But when you are told a horse is a gelding, how many actually check and feel for anything? This gelding, if I read right, does not belong to the OP and so I highly doubt that they went to check the gelding to see if anything was there under the skin. Another forum member had a mare luted after getting bred by the BO's "gelding". It turned out that the "gelding" wasn't a gelding at all and the barn owner had actually bought a stud colt who hadn't dropped yet, then pastured with mares at the time he actually did drop. It is possible that the gelding in this case, is a gelding and just shooting blanks. The mare could have had a spike in hormones from the "breeding" and goes into a false pregnancy that could last a couple months or a full year with the complete works of bagging up and a false labor before it ends. The biggest concern for me with a gelding mounting and "breeding" is the risk of uterine infections and injury to either during the process.