I have a 13 year old TB mare, who I've had since 2004. She's had two foals (2006 and 2009) and I've never seen anything like this before. She was leased from about Sept of 2010 until Feb of 2011 and during that time she was on two different properties with stallions. She was never (to my knowledge) anywhere near the studs, and I've asked the girl who had her and was told that there were never any oops moments. However, today my husband and I were out playing with her, and I noticed her udder was a bit more full than usual. I was able to get a milky substance out very consistently. It wasn't terribly sticky, but not very different than what she's produced before during her other pregnancies. She's always been an easy keeper, so she's got a belly, but I never thought it looked like a baby belly. Of course, now I'm doubting myself! I will be calling the vet on Monday to get her opinion and to go from there, but I was hoping I could get some insight here in the meantime!
Thanks to all, I can answer any questions you have :)