I had a yearling filly last year that had perpetual snots. Always white, never green. Had the vet with her several times. He finally came to the conclusion that it was allergies. Quit showing on the filly, turned her out, let her grow and toughen up, and she is at the Nationals now with a dry nose, and it has been dry all year! However, if your horse has green coming out, you better get the vet quickly. You don't need to give minis a lot of antibiotics anyway. It can kill the good bacteria and you could have a grade a colitis problem. Our rule here is no antibiotics unless the vet says so, and then pray. We have lost one of our minis before because of too many antibiotics, prescribed by a veterinarian that wasn't familiar with mini medications!