Bloodstock Agent
A person who advises and/or represents a buyer or seller of Thoroughbreds at a public auction or a private sale. A bloodstock agent usually works on commission, often five percent of the purchase price, and can also prepare a horse for sale.  

Blood-Typing
A way to verify a horse's parentage. Blood-typing is usually completed within the first year of a horse's life and is necessary before registration papers will be issued by The Jockey Club.  

Blow-Out
A short, timed workout, usually a day or two before a race, designed to sharpen a horse's speed. Usually three-eighths or one-half of a mile in distance.  

Board
Short for "tote board," on which odds, betting pools and other information are displayed.

Bobble
A bad step away from the starting gate, usually caused by the track surface breaking away from under a horse's hooves, causing it to duck its head or nearly go to his knees.  

Bolt
Sudden veering from a straight course, usually to the outside rail.

Bomb
A winning horse sent off at extremely high odds.  

Book
1) The group of mares being bred to a stallion in a given year. If a stallion attracts the maximum number of mares allowed by the farm manager, he has a full book. 2) A term used to describe a jockey's riding commitments with his agent An agent handles a jockey's book.  

Bottom
1) Stamina in a horse. 2) Subsurface of a racing strip.

Bottom Line
A Thoroughbred's breeding on the female side. The lower half of an extended pedigree diagram.