Kasey Hayes hopped on the bovine beast trapped in the narrow holding pen like he'd done hundreds of times. He adjusted a tight rope on his left hand, found his balance and signaled he was ready to dominate the bull for the next eight seconds - or, at least, hoped to.

The red metal gate swung open. The bull's spine rolled, the animal charged forward and stood on its rear legs. The crowd cheered as the first ride on this March evening appeared promising. After 3.72 seconds, Hayes lost control, hit the ground and got his head stomped on by the 1,600-pounder named Shaft. His hockey-like helmet split in two. The arena fell silent.

"Come on Kasey. Come on son. Wake up," a woman in the stands said as Hayes lay surrounded by doctors and athletic trainers. It took about a minute or so before Hayes could be helped to his feet. He had a concussion - the third in a 12-month period.

Serious injuries are occupational hazards for bull riders, but doctors, riders and researchers say the most pervasive injuries are concussions. The Professional Bull Riders' circuit provides a stable of doctors, requires helmets for anyone born after 1994 and insists concussed riders pass a test before getting back in the saddle.

But in this era of concern about head injuries in the NFL and NHL, the circuit's lead medical staffer says he hasn't seen a drop in the number of concussions despite the widespread use of helmets. There are no multimillion-dollar contracts or unions in professional bull riding; if you don't ride, you don't eat, leading to athletes to push themselves back into action.

Few researchers have looked into the number of rodeo injuries, and very little data is available to detail the rate of concussions. The largest available set, collected from 1981 through 2005 at nearly 2,000 Professional Rodeo Cowboy Association-sanctioned events, shows 859 concussions were registered during various competitions such as calf roping, bareback riding and bull riding.

That amounted to 52.1 percent of all major injuries, and "anecdotally, the vast majority of them were bull riders," according to Don Andrews, a retired athletic trainer who established the first sports medicine program in rodeo and assembled the data.

Concussions are the result of the brain banging against the skull. Side effects range from loss of balance, constant headaches, confusion, dizziness and vomiting. Recovery can take weeks or months, depending on the severity.

More than a decade ago, a group of health care experts - including the PBR's longtime medical team leader, Dr. Tandy Freeman - developed a set of guidelines to prevent and manage concussions and encourage the use of protective head gear.

Currently, all circuit riders must wear a protective vest, but only those born on or after Oct. 15, 1994, are obligated to use a helmet. Freeman said that the PBR, much like the NHL in the 1970s, decided to grandfather in helmet usage, though most riders wear them now. But helmets don't prevent concussions, Freeman said.

"What I can tell you is that there does not appear to be a statistically significant difference between riders with helmets versus without helmets in the number of concussions received yet," Freeman said.

Freeman and the athletic trainers who travel to the nearly two-dozen events a year gather baseline cognitive data at the beginning of the season, noting each rider's memory, balance and reaction time. If a rider sustains a concussion, the medical team administers the tests again. Freeman can sideline the rider if he fails.

"About 16 percent of the injuries we deal with are concussions then from there everything is broken up pretty much into thirds," Freeman said.

The only visible sign of Hayes' close encounter was a scratch extending from behind his left ear to his jaw.

"It was my turn I guess," the 29-year-old Liberal, Kansas, native said. "When we get on bulls, things usually don't go bad; you usually do what you're supposed to do ... But when things go wrong for us, it's a little worse I think than in other sports."

Hayes was ordered to take at least a week off from competition, an order he said he'd follow; he hopped on three bulls the following weekend. Hayes currently is sidelined after breaking three lumbar vertebrae in late April.

Some riders lie about their symptoms to try to fool doctors into letting them ride again.

"If you don't compete, you don't get paid at all," said 26-year-old Stetson Lawrence, of Trenton, North Dakota, who last suffered a concussion a couple years ago. "Most guys, just to do a test on their bodies, ride a horse to get the movement and see if you can handle it and see if you are dizzy after, you get off."

The most serious consequence of repeated blows to the brain is chronic traumatic encephalopathy (CTE), a neurodegenerative disease. Symptoms include memory loss, anxiety and progressive dementia, and can only be diagnosed after death.

"We don't know if people who have had one concussion are at a higher risk to develop this or if it takes three concussions or if it takes a lot more than that ... some of the evidence that's out there showing that if you do sustain multiple concussions you are at a potentially higher risk to have CTE or issues later on in life," according to Dr. Richard Figler, co-director of the Cleveland Clinic's Concussion Center.

CTE has been diagnosed in former NFL players (including Hall of Famer Junior Seau), NHL players (most recently, late defenseman Steve Montador) and boxers, but no research has shown whether former bull riders have been affected.

If Thad Bothwell started his career all over again, he'd likely wear a helmet instead of a cowboy hat. Bothwell, who retired in 2002, broke several body parts and logged about a half-dozen concussions.

"My son competes now and he wears a helmet," said the 46-year-old from Rapid City, South Dakota. "I recommend helmets. Now they are really trying to keep riders from really messing themselves up.

"Back in my days, if you knocked your face, you got on. Back then, we didn't have someone making that decision for us."