It's No Wonder

Horse-Fly
Horse-Chestnut
Horsetail
Horsehair
Horse Liniment
Horseplay
Horsepower
Horselaugh
Horse Sense
Horseshit
Horseradish
Horsewhip
Horseback
Horse-drawn
Horse-Face
Horse Around
Horse Apple
Horse Trotting Rhymes
Horse's Ass
Horseshoe Crab
Charley Horse
Jolly Horse
Draft Horse
Workhorse
War Horse
Dark Horse
High Horse
Sea Horse
Stalking Horse
Racehorse
Lame Horse
Hobby Horse
Rocking Horse
Trojan Horse
One Horse Open Sleigh
A Horse with No Name
All the King's Horses
All the Pretty Horses
Faster Horses
Hold your horses.
See a man about a horse
A one-horse town.
Cart before the horse
Could eat a horse
Enough to choke a horse
Straight from the horse's mouth.
Don't look a gift horse in the mouth.
You can lead a horse to water, but you can't make it drink. 
I have no horse in this race.
If wishes were horses, beggars would ride.
Get back on the horse (that bucked you).
Only fools and horses.
A horse is a horse, of course of course.
And I looked, and behold, a white horse.
They Shoot Horses, Don't They?
That's a horse of different color.