What? I know that not a whole lot of people do them regularly, but why would 3 vets discourage it? You're paying them to do it because you want to know? Not going to lie, that should really be any of their business. Now if you planned on doing something that would harm your horse, then they should obviously discourage it.
I plan to test my mare for OWLS because her dam was an overo, but she ended up solid. I'm just curious and if I ever planned to breed her (probably will never happen), I should know. But I'm curious. I want to know. Odd comparison, but it's all I could think of.
Random.. Did they give a reason for saying not to do it? It's not like it's some expensive procedure.. it's $30