SCIENTISTS at University College Dublin have discovered what makes a horse a thoroughbred, writes DICK AHLSTROM
They have identified groups of genes that contribute to the unique capabilities that make a race horse.
Dr Emmeline Hill leads the work in equine science within the school of agriculture, food science and veterinary medicine. She and PhD student Jing Jing Gu analysed the thoroughbred genome, looking for genes that deliver a horse such as Shergaror Nijinsky.
“We now know that makes them look the way they look and perform the way they perform,” says Hill. “It is the ingredient that makes a thoroughbred.”
Details of their work were published last Tuesday in the online journal, PLoS1(Public Library of Science). They sought to make the connections between genes and the specific traits found in these horses in a paper entitled: A Genome Scan for Positive Selection in Thoroughbred Horses.
“For centuries breeders have been selecting the strongest and fastest race horses and this intervention has led to a transfer of physiological features in the thoroughbred compared to other horses,” she explains.
Important traits include aerobic capacity but also anaerobic capacity and also muscle mass. “They have an unusually large muscle mass. More than 50 per cent of their body weight is muscle,” Hill says.
The traits themselves are no secret, breeders have cultivated them for centuries. “What we have done is try to unravel the genes that contribute to these features.”
Once thoroughbred breeding was under way, those making selections “unwittingly selected for the genes that contribute to these traits”, Hill explains.
She began her study by establishing a collection of 394 genetic “markers” and used these to compare the genes of one group of horses to those of another.
Their work was based on comparing populations of horses, hence the description as population genetics. They compared the markers in thoroughbreds “looking for patterns of genetic variations that are different from non-thoroughbreds”.
At that point it didn’t matter what the genes were for, she said. “We had no pre-conceived idea of the relevance of their position on the genome.”
Once areas of interest emerged, places on the genomes that had noteworthy differences, they began searching for function. “When we found an area that stood out we identified the gene within that region and then asked the question, ‘What are the functions which are enriched within the region?’” she says.
What certain genes were for became known in 2007 with the publication of the complete equine genome sequence. “The sequencing of the equine genome was central for us to be able to do this,” she says.
“The important thing was to identify the gene function that was more elevated than expected.” These soon became very clear. “We found elevated gene function was involved in insulin signalling, fatty acid metabolism and muscle strength. These were significantly over-represented in those regions selected,” Hill explains.
“The genes that are involved in these have been targeted for selection and have led to the lean, athletic phenotype. This could be important knowledge to understand how exercise may be capable of fighting obesity and diabetes. These genes are likely to be involved in the prevention of obesity and diabetes.”
What is true for horses is probably also true for humans, she points out. Lack of exercise is a risk factor for obesity and both are associated with diabetes and the improper handling of blood sugar levels.
Understanding the process in horses may inform our understanding of these metabolic disorders in humans. “We have proposed the thoroughbred as a large animal, in vivo model for understanding metabolic disease,” she says.
One great advantage is the fact that horses provide a “natural model”, whether the horse is a thoroughbred or from the wild. Horses are “flight” animals which are naturally selected for attributes such as speed and stamina, the very traits desirable in thoroughbreds.