MARYSVILLE -- When the rodeo bull Wolf Deer explodes out of the chute at the Salinas Rodeo this week, his bucking will be as wild as a windy Western sky.

But his furious energy is the product of carefully focused breeding, proof that precision pairing is transforming a dusty old sport with one goal: building a better bucking bull.

His distinctive spins, drops and kicks offer strong evidence of the genetic basis of behavior. Including, perhaps, our own.

"We're breeding them so tough, from generations and generations of great buckers," said Cindy Rosser of Marysville's Flying C Ranch, one of a handful of California rodeo bull ranches and home to Wolf Deer.

So fierce are today's superbulls that the odds are stacked against the cowboys before they even straddle the 1,600-pound beasts. A diminishing number of riders stay on long enough to score.

"We need better bull riders because we've bred our bulls so good," Rosser said.

It wasn't always this way. In the early informal days of rodeos, which began as competitions between neighboring ranches, any ill-tempered or "rank" animal would do.

Since the early 1990s, professional bull riding has surged in popularity -- and bulls, like riders, have their own fan clubs. The top ones appear as children's stuffed animals and bobblehead figures and on hats, T-shirts, trading cards and key chains. The Oakdale bull Troubadour has his own Facebook page; others appear in an Xbox rodeo game.

The wilder the ride, the happier the crowd, and so breeding has grown intensely selective, fueled by the popularity of televised Professional Bull Riders events. The business draws more than 2.5 million people to its 275 annual events, and reaches an additional 500 million globally through television. Prize money has grown over the past 20 years from $650,000 to $9.5 million annually. Owners make additional money through breeding after their animals retire.

"There have always been a handful of rank bulls since the start of rodeo -- animals such as Tornado, Red Rock, Bodacious -- who exceeded the rest of the animals," said former rider Edwin Lay, competition supervisor at Professional Bull Riders.

"But now they're producing more of that higher-end type of animal," he said. "There used to be two or three of that caliber in a pen of 30. Now there are 15 to 20. They are harder to ride, but your chance of drawing one of those animals ... improves (the rider's) chances of winning -- as long as they're rode," Lay said.

According to Slade Long of ProBullStats.com, some of the top riders in the early 1980s stayed aboard most of the time. In 1995, the first year data were kept, 46 percent of all riders made it to the eight-second bell. By 2013, full rides had dropped to 27 percent.

Are genetics enough to propel Wolf Deer to the top? Or will injury and experience dampen his spirit, resulting in a ride as lackluster as his distant cousin Toilet Water, who bucked only briefly on his way to the dinner table?

"It's not all genetics. You also need heart," Rosser said, gazing out on a lush pasture where maybe America's next superbull is testing his spindly legs. "They have to want to work."

The best breeding bulls can command more than $2,000 for a tablespoon-size "straw" of semen, with an average bull producing up to 300 straws per collection, worth $600,000. Rosser calls the most precious semen, stored in vats of liquid nitrogen, "liquid gold."

"People flock to the ones that have proven themselves as sires," said Marlissa Gonzalez of American Bucking Bull, which registers animals' DNA and tracks the lineage of every premier cow and sire and their offsprings' bucking success records.

Almost every bloodline has characteristic patterns of bucking, Rosser said.

Bring It's progeny are cool as cucumbers -- and when they pop out of the chute, they go left, then right, then drop a shoulder. Houdini sires famed "spinners," bulls who pivot on their forelegs as they buck wildly.

Descendants of the agile bull Whitewater can turn on a dime, with change left over. And he's a reliable producer: In 1999, the white bull and his three white sons each landed a spot in the ultracompetitive national rodeo finals -- an unprecedented feat.

In the shuffle of genes that occurs at reproduction, Marysville's Wolf Deer was dealt a royal flush.

His ancestors include the flighty and unpredictable Reindeer and Werewolf, a bovine version of TNT, going airborne in an instant. "The Reindeers blow in the air -- there's a 'wow' factor," Rosser said.

But Wolf Deer is still largely unproven -- he bucked so violently in his sole 2013 event that he hurt himself tossing his rider in a mere 3.2 seconds. So he's in rest and rehab in Rosser's front yard.

Reindeer's progeny, such as Reindeer Dippin', a National Finals Rodeo champion bucking bull, are hot, Rosser said. Crossbreeding them is dangerous, she said, because "they'll flip over backward in the chute and ruin themselves."

Twice a year, the animals get their backs tended by a chiropractor.

Most of these valuable cattle are conceived through artificial insemination, but some breeders clone their most favored animals. World Champion bull Panhandle Slim has been dead for years, but four copies of the cranky bucker qualified for the rodeo's World Finals. Owner Jeff Robinson said the original animal was meaner than the clones, but their bucking patterns are nearly identical.

Now that the bovine genome has been sequenced, breeders wonder: Where, hidden deep in that string of 22,000 genes, is the code for bucking?

In humans, the link between genes and behavior is controversial, fueling the "nature vs. nurture" debate. But the "nature" argument has support in a growing list of genes associated with mental illness such as schizophrenia and bipolar disorders, and in left-handedness, ear-wiggling ability, tongue curling, homosexuality, musical perfect pitch and stuttering.

There is no debate on the ranch or at the rodeo, where animals are born to buck.

Contact Lisa M. Krieger at 650-492-4098.

Online extra
Watch a video of Cindy Rosser talking about breeding rodeo bulls at her Sacramento Valley ranch at www.mercurynews.com/extra.

The rodeo
What: California Salinas Rodeo
When: July 18-21
Where: Salinas Sports Complex
Details: In its 103rd year, the California Salinas Rodeo is the state's largest rodeo. Information is at www.carodeo.com.
Why bulls buck: Rodeo bucking bulls are not your easy-going European cattle -- the Angus, Herefords and Holstein that populate most U.S. pastures. Rodeo bulls trace their roots to Texas longhorn and Brahman cattle that survived by tossing off predators.
Riding a bull: Riders must remain seated for eight seconds. Upper-body control and strong legs are essential. The rider tries to remain forward, or "over his hand," at all times. Leaning back could cause him to be whipped forward when the bull bucks. Judges watch for good body position and other factors, including use of the free arm. Half the bull-riding score is for the contestant's performance and half for the animal's effort. A bull rider is disqualified for touching the animal, himself or his equipment with his free hand.

Tougher rides
1995: Riders completed an eight-second ride 46.38 percent of the time
2013: Riders completed an eight-second ride 26.9 percent of the time
Source: Pro Rodeo Hall of Fame and http://probullstats.com