Oak leaves and acorns, in large quantities, are poisonous to horses.

Oats are a popular feed for horses. They are bulky and help prevent impactions. They can be fed whole, rolled, or crimped.

Oat hay is a good feed for horses. It is low in protein, and can be fed together with a legume (such as alfalfa). Early cuttings are more nutritious and contain more energy.

A system that rates lameness in 4 different degrees. It was developed by Niles Obel in the 1940's. Obel Grade 1 is when a horse shows frequent shifing of weight between the feet, but no visible lameness at the walk, and bilateral lameness when trotting. Obel Grade 2 is when a horse does not resist having a foreleg lifted, nor does it resist to walk, but it does show lameness at the walk. Obel Grade 3 horses object to the foreleg being lifted, and are reluctant to walk. An Obel Grade 4 horse will only walk if it is forced to.

The bone at the rear of a horse's skull, to which the vertabrae are attached.

On a Western saddle, the Off Billet is a strap (usually leather) that holds the cinch up on the horse's off side. It has holes punched in it so the cinch may be adjusted. On the near side, the cinch is tightened into place via a latigo. The off billet is shorter and usually made of stiffer leather than the latigo.

Horse racing term. The official that assigns weight to a racehorse to be carried in a handicap race, based on the horse's ability.

While the left side of a horse is called the near side, the right side is the 'off side'. See NEAR SIDE.

Refers to an ex-racehorse of any breed that raced on the track. For example, "Do you like my new horse? She's off the track", or "He's an off-the-track gelding".

Horse racing term. The official that assigns weight to a racehorse to be carried in a handicap race, based on the horse's ability.

The next rider up in an event. The person who is "up" is to enter the arena or start their event, the person "on deck" will be next to enter, and the person "in the hold" is 3rd up.

When a horse carries his head tucked in, nearly vertical, and his mouth is below the rider's hands. In this position the horse is responsive to the rider, and is said to be 'on the bit'.

Refers to a show or event/class in which all riders and horses, regardless of age, ability, or money won, can enter. For example, an event may have a 'youth' class (for riders under a certain age), a 'novice' class (for riders or horses having won under a certain amount of money), and an open class (open to everyone).

Racing term for a bridle that does not have blinkers or blinds on.

Refers to a barrel horse that is good enough to compete in "open" classes or rodeos and place. Calling a horse "Open" usually implies that the horse does not need to run in 4D classified races, because the horse is good enough to place in events which riders compete and the fastest few win (instead of a 4D where places are paid in different time divisions).

A mare that is not pregnant. Note: Depending on context, may also mean an open barrel horse that is a mare (see Open Horse).

A foal whos mother has died before the foal has been weaned (or while the foal is still dependant on milk).

An old cowboy term for a horse that was unable to be ridden.

Refers to a horse's dam. A horse is "out of" his dam, and "by" his sire.

During a cutting competition, if the horse fails to respond quick enough to keep the cow under control, it is said to be out of position and loses its working advantage over the cow.

Horse racing term for a horse that has little chance of winning.

A piece of tack that hangs from the saddle horn and is swung over the saddle to encourage the horse to speed up. Usually made of a piece of rope with a fuzzy end or a piece of braided cloth or leather.

A type of pinto coloring. The term "Overo" basically means a pinto that is not a tobiano (instead is one of the 4 other pinto colors). Overo horses can be sabino, splashed white, or frame colored, or can carry a mix of these genes. Many people use 'overo' also as a term for just Frame Overo, which is a specific pinto pattern.

When a horse strikes his front leg with his rear hoof, he has 'over reached'. Most horses that over reach step on the back of the heel of their front leg, which can cause painful bruising or even take off part of the heel.

A small boot that fits around the horse's coronet band and protects the horse's front legs in case the horse over reaches. They are made of either rubber, which will deflect a hoof, or made of cloth or padded material which will prevent wounds or bruising in the case of an over reach. Often worn in horses that are required to run and stop quickly, such as barrel horses and roping horses.

See "Parrot Mouth".

Two jumps that are placed 6 inches to 5 feet apart that a horse must jump in one leap.

An oxer jump in which both jumps are the same height.