By The British Warmblood is a gathering of types of British-bred sports horses rather than an actual breed. There are strict selection criteria to be met, but the bloodlines of the various horses which classify as British Warmbloods cover a multitude of breeds. It’s all about racing, you see: The aim is for the horses to have the potential to be a successful international sports horse.
ORIGIN: The United Kingdom
ENVIRONMENT: Open habitat including grassland, moor and heath
USES: Riding and sports
HEIGHT: 15.2 to 17.0 hh ( 62 to 68 in)
COLORS: Black, brown, chestnut, dun, gray, bay, palomino and colored
ORIGINS
Britain has long relied on the success of the Thoroughbred and various crosses with it as a source for its race horses, but as demand for such horses grew, many British riders started to look to Europe and the well-established warmblood breeds for top class prospects. In 1977, the British Warmblood Society was formed with the aim of producing a British equivalent that would allow British riders to buy a British rather than European sports horse. Horses have to pass a grading process to be accepted as breeding stock, and an annual show is held where the progeny of graded parents are promoted.
CHARACTERISTICS
The aim of the Breed Society is to produce sound and athletic horses with excellent movement and trainable temperaments. Such horses are suitable for all disciplines. The graded stallions must meet all grading criteria and have at least 50% warmblood in their pedigree. To achieve Group-One status, the stallion must be graded and entered in the British Warmblood studbook, perform tests, be the sire of an advanced dressage or event horse, or be a grade A showjumper.
Source:
Debby Sly: Encyclopedia of Horses. Bath, UK 2008, p. 197
Denney Home Place 
Allow me, as an ignorant horse fan, to ask you a dumb question. What is a warmblooded horse? I thought all mammals are warmblooded.
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It’s got to do with where the horse breed originates from: Hotblooded horses come from hot climates, like the Arabian from the Arabian deserts. They have a fiery temperament and are very energetic. Coldblooded horses come from colder climates, like the forests in the north. Their temperament is more placid. And warmbloods are a mixture of both.
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Thank you for taking the time to explain! It is very much appreciated.
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