Yes, you read the title correctly. To start off, I have already spoke with my vet and we will be trying a few different things and pulling blood in a few weeks. My vet has never heard of this problem, so I thought I'd post here to see if I can get any other ideas. I will attempt to keep this as short as possible.... I have a 27yr old NSH whom I have owned for 12 years now. He has always been pastured with mares, geldings, foals, and has been around stallions as well. I noticed a slight bit of the behavior this fall, but very briefly. Enough to puzzle me, but I never saw it again so quickly forgot it. My gelding lives in a pasture with a 20yr TB gelding, 9 month intact colt, and 7 month filly. This field shares a fence line with my 13yr old Stallion, coming 3yr intact colt, and 6yr gelding. For the past week the hotline has been loose or down between the pastures. I put it back up but have not been able to figure out who is doing it, until today.... I find my 27yr old gelding teasing my 3yr colt. Yes, teasing. He is backed up to the fence, bent at the hocks squatting (just like a mare breaking down in heat), tail lifted and off to the side, and peeing. Peeing everywhere! Not a normal stream, bursts of urine like a mare in heat. I go into the pasture and chase the gelding away (colt is leaning on the fence, hanging out, and clearly wanting to mount the gelding), for him to only come running back to the fence every time. Backing up to the line and nuzzling/nipping my colt. This gelding has always loved his mares and been very protective of them and their foals, unless I have a more dominant gelding in the field. I have noticed little signs from him the past year that make me wonder if he may have a bit of dementia. He has a thyroid goiter and is on Iodine for it (Thyro-L makes him colic off and on, no clue why). Otherwise no health issues. I found him down this wed and he wouldn't eat. I checked him over and he had an incisor that was split and infected, it was extracted the next day (thursday). He was given a shot of antibiotics and I have SMZs to give him for 10 days. My vet wants to up the dose of Iodine for 3 weeks to see if we can kick start his thyroid (thinking its throwing off hormones). Last time levels were checked, they were normal. If the behavior does not change, we will pull blood to check progesterone/testosterone levels. We will check for cushings as well. Aside from this, we are thinking some kind of tumor. The gelding has been removed from the pasture and put back with his mares for the time being. Does anyone have any thoughts on this?