However, we use to vaccinate every year for Rabies and then found out from a Vet student that the Rabies vaccine is actually good for three years. So now we vaccinate foals at six months, then every three years there after.
Wendy,
The vet student is almost correct. The Rabies vaccine is good for 3 years IN DOGS AND CATS. There is no evidence that it lasts 3 years in horses and the current recommendation is still to vaccinate horses every year. Don't mess around with this disease. It's not worth it. The vaccine is cheap and works very well.
The vaccine is not labeled for pregnant mares but it has been given to many pregnant mares with no ill effects. To give it or not depends on your comfort level and your vet's preference. I will give it if the mare hasn't had it in the last year. If she got it right before being bred then I wait.