Jess it is not NATURAL for geldings to serve mares. That's a fact. Mares can be damaged in a few ways......they can be hurt in the "teasing" phase (kicked, bitten ect), they can be hurt internally and they can be hurt via transmitted diseases that pass from gelding to mare and mare to mare. A mare's reproduction can be ruined by diseases, even maiden mares can get infections from other mares! There are protocols that STALLION owners use to reduce infection risk ect so as to protect mare and stallion (and in turn other mares in the herd).....thats good stud management and that would be considered "normal" practise. So there is a huge difference between a mare being at stud to be served hoping to produce a foal the following season, and a mare at stud being served by a gelding who thinks he is a stallion. I do not know of a single commercial stud that would allow a gelding to serve mares...either their own or clients.