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Can Large Stallions Breed Small Mares?

For those breeding horses, there is quite a lot to consider when selecting a stallion to pare up with a mare. Breed and characteristics, of course, play a role, but so does size, particularly as foaling can be delicate and complicated at times.

The last thing any horse breeder wants to do is place their mare at risk. While there is not much information out there about what size difference is suitable for breeding, many equine forums detail the experiences of those who have been paring horses for years.

In this post, I’ve compiled information from various sources detailing their first-hand experience of breeding large stallions to smaller mares.

Both the size of the stallion and the size and birthing girth of the mare will determine the eventual proportions of the foal, particularly if the mare is still a maiden. While paring horses of different breeds and sizes is not unheard of, some considerations need to be explored.

This article answers the question of large stallions breeding smaller mares, specifically looking at if a male horse can be too big for a female horse and if a mare can suffer harm due to inappropriate breeding practices.

I’ll also look at the size difference most breeders agree is appropriate and other physical build factors that come into play.

Can Large Stallions Breed Small Mares?

Throughout history, many a large stallion has bred with a smaller mare. However, this practice is not always advisable.

Generally speaking, the acceptable size difference between a breeding pair is no more than one hand high and up to two hands at a push, but this is a guideline and not a hard and fast rule.

The greater determiner of a successful pregnancy is the width and stockiness of a mare, which will, by default, have an impact on the size of her uterus.

With 5% of all horse births experiencing complications, it follows that any horse breeder will want to give their mare the greatest possible chance of a successful pregnancy.

When it comes to selecting a stallion to pare with your female, you may want to consider his size as well as her girth. A slender, taller stallion can mate well with a shorter but stockier and wider mare. A strong, muscular stallion and a petite mare, on the other hand, may not fare as well.

Overall, it is commonly agreed that a big size difference between a stallion and a mare is not worth the risk of birth complications.

There is a strong chance that the subsequent foal may take after the stallion and grow too big inside the mare’s uterus, making birth difficult or resulting in a stillborn foal.

Large stallions can also unintentionally harm mares in other ways, which we will look at in the following sections.

Can A Stallion Be Too Big For A Mare?

A stallion can indeed be too big for a mare. The greatest risk, in this regard, is that any foals resulting from breeding will adopt the father’s genes and become too big for the mare’s uterus.

In addition to this, stallions that are too tall and heavy can harm small mares during the mating process by placing too much weight on their backs, or alternatively, because their reproductive organs are incompatible in size.

Furthermore, issues may arise if the mare is not in prime condition or is still too immature for breeding.

While the general consensus is that one to two hands larger is appropriate for a stallion and mare paring, height is not the only factor to be considered. Some horses are stockier and more muscular than others, and of course, some will be wider and heavier.

Bone density also differs between horse breeds, and stallions with heavy-set bones should not be paired with much smaller, more delicate mares. For example, one shouldn’t pair a cart-horse with an Arabian horse.

Size and compatibility become increasingly important to consider depending on whether the mare in question is a maiden.

Young mares who have yet to foal are at higher risk of developing health issues than broodmares, and for this reason, their breeding stallions should be chosen with care. The first foal a maiden mare delivers is usually her smallest, as her body is adjusting.

A very large foal can make the birth process risky.

Can A Large Stallion Harm A Small Mare When Breeding?

Unfortunately, large stallions can unintentionally harm small mares when breeding, particularly if they are strong and heavy-set. For small mares, there is also the risk of tearing and wounding if they cannot accommodate a much bigger stallion’s sexual organ.

To prevent this, it is better to breed with mares and stallions similar in size and stature, thereby lowering the risk of injury.

While horses are relatively hardy, live cover (as opposed to artificial insemination) can be a very physical process. Big stallions can accidentally hurt small mares during mating by putting too much weight on their back legs or by causing uterine or vaginal tears.

To avoid this, make sure you consult a breeder or vet before allowing your mare to breed.

Indeed, should your mare successfully pare with a larger stallion and fall pregnant, it is also good practice to involve your vet for the duration of the pregnancy.

This way, they can be on the lookout for any potential size or health issues with the foal and be on standby to assist should there be problems during birthing.


Breeding can be exciting for horse owners, but it can also be nerve-wracking. Pregnancy can be risky, especially for smaller mares, so it’s good to put preventative measures in place to ensure all goes smoothly. Part of this is selecting the right stallion. With large stallions breeding small mares, always make sure your vet is present and in the know. If there is a significant size difference between the animals, err on the side of caution and opt for a different mate.