In the UK, the breeding, sale or exchange of pit bull terriers is banned under the Dangerous Dogs Act 1991 and people who already own pit bulls must keep them muzzled and on a lead in public.

BBC: NEWS | Americas | Brutal culture of US dog fighting

The impact of all this finely honed breeding and expensive investment on the actual sport of bull riding is that many on the circuit now believe the bulls are improving faster than the riders can keep up with them.

WSJ: Those Who Root for the Bull

Though bucking bull breeders can trace a few lines back to the 1930s, the targeted breeding of bucking bulls did not take off until the 1990s, when DNA analysis became the industry standard for determining parentage.

WSJ: Those Who Root for the Bull