Confound it! Big Mac thought entering the barn, closing the door behind him. Can’t get this boner down a notch.
It was sweltering hot this afternoon. For some reason, he couldn't get his erection to unharden since this morning. Even after showering, it did nothing to soften his morning wood. He also wanted to pee so badly, trying desperately not to wet outside. Mac closed the doors behind him hoping nopony would find out. He slowly walked around the barn, his knees shaking nervously as he was holding his crotch area to prevent leaking out.
Big Mac shyly bit his lip and looked around the area for a good spot to pee on. His eyes focused on the empty spot near the water hose. Standing near the wall, he sighed as he unzipped his pants.
Closing his eyes, he let out a long moan as he let out streams of urine onto the ground. The sounds of pee hitting the ground brought music to his ears. As he finished up, he heard a sudden bark close to him.
Arf!
He let out a gasp of realization, his eyes widened in horror as he hears Winona bark loudly again. She was covered in his pee! His nose wrinkled as the strong sour smell entered his nostrils. This only made his horsecock even harder. He had an idea as his cock twitched. A sheepish smile formed on his face.
“Mind if I help clean you up?” He asked Winona.
She nodded and let out a playful bark.
“Good.” His smile widened.
He walked Winona to the other side where he took his pants and shirt off.
He sat down with Winona and pet her in the head. Sweat formed around his forehead as his mind was clouded with filthy thoughts of having sex with his own pet dog, his hardened cock twitching in pleasure.
That’s a good doggy! He groaned in delight seeing Winona move up and down his wet black thick stallionhood. Oh yes!
His mouth watered at the thought of committing bestiality, his eyes looking upwards. His daydream was cut short when he saw Winona lift her rear leg and let out streams of her pee onto his leg.
Big Mac bit his lip as Winona continued to urinate on his lower leg. He grabbed his harden cock and started slowly stroking his erection, letting out small moans of pleasure as he lowered his horsecock close to the peeing dog. Droplets of urine landed on his thick stallionhood and hand causing him to rub his erection faster as the musky smell and Winona’s louder, rapid panting increased.
Pre-cum leaked from his throbbing erection. He continued masturbating with Winona’s pee, lewd loud wet squishing sounds filling his ears. He closed his eyes hard and let out a loud grunt as he suddenly ejaculated blobs of gooey semen onto Winona’s already urine covered body, lightly humping with his hand as he continued to cum to his pet. Semen landed on Winona’s back, some splattering onto her paws, legs, tail and face.
Winona let out a happy loud bark.
“Good girl,” Mac said lustfully, taking a slow teasing sniff at her pee semen covered body making his erection twitch harder "Damn that’s hot!"
However his erection still didn’t go down. He then had another idea as a smirk formed on his face. His erection tapped on the dog’s buttocks, her tail teasingly stroking Mac’s black thick horsecock.
“Does doggy want a treat?”
She nodded, barking happily and panting loudly.
He let out a moan of delight as Winona took a sniff at his cock, small amounts of precum landing on her muzzle. Mac gritted his teeth as Winona nuzzled his cock making the stallion drool in pleasure. Winona then dragged her wet tongue up Mac’s throbbing cock causing it to twitch.
Mac whistled lustfully as his cock was covered in thick, slobbery, musky saliva. Winona continued to lick around the stallion’s horsecock, slobbering all over the tip and side of his erection.
“Now. time for get you cleaned up” He said in a low, horny tone.
Petting Winona as his cock was twitching for attention, he rubbed his dog smelling cock on top of Winona's ass, groaning in intense pleasure as his thoughts on screwing his dog pet who is covered in sticky smelly musky semen and urine took over. He sniffed at the dog’s rear and used his two fingers to rub around her vagina.
He slowly pushed into Winona’s vagina, his thick cock slowly penetrating inside of her folds. Big Mac thrusts into her, moaning even louder as he continued to fuck her. Loud wet squelching noise echoed the barn, Mac panting loudly like a dirty dog. He felt like he was in doggy heaven. Winona lifted her rear leg making Mac pick up speed, thrusting even faster into her semen covered butt. The vaginal walls kept Mac’s cock nice and snug invoking him to whimper in delight at the intense sexual pleasure.
“Ain’t you a tight one?” Mac let out loud grunting noises, his horsecock throbbing as he is close to climaxing. He moved his tongue into Winona’s dog-smelling mouth, moaning lustfully as he continued humping like no tomorrow. Both of their tongues getting wetter and sloppier by each second. Saliva strings connected as they broke up their make out session. He grabbed Winona’s butt with his hands and began pumping into her arousal hard.
He couldn’t believe it! This is one of the most sickening, deprived, and weirdest ways he’s ever done. And he wanted more! Not only Winona was dirty, but so was he! Much louder squelching sounds echoed his ears as he was close to cumming inside of her.
When things couldn’t get even more disgustingly hot, Winona started leaking out more of her urine onto Mac’s cock. The musky wet dog smell seeped into his nose causing him to let out a moan. He couldn’t take it anymore. He let out a very loud wolf-like scream as he finally came, unloading gallons upon gallons of his seed into her cunny. He panted hoarsely as he continued to thrust wildly into her.
Mac sweated profusely at the sight of fucking a dirty doggy, more gooey cum splattering inside of her pussy lips.
“Feels so goddamned good!” He said to himself loudly.
Mac slowed down, giving a few more weaker thrusts before pulling out from Winona’s ass with cum still landing on her buttcheeks.
With his cock softening, he sat back down as Winona jumped onto him and licked around his face. She turned around and lowered her face to his cock, licking off some of his semen. He sighed in relief at the sight of Winona’s wet musky cum dripping pee covered arousal. Winona once again lifted her rear leg and began licking herself.
However his eyes widened in horror as he heard his sister entered the barn, looking surprised at the sight of Winona looking oh so very dirty. Mac laughed nervously at Applejack as she frowned upon him.
“What in sweet tarnation is all of this?” She asked as the smell of the hot musky sex filled her nostrils causing her nose to wrinkle in disgust. “Did you and Winona play in the pig farm again?”
“Eeyup.” He answered bluntly.
Applejack facepalmed in embrassement. “Looks like doggy here needs to be cleaned again!”
“Eeyup.”
“And try not to walk Winona to the pig farm this time,” she said “She stank like a bad tomato a week ago and we know how that ended up.” She rolled her eyes.
Eeyup. He thought to himself, his softening horsecock suddenly came hard again.
Applejack looked at his erection in awe causing Mac to blush in shame.
Whoa nelly! She thought to herself, blushing in embarrassment. In second thought, I got two doggies to be clean up and I reckon it’ll be worse than last week.
Author's Note
I have no idea on why I've written this thing or clopped to Winona/Big Macintosh. Oh well. I had to write this some day. 
