Equine Genetics

Since horses were first domesticated, thousands of years ago, we humans have been sculpting their genome through artificial selection. Where we notice qualities that we find desirable, like a cool temperament or great strength, we’ve bred in favour of those qualities – and in doing so produced a variety of animals, which have variously carried knights into battle, pulled enormous carts through city centres, and won prestigious racing events.

Though they didn’t know it, horse breeders throughout history have been steadily tweaking the genome of the animal – the instructions written into each cell which determine the size, shape and character of the eventual horse. In modern times, we know more about the equine genome than ever before – and the implications are exciting.

In 2003, the first human genome was successfully sequenced by the Human Genome Project, to widespread excitement and acclaim for the scientists involved. Just three years later, to a great deal less fanfare, the same breakthrough was made with the equine genome by the imaginatively-titled Horse Genome Project. Horse breeders across the world were understandably excited that they could finally see the shape of the genes begin manipulated.

Horse-racing is a business with an annual turnover in the billions of pounds, and the best quality racehorses can command six-figure stud fees. Naturally, if you’re going to spend such a sum, you’ll want to know that you’re getting quality. Equine genetics is being increasingly turned to as a way of guaranteeing that quality. A test is not particularly difficult to carry out; obtaining a testable sample of DNA just requires a sample of hair from the mane or tail – and so there’s no visit to the vet to worry about. With the help of one of the many testing companies which now exist, you’ll soon have access to the complete genome.

Perhaps unsurprisingly, horse breeders have been scouring the genome in search of the most desirable genes. In the process, some misconceptions and myths have arisen. Certain genes, for example, have acquired a mystique. The most notable among these is the so-called ‘speed gene’, which effects the production of myostatin, a hormone which controls the growth of new muscle tissue. While really, there’s no such thing as a gene that controls how fast a horse can run, it is possible to breed one that’s characterised as a sprinter.

In the motorsport industry, technological improvements developed to help F1 drivers win the world championship eventually find their way into the ordinary road cars you’ll find on driveways across the country. The same is true in the equestrian industry; while we might not all want to breed a thoroughbred racehorse, we can still take advantage of the technology that the thoroughbred industry has brought into existence.

We can, for example, use genetic testing to project what colour a horse’s coat will be, or how tall it might be when fully grown. In the case of height, two alleles have an impact: shorter horses have two A-bases; taller ones have two G-bases; those in the middle have one of each. Of course, these are general rules, and we must also consider the rest of the genome, and the environmental factors which undoubtedly play a role, too: but if you’re looking to breed a massive horse it makes sense to do so using a genome that’s proven to produce larger animals.

The same logic applies to coat colours. There are several genes involved in determining coat colour, but two stand out as especially significant: the so-called ‘extension gene’, and the ‘agouti’ gene, which respectively determine whether the coat is chestnut, and then whether the coat colour is uniform. A bay horse, for example, would come with a non-red extension gene and an agouti gene which causes the black pigment to be present only at the animal’s extremities.

Of course, among the most useful applications of the genetic screening technology is its ability to identify genes which carry disease. This means that we can not only identify diseases present in the horses themselves, but breed those horses in order to remove the disease in question from the next generation. Naturally, disease eradication isn’t the only consideration when breeding – and so especially prevalent genetic conditions might not be so easily destroyed. Nevertheless, it remains an exciting time in the world of horse-breeding.

The ultimate objective here should be that genetic diseases are entirely eradicated. And there’s no reason why this can’t be achieved; great breakthroughs have already been made at reducing the number of foals suffering from foal immunodeficiency syndrome. We might yet see similar progress made with respect to other diseases, like hyperkaliaemic periodic paralysis. This disease is often found in American Quarter Horses, but with the help of widespread genetic testing, we’re better able than ever to guard against it. The condition has been traced back to a single stallion, who while never displaying any symptoms of the condition himself, has nonetheless passed the defective gene which causes the condition down to all of his progeny. With the help of genetic testing, who knows what other diseases might be identified and one day eliminated?

So what’s next for the world of genetic testing? Despite the squeamishness that some may feel toward the practice, its adoption by breeders looks to be irreversible – and we’re sure to yield considerable benefits from the practice. A horse that suffers from an avoidable genetic condition is a senseless waste – particularly now that we’ve a means of avoiding such suffering.

It’s a very exciting time to be a horse breeder. We’ll soon be able to see precisely which stallions are carrying the desirable genes – even if those stallions themselves might not be as impressive as their contemporaries. With a new pool of stallions becoming suddenly desirable, we might yet see downward pressure on stud fees – which can only be good news for horse breeders. In the near future, this technology looks set to afford us the ability to sculpt the equine genome in a way that our ancestors could have only dreamed of.

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