It's a lot of bull.

We're talking 2,000 pounds.

Mr. B.

Mean Machine. Get off my back, bucking the tide with a ton of flesh and muscle that's just now beginning to stiffen up on damp mornings.

No wonder. Ol' brown eyes is 15 years old, 75 to 80 in human years, has a girlfriend and two kids and hasn't had a decent vacation in the last decade.

It's time for Joe Kool to retire.

"I think he'll wonder why he's not in the rodeo anymore," says Don Gay, seven times rodeo champion and owner of the celebrated Brahman-crossed Charolais. "But we feel like he's done his job. It's just like a guy retiring from work."

Yesterday Gay was poking around the Capital Centre, getting ready for this weekend's Miller High Life World's Toughest Rodeo. More than 250 cowboys will compete in the event, and President and Mrs. Reagan are expected to attend a by-invitation-only show this afternoon.

Tonight's retirement ceremonies for Joe Kool won't include a testimonial dinner. Or--dare we utter the word--a roast. It'll just be Joe tossing his last cowboy, kicking up a few hoof-fuls of dirt and lumbering off to that lonely bullpen out back of Gay's Mesquite, Tex., farm.

Cowboys say it's the end of an era. Time to pass the reins. Pasture City.

Known as one of the hardest bulls to ride in the history of rodeo, Mr. Over-the-Hill has been ridden only once in eight trips to the National Finals Rodeo. If that weren't enough, he's the only bull with his own fan club.

"He's thrown me off so many times," says livestock manager Jerome Robinson. "I had him five times, two at the National Finals, two at Mesquite and once in Fort Worth."

A qualifying bull ride has to last eight seconds. Only 10 people have done that on Joe Kool in the last 10 years.

"I've ridden him nine times and been thrown eight in a row," says Gay. "And I own the damn bull."

You can tell these guys are cowboys. They wear starched and pressed blue jeans and belt buckles the size of manhole covers, and say "pin" when they mean "pen." Gay wears a black satin baseball jacket with his name stitched in white and a diamond horseshoe pin on his two-quart cowboy hat.

Does he say things like "git along li'l dogie?"

"---- no."

So why did he choose a career of getting thrown off a 2,000-pound snorting, kicking animal that looks like a squashed elephant with scoliosis?

"The money."

Gay says he earns upwards of $150,000 a year in prize money, bonuses and endorsements for Miller High Life and Wrangler, and, as he sees it, that's not bad for a 30-year-old high school graduate.

But Gay says he's been off the circuit for the last few months because "I tore all the inside leg muscles on my right leg."

Does bull riding hurt?

"Damn right."

Do cowboys wear any special protection?

"Nope."

But, ahem, does all that pounding tend to damage any vital parts?

"Well, the way you sit, all the important stuff is in front of you, not behind you."

He has ridden the 10 miles or so from the Capital Centre to Jimmy Cox's stables to check on Joe Kool.

Is he Gay's best friend?

"Just about."

Joe Kool is kept at the stables because he can't be in the same "pin" with other bulls. Joe Kool gets along better with people than he does with other bulls, everyone says.

"He's got quite a personality," his owner says.

He eats 10 pounds of grain a day and all the hay he can stuff down his massive throat. And he sleeps--that's right--"anywhere he wants."

The car rounds the corner, kicking up a shower of dust.

"There he is!" Gay shouts, bounding out of the car. "Hey, Joe."

An animal the size of Rhode Island turns its head. It's light brown, with a toupe'e-like tuft of hair, nostrils you could use as mail slots and an expression of total boredom.

"Isn't he great?" Gay says, hopping over the steel fence, scratching the bull's burlap skin.

Mr. Kool yawns.

"He's gentle but you have to be careful," Gay says, eyeing his pet warily. "He likes to have his back scratched."

Indeed, Joe Kool seems to have all the personality of a giant slug. "There are some bigger than 'im, but not very many," says Gay.

Gay grew up on a farm and was riding bulls before he could ride a bicycle. When he was a teen-ager, he wanted a motorcycle. His parents thought it was too dangerous.

"If I believed in reincarnation, I'd want to come back as Joe Kool," he says. "Hell, he only works about 20 seconds a year, gets all the feed he wants . . ."

Gay dips a plastic pail into a garbage can and pulls out the feed. It looks like Meow Mix. It's actually corn mixed with molasses.

As for retirement, Gay says he'll keep Joe Kool at the farm and make sure nobody makes hamburgers out of him as with some other retired bulls.

It won't be so bad.

"He'll get a few more minutes of back scratching," Gay shrugs. "That's better than a gold watch."