Brave is a pet trait, introduced with The Sims 3: Pets. It is only available for horses.
Horses are particularly brave and courageous are thus better cope with the chaos of sprinkler systems, fire stations, burglar alarms and other disruptive items.
Attributes
Horse will be less likely to be Startled.
Spooked! and Panicked! moodlets will have shorter durations for the horse.