Racehorses have 'radiator' to stop them overheating

Scientists have solved the mystery of how a racehorse is able to gallop at full speed without passing out from an overheated brain.

Scientists have solved the mystery of how a racehorse is able to gallop at full speed without passing out from an overheated brain.

A miniature "radiator" in the horse's head dissipates heat from the blood supply to the animal's brain, the most heat-sensitive organ in the body, according to a study published in the journal Nature.

Scientists had been puzzled why galloping racehorses do not collapse, since the blood temperature of horses when exercising can reach more than 40C, high enough to cause heat stroke and even brain death.

Keith Baptiste, a veterinary scientist at the University of Saskatchewan in Saskatoon, Canada, found that the blood supply to a horse's brain is cooled as it flows over a pair of air-filled chambers called guttural pouches. "The main blood supply to the horse's brain is via the internal carotid arteries which pass over the back of each pouch for 13cm of its length before entering the brain," Dr Baptiste said.

"As the hot blood passes over the guttural pouches, en route to the brain, it gives off heat to the cooler guttural pouches. The pouch membrane is paper-thin to help facilitate this heat transfer," he said.

The air within the guttural pouches remains cool, possibly as a result of the evaporation of moisture taking away heat much like the ability of sweat to cool the skin. "It is the difference in the two temperatures - internal carotid blood and guttural pouch air - that drives this heat transfer," Dr Baptiste said.

The findings could have implications for humans as well as racehorses. "Recently, it has been found that people who experience stroke and head trauma also experience high brain temperatures. So now there is much interest in human medicine in trying to explore if brain-cooling would help people," Dr Baptiste said.

Experiments on goats show that, as their brains heat up, their athletic performance goes down, possibly as a result of the brain protecting itself from heat damage, he said.

"We are not interested in galloping goats, but we are interested in galloping horses, so brain-cooling may well have something to do with racehorse performance," Dr Baptiste said. "This is what future research needs to find out."

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