>>90121960FEMALE HORSES
F = Female horses less than 5 years old are called “Fillies.”
M = Females 5 years and older are called “Mares.
MALE HORSES
C = Colt, (male horse aged under five years, which hasn't been gelded)
G = Gelding (castrated horse)
R = Ridgling (male equine with a retained testicle or one which has been incompletely castrated)