There are two types of horses used in horse racing, thoroughbred horses and standardbred horses. Thoroughbred horses compete in flat racing and National Hunt racing and standardbred horses compete in harness racing.

Thoroughbred Horses

In the eighteenth century the jockey club wanted to know the family history (pedigree) of every racehorse in England. The job was given to a man called James Weatherby. In 1791 he published his findings in the "Introduction to the General Stud Book". Since then the W eatherby family have recorded the pedigree of every foal born to those horses in the original General Stud Book in all subsequent editions. From the early nineteenth century only these horses were allowed to race. In his findings he found that every single horse could be traced back to one of three stallions, called the "foundation sires". The three stallions are the Darley Arabian born 1724, the Godolphin Barb born 1724 and the Byerley Turk born 1680. The offspring of these stallions produced horses with excellent speed and stamina which is why they were originally used. An American version of the Stud Book begun in 1873.

Some races are only for horses of one sex, whereas others can be entered by either sex. Young female horses are known as fillies and older females as mares. A castrated male horse is called a gelding.

The birth of all thoroughbreds is said to be the 1 st of January of the year they are born, irrespective of the actual date. These horses begin training after about a year and by the age of two they begin racing. At around 5 years old they usually reach their peak. Although in the past horses older than 10 have won some of the biggest races around, especially steeplechases.