LOUISVILLE, Ky. (AP) _ Churchill Downs is instituting tougher drug testing just weeks before the Kentucky Derby, requiring pre-race blood tests used to detect stamina-enhancing ``milkshake'' concoctions.

Every horse entered in races during Churchill Downs' spring meet (April 30-July 10) will be tested. Failure to comply will result in the horse being scratched from the race and will count as a violation of the policy, the track said Monday.

A ``milkshake'' is made of baking soda, sugar and electrolytes, and is believed to increase the concentration of carbon dioxide in a horse's bloodstream and lessen lactic acid buildup, warding off fatigue.

Penalties for positive results range up to banning a trainer for a year and barring any horses in the trainer's care at any Churchill Downs facility for six months, for a trainer's third offense.

Dancer's Image, in 1968, is the only horse in the history of the Kentucky Derby ever disqualified after the illegal drug butazolodin (bute) was detected.