Does This Make Any Horse Sense?

By Christine Gorman

For nearly two centuries, selective breeding has been used in an effort to produce Thoroughbred racehorses that are faster and have greater staying power than their forebears. At stake is not only the conformation and temperament of the horses but the many millions of dollars spent these days by owners and fans on the sport of racing. Yet according to a report in last week's Nature, the British science journal, today's Thoroughbred racehorses do not run much faster than their great-great-grandsires did. What is more, they probably never will.

The reasons, argue two Irish researchers at the Agricultural Institute and Trinity College in Dublin, stem more from basic physiological constraints on size and swiftness than on the failings of equine genetics. Says Barry Gaffney, a co-author of the report: "It's quite possible from our data that horses may have reached the limits of their speed."

All Thoroughbreds the world over are descended from three stallions imported to England from Arabia and North Africa around the beginning of the 18th century. Since that time, horse breeders have mated only the best with the best, producing such proud champions as Eclipse, Man o' War and Secretariat. For generations, only 6% of all male horses in Britain and the U.S. have been used for breeding. Still, racing times have not improved dramatically since 1910. In the meantime, human Olympic runners have become at least 20% faster than their turn-of-the-century counterparts. Could it be that racehorses are overbred and that there is not enough variation in their gene pool to produce faster animals?

Geneticist Gaffney and Colleague Patrick Cunningham set about trying to answer that question in 1985. For 18 months, they pored over the handicap ratings for 31,263 British racehorses. After evaluating the performance of every three-year-old in Britain from 1966 to 1985, they confirmed that the best horses were not getting any fleeter, but the pack was running faster. Their conclusion: though the gene pool was improving, the top horses had reached their physical limit.

Horsefeathers, say critics. Poultry and livestock bred under similarly selective standards continue to show marked improvements. "If horses aren't getting any faster, it makes one wonder what horse breeders have been up to," comments William G. Hill, professor of animal genetics at the University of Edinburgh in Scotland. Thoroughbreds need new blood, he suggests, and breeders should consider mating them with other kinds of horses.

What seems logical to the scientific community, however, may be anathema to the racing world. Crossbreeds are automatically disqualified from the most prestigious competitions, such as Ascot and the Kentucky Derby. Dramatically different training does not seem to be the answer either. Although human runners have improved through intense physical training, "you can't explain to a horse why it should train harder," says Brough Scott, a British horseman and author. An overtrained Thoroughbred simply goes sour. "Horses tend to be like a machine," explains James Rooney, head of veterinary science at the University of Kentucky. "About 40 m.p.h. seems to be their top velocity." All of which may make picking the winner a closer call than ever.

With reporting by Shelagh Donoghue/Chicago and Paul Hofheinz/London