares ASAP-meaning at age two or younger.(The first mini mare I bought, still here and happy at 26, had a spring foal at side when I bought her, yet didn't turn 3 until October of that year--it was SOP back then.) Can't help but think it was about the money; why else?--especially back in the 'glory days' of the late seventies, and eighties, when nearly anything brought a relatively high price. Those days are past, but some still follow those kind of practices; I have to wonder why?
Margo