In her crossover study Pritchard compared calcium levels in five mature Standardbreds receiving furosemide and five not receiving the drug (controls). | Photo: Courtesy Abb Pritchard

Furosemide (aka Lasix) has long been a controversial race day drug in U.S. racehorses—not only for its potential performance-enhancing effects but also because studies have shown that it can alter horses’ calcium balance, a mineral that’s important for bone strength and muscle contraction.

“We usually use this term (balance) to refer to intake minus excretion,” said Abby Pritchard, a PhD candidate in Michigan State University’s Department of Animal Science, in East Lansing. “Essentially, we want this to be zero so we know that the horse’s requirements are being met without wasting or creating imbalances with other minerals.”

So Pritchard measured how long it takes a horse’s calcium balance to return to baseline after furosemide administration. She shared her results at the 2019 Equine Science Society Symposium, held June 3-6 in Asheville, North