Glenda,
A health certificate is normally only good for 30 days and the time it
is good for varies between states. Some states, including Florida,
require a Coggins test within 6 months of entering the state. The
Coggins test is a blood test for Equine Infectious Anemia (antibodies)
and is different than a health certificate. The vet will take the blood
for the Coggins test and mail you the results. I think that proof of a
negative Coggins test is required for a horse's health certificate. I
also believe that Florida is one state that will stop you at the border
for your health certificate and Coggins paper and detain you until they
get a vet out to inspect if you don't have them! Happy traveling!