Have you ever wondered where your horse’s supernatural jumping ability comes from? Does Big Star get it from his mamma? What about his brother from another mother, Ian Millar’s Star Power? Breeders say it’s in their bloodlines, while other horse people say it’s a combination of factors and a little bit of luck. I’m well into my MSc Applied Equine Science, examining the genetics of show jumpers to find out if a specific gene, myostatin contributes to show jumping performance in the elite horse.
Myostatin is a gene that is present in all mammals, responsible for regulating muscle mass. Scientists have already studied what effect mutations have on dogs, mice, cattle and horses. It works to regulate muscle mass and development. Because it’s a negative regulator, when the gene is switched on it stops increases in muscle mass.
Look what happens when this whippet has a mutation on both of his myostatin genes. When both pairs of the gene are mutated we get this massive, muscly dog because there is no signal to turn off muscle development. Fortunately, when both pairs are mutated in the horse, the appearance is quite different.
In the horse, myostatin mutations have been isolated in the Thoroughbred racehorse by a group in Ireland. Their work identified three possible genetic combinations or ‘genotypes’, C:C, C:T and T:T. They call it the ‘Speed Gene’ test because it has been found to accurately predict whether the horse will be a sprinter (C:C), middle distance (C:T) or long distance/stayer (T:T). The test does not guarantee that the horse will win at that distance, however, because racing ability is a ‘polygenic’ trait – meaning there are a lot of different factors, both environmental and intrinsic, that contribute to the horse’s success.
Researchers all over the world have compared racehorse winnings to their genotype with the conclusion that myostatin has the greatest effect on distance in many different populations of Thoroughbreds. Interestingly, the C:T genotype, with only one mutated gene, is a bit more flexible, with both sprinting and long distance ability. The gene also changes in response to exercise. In both humans and horses, myostatin seems to decrease in response to race training (or in humans, aerobic exercise, think ‘bulking not sulking’). It may even have a role in increasing the development of fast twitch fibres, essential for sprinting.
For my experiment we’ve chosen 15 horses, currently competing with winnings in the last year at 1.30m+ (although most of the horses have winnings at 1.40m+ and several are what we call Grade A – winnings over £1,000). Each owner/rider kindly submitted a hair sample of freshly pulled hair – we need those hair follicles for it to work! We then will run the hair through PCR (polymerase chain reaction) where the DNA from the strand is extracted then multiplied millions of times. The PCR product is literally the tiniest volume of liquid but contains millions of strands of the required DNA segment. We send that off to a lab in Europe so they can ‘read’ the DNA and they send back a print out with all the letters (bases- remember A, G, T and C?) on it. We can then ascertain if the mutation is present in any of the horses.
The exciting part is we don’t actually know if showjumpers, or warmbloods have the same three different possible mutations that Thoroughbreds have. Will there be a C:C, C:T and T:T or will they all be C:T? My hypothesis is that they will likely be C:C because they need such great power to get over a 1.30-1.50m obstacle – perhaps at a lower level we’d see a greater variety in genotype (that’s the PhD). I am aware though, that show jumping is likely to be just as much of a polygenic trait as racing, so it’s likely that there are a load of genes that will contribute to the horse’s performance, plus all of the environmental factors such as training, a little bit of luck and a great ride on the day. Whatever we find out will be one step closer to knowing a bit more about equine genomics, as this area is an emerging field.
There’s tons of research you can read up on – the best place is the commercial arm of myostatin testing, Equinome.