Wikipedia has more on Equinophobia
Equinophobia (from Latin equus, "horse"), also known as hippophobia (from Greek hippos, "horse") is the fear of horses. Equinophobias may also fear other hoofed animals such as donkeys, mules, and ponies. Negative experiences with horses during one's childhood may give rise to this phobia. Equinophobia may also be triggered by falling from a horse. In many cases, people begin to avoid horses and this gradually develops from fear to a full-blown phobia. The phobia can also be caused by a simple fear of the animal itself. A horse's imposing size and weight and large teeth may scare some people, especially children. Encountering a horse or even thinking about horses can result in symptoms like heart palpations, sudden increase in pulse rate, trembling, breathlessness, nausea, crying, anxiety (even if the horse is calm), terror, and panic.
Many treatment options are available for those suffering from it. Cognitive-behavioral therapy is effectively used in treating people with equinophobia by changing thought processes associated with it. Another treatment option is exposure therapy, which focuses on gradually acclimating patients to horses. The first step in this process may involve thinking about horses, followed by looking at pictures of horses. Once the patient is comfortable with the images, they may proceed to meeting a horse, touching a horse, and finally riding a horse. For extreme cases, it may also be necessary to use medication, even though its effects are only short term.