Back when I was 15yo, me and a buddy of mine would fuck his female black lab after school. We'd take turns stuffing our cocks into her little pussy and cum up inside her. Then I got older an moved away to college. I always had girlfriends because word got out that I was fairly big down there. I actually kept growing until I was 20, and by then, even the girls struggled to fit me inside them. Every time I would fuck a girl.. and they would complain it hurt too much, I'd think back at how much fun it was fucking girl dogs. So, after college, I bought myself a house, and a new dog ( female of course ). But I guess I had grown too much for her too because I could barely get my cock into her wet pussy. Then I met Frank. A older guy that takes care of some horses for a elderly woman. After getting to know him, I let him know I'd be curious about fucking a horse. He was all about it, and told me he fucked one of the mares almost every night. So one night I show up to help with chores and we sneak into this young mares stall. He tells me shes only 5 months old, but loves to get fucked. He goes first. I was impressed to see Frank was well endowed too. He stuffed his huge cock into her pussy with one swift push. All the mare did was readjust her hind legs an spread them wider apart. He pumped her an pumped her an each time went balls deep inside her. After about 15 min of good hard pounding... he pulled out and cum on the floor.. Now it was my turn. I took off my pants an hung them up, an took down my boxers. Frank had a big cock, but I had him beat by at least 3". Even he was impressed an made a comment how lucky that mare was about to be. I stood up on the little box we used to reach an i guided my cock into her wet pussy. I kept pushing until I too was balls deep. The mare could tell the difference in my cock from Franks because she spread her legs even wider apart and made grunting noises with each push in i made. This was great. It had been so long since I was able to get balls deep into a warm wet pussy. I picked up the pace, slamming my balls against her pussy. I could hear the horses breathing change an get louder. By now her pussy is soaking wet... even making wet pussy sounds with each thrust. I was pounding her so hard I had to stop an adjust my box because I was slamming her forward into the stall wall. Suddenly the mares hind legs start to shake an buckle. I keep pounding hard an Franks like "dude.. your making her cum". So I grab what little energy I had left and go full throttle fucking her. The mares legs shake more and her hind legs really start to buckle alot. I stop and to my surprise the mare rocks back and forth on my cock, legs shaking and all. After a quick 30 sec rest I go back at it... pulling my cock almost all the way out an slamming it back into her pussy. Suddenly.. I feel a hot liquid around my cock an running down my balls. She was squirting cum and pee on my balls. I was about a minute from blowing my own load so I grabbed her tail an I went as hard an fast as i could until my nuts exploded inside her. The mares hind legs were so buckled her pussy was only about 3 feet from the floor. I pulled out and her pussy made the loudest pussy fart i'd ever heard. I was exhausted to death... sweat pouring down my face. Both the mare and I looked like hell. It was amazing. I "helped" him with chores for about 3 months until I saved up money and built a small barn of my own.. where I got my own horse. A 6 month old mare that I've been training almost every day.