I have a 7 y.o. TB gelding. I have had him 11 months, and he was gelding about 1 year ago. We have a mare, and we have another gelding. My TB is crazy about the mare, and usually he goes out just with the other gelding. Occasionally, the three will go out when the pastures are lush or there is a round bale. The other gelding is at training this month, and I started putting my TB and the mare out together, but he comes in overnight. They seemed calm and happy at the end of the first day. About the second day, he was quite happy to go out, and he was ‘hanging’, which seems to be his norm when around her, at least initially. The mare was also sniffing him. Excuse my french, but it seemed like he had an erection this last time. When they are separate (minus the other gelding), they seem to call to each other at first, then settle down. Is this normal behavior, or should my TB gelding have settled down by now? I was hoping he would have settled down by now. . . .could this also be why he also turned into a reluctant trailer loader since coming to his new home?
Castration is not a lobotomy. I have known geldings to mount mares in season…which is why there are sex-segregated herds.
If both horses are yours, and the mare lets him, then let them be horses. She will tell him when she’s had “enough.”
There is no correlation with the trailer loading…other than he decided not to load.
Also keep an eye on the mare. Mares go into heat roughly every month through the spring and summer. If she is around a gelding that has studly tendencies that might make her more exuberant in her behavior. You might want to separate them during these times at least if they get too amorous.
The amount of residual studly behavior in geldings varies a lot.
Even boy horses who are gelded young sometimes are able to mount and penetrate mares. Yours was gelded at 6? He will likely retain some stallion mannerisms his whole life. Not a surprise.
Brought a friend’s mares here during an evacuation for wildfire. The gelding was totally captivated and dropped. I kept reminding him that one of them was his sister. He didn’t care.
A personal aside. Yes, geldings can mount and penetrate if the mare lets him. Having said that, a gelding may not be the cleanest and you may be risking getting an infection in your mare.
Many, many years ago and before I knew better, bred my mare to a stallion who wasn’t properly cleaned up before breeding and she ended up with an infection we had a hard time clearing up.
Best to just sex segregate the boys and the girls 
I had a Hackney pony who was gelded quite late (age 12), and definitely not a cryptorchid. When I got him, he was 22, so ten years after he was gelded, and he exhibited stallion behaviors until he died. He occasionally mounted my Paint mare who was three full hands taller than he was. I used to get irate calls from my neighbors: “Do you know what your horses are doing in the pasture?”
He always seemed to view all geldings and stallions as competition, and mares as prospective girlfriends. He tried to mount my friend’s mare while I was driving him and she was riding the mare. Dammit, I told my friend to back her mare off, but she didn’t listen, even when the squealing started. The friend never let her mares come that close again, at least.
Rebecca
My gelding would mount mares in heat and had the capability to complete the act.
At first we thought he was just mounting but once we realized it was more than that we kept them separated when the mare was in heat(it was my friends mare and we kept them together in my little backyard barn/pasture).
He only ever did that in a pasture setting, but would flirt with girls any time!
