Breeding older horses produces slower foals

Prize racehorse owners may need to stop breeding their animals deep into old age as a study shows that offspring will get slower the older the sire gets.

Analysis of more than 100,000 horses found that after the age of six a male’s offspring gets slower by 0.011 yards a second for every year the sire ages. A similar trend was seen in dams whose best years for breeding speedy foals are between four and six.

“For context, [this] translates into a predicted difference of approximately one second over a race of 1,760 yards (one mile) between a five-year-old and a 15-year-old mother,” the researchers write in their study, published in the journal