Choosing the Right Stallion for Your Mare

Picking a stallion is one of the most exciting parts of breeding a mare, but it is also a decision worth putting some homework into. A great stallion is not automatically the right stallion for every mare.

The goal should be to find a stallion that complements what your mare already does well while hopefully improving the places where she could use a little help.

Start by taking an honest look at your mare. What do you love about her and hope she passes on? Maybe she has great feet, plenty of bone, a good mind, a strong hip, a nice way of moving, or the natural ability you want in another horse.

Then look just as closely at the things you would like to improve. Maybe you would like more size, a shorter back, better feet, more substance, a different type of movement, or a quieter disposition.

No horse is perfect. The idea is simply to avoid doubling up on the same weaknesses.

If your mare has a trait you would like to change, look closely at that trait in the stallion and in the horses he is producing. A stallion can look incredible himself and still not consistently pass those same qualities on. If he has enough offspring on the ground, pay attention to what keeps showing up across different mares.

The same goes for temperament. Photos can show you conformation, but they cannot tell you what a stallion is like to handle every day, how trainable he was as a young horse, or what kind of minds his offspring tend to have. Those are good questions to ask the people who know him and the people riding his offspring.

It also helps to know exactly what you are trying to raise. The stallion you choose for a serious performance prospect might not be the same stallion you would pick if you are trying to raise a quiet ranch horse or a useful all around horse. Pedigree, earnings, and accomplishments can all be helpful information, but the cross still needs to make sense for the mare and for what you hope to produce.

Genetic Testing Should Be Part of the Decision

Genetic disease testing is another part of choosing a stallion that deserves more attention than simply seeing the words “panel tested.”

You also need to understand what the results mean.

Genetic diseases can be inherited in different ways. Two of the most important terms for breeders to understand are dominant and recessive.

With a dominant disease, a horse only needs to inherit one copy of the disease variant for it to potentially affect that horse.

PSSM1 is a good example. It is an autosomal dominant condition. A horse with one copy of the PSSM1 variant can develop symptoms of the disease and has a 50 percent chance of passing that variant to each foal. A horse with two copies will pass the variant to every foal.

That is very different from a recessive condition.

With a recessive disease such as HERDA, a horse generally needs to inherit two copies, one from each parent, to be affected. A horse with only one HERDA variant is considered a carrier and is not expected to develop HERDA itself. If two HERDA carriers are bred together, however, there is a 25 percent chance with each breeding of producing an affected foal.

This is why simply saying a horse “has one copy” does not tell you enough. You need to know whether the disease is dominant or recessive.

For a dominant condition such as PSSM1, one copy is not just a carrier status. That horse has the disease-associated variant, may show symptoms, and can pass it directly to its offspring. UC Davis reports that an N/PSSM1 horse has a 50 percent chance of transmitting the variant to each foal.

HYPP is another example where one copy can affect the horse. Horses with one HYPP variant can experience episodes of muscle tremors or paralysis and can pass the variant to approximately half of their offspring. Malignant Hyperthermia is also inherited dominantly, so one copy can result in an affected horse and can be passed to offspring.

MYHM works a little differently and is described as codominant with variable penetrance, but a horse with one copy may still develop disease and has a 50 percent chance of passing the variant to its offspring.

For many breeders, this is a good reason to choose a stallion that tests clear for dominant disease variants when a clear option is available. Even if the stallion himself has never shown obvious symptoms, breeding him can pass the variant into the next generation.

Recessive conditions require a little more nuance. Breeding a carrier of a recessive disease to a genetically clear horse will not produce an affected foal for that particular condition, although some of the foals may become carriers themselves. For HERDA, for example, a carrier bred to a clear horse is expected to produce no affected foals, but about half may inherit the variant.

Some breeders are comfortable making those crosses carefully. Others prefer to breed clear to clear so they are not continuing to pass the variant through future generations.

Either way, the mare needs to be tested too.

A stallion's genetic panel only tells you half of the story. Knowing the status of both horses allows you to understand what the cross can potentially produce before you make it.

Color Can Come Later

There is nothing wrong with hoping for a buckskin, palomino, roan, or whatever color you love. Color genetics are part of the fun of breeding horses.

But first, make sure you like the horse you are trying to make.

Color cannot make up for poor feet, a difficult mind, unsuitable conformation, or knowingly producing a foal at risk for a preventable inherited disease.

At the end of the day, there is no breeding cross that guarantees exactly what you are going to get. Genetics can surprise you even when both parents are outstanding individuals.

But you can stack the odds in your favor.

Know your mare. Study the stallion and his offspring. Look at both sides of the pedigree. Understand the genetic panel instead of simply checking that one was done.

Then choose the stallion because he truly complements your mare and gives you the best chance of raising the horse you were hoping for.