Inbreeding in the thoroughbred population is “akin to global warming” according to a new research paper published by University College Dublin.
Professor Emmeline Hill (pictured) analysed the DNA of more than 10,000 thoroughbreds, the largest set of horses examined to date, and established that there has been a highly significant rise in inbreeding over the last 45 years.
The research linked the increase in inbreeding to selection for favourable racing traits and the influence of popular sire lines, with 97% of horses in the study tracing to Northern Dancer, 35% of European horses having Sadler’s Wells in their pedigree, and 55% of Australian horses having Danehill in their pedigree.
“Inbreeding has always been high in thoroughbreds, but it is getting higher,” Hill said in a statement. “It’s likely that, unchecked, inbreeding in the thoroughbred will continue to increase in a market where there is high demand for particular sire lines.
“The problem with inbreeding is that it can compromise overall population fertility and health. This is a highly significant issue akin to global warming, where inbreeding is accumulating in the population, and it must be addressed at an industry-wide level.
“Our new data can assist the industry to monitor inbreeding and we have developed DNA-based tools that individual breeders can use to reduce the problem by choosing genetically diverse stallions for their mares,” she said.
“Pedigree is not powerful enough to help any more. Pedigree can be useful in highlighting broad trends in breeding practices, such as the predominance of certain sire lines leading to a high degree of relatedness. However, since Thoroughbreds are now so closely related, there is no longer the resolution in a pedigree to accurately infer relatedness between individuals.
“Multiple studies show that pedigree-based estimates of relatedness are less accurate than DNA-based methods, which measure the true genetic relationship between individuals. Suitable outcrosses will be best identified using genetic data.”