Overview.
A horse that is produced, bred, and trained for use in horse racing.
The thoroughbred is particularly famous as a breed.
A racehorse's pedigree is considered an important factor in determining the horse's ability. In the world of racehorses, even if a mother is a famous horse, she cannot even run if her father's pedigree is unknown (e.g., mother, Morikei, son, Hiyoshimaru. At the time, Morikei was talked about as an "unmarried mother. Hiyoshimaru became a horse rider because his pedigree was unknown). If a pedigree is lost for some reason, or if a horse has an unknown pedigree, it is not considered a Thoroughbred unless it can be proven (→ Sala-kei), and the horse will be branded as such for the rest of its life, no matter how many wins it has achieved, even if it is a champion, and breeding is affected. In the case of stallions in particular, even if a mare becomes a stallion, all of her offspring will be treated as "sara-kei", so breeding opportunities themselves are extremely rare (e.g., Hikaru Imai, Hikari Deyur). In addition, a thoroughbred mare is now recognized as a thoroughbred if she has been bred to a thoroughbred for eight consecutive generations and has been approved by the International Pedigree Committee. (Narita Meister)
As a result, as of FY2021, only one thoroughbred mare has been registered.
In recent years, in order to preserve the bloodlines of Anglo-Arab mares associated with the ranch, some Sarah-type horses (formerly known as quasi-Sarahs) have emerged, in which Anglo-Arab mares with little Arab blood are bred to thoroughbred stallions. (Gordie)
In the Japanese horse racing industry, there are many cases of euthanasia (simply put, killing), mainly when some racehorses are judged by veterinarians to have a poor prognosis due to injuries or breakdowns caused by accidents or problems in or outside of races, or due to worsening medical conditions.
The reality is that only a minority of horses live out their natural lives after retiring from racehorse racing, and many issues remain regarding their second careers (5% of Stallions Can Become Stallions- NumberWeb).
