Well, it's more expensive, for one thing.

The mare has to be put under general anesthesia, and it IS more invasive by a large margin than gelding.

But it does make for a much steadier animal.

I've heard some propaganda that it causes cancer in the mare... but I've found nothing concrete supporting this.

We need more people speaking out. This country is not overrun with rebels and free thinkers. It's overrun with sheep and conformists. - Bill Maher

The very existence of flame-throwers proves that some time, somewhere, someone said to themselves, You know, I want to set those people over there on fire, but I'm just not close enough to get the job done. -- George Carlin