For a wonderful treck through the history of horses and the White House enjoy this link: White House Horses

"American presidents throughout history have appreciated the utility and admired the grandeur of the horse. The visual image of the hero elevated on horseback has been a constant presence in equestrian art and public sculpture throughout the world. George Washington regarded horses as a source of pardonable pride, and his warhorses were of great importance to him as loyal companions and symbols of his leadership. A succession of presidents since his time has enjoyed the beauty and skill of these uncomplaining public servants for work, sport, and leisure.

The White House stables, always a hub of activity, progressed from a simple Georgian brick building in 1800 to a High Victorian mansard-roofed structure commissioned by Ulysses S. Grant in 1871. This last stable, expanded in 1891, was extensive enough to include stalls for 25 horses, a carriage house, tack and harness rooms and a living area for coachmen and stable hands.

Before automobiles, all presidents and their families and staff depended on horses for transportation. The primacy of the horse at the White House ended in 1909 when President Taft converted the stable into a garage for his giant steam cars. Two years later the stable was demolished and horses remained available to the White House primarily for leisure or to provide stately dignity to ceremonies and anniversaries. The horses of the Army's Old Guard Caisson Platoon remain a vital part of presidential funerals.