All Thoroughbreds, regardless of their actual date of birth, are given an official birthday of January 1st to keep the age groups easily defined for race conditions. They must be registered with the Jockey Club within a year of their actual date of birth and must be DNA typed to prove their parentage. To be eligible for registration, both parents must be registered and DNA/blood typed and the foal must be the product of a live cover and not artificial insemination or embryo transfer. There are a few other rules which you can review here.
A Thoroughbred must be named by February of its 2-year-old year or a late fee will be charged. Six names in order of preference are submitted by the owner and the Jockey Club will decide which they can have. Horse names can be changed for a fee unless it has already raced or been bred. Names can be up to 18 characters, including spaces and punctuation. All horse names must be approved by the Jockey Club and there are a lot of rules about what you can't use:
- No initials such as C.O.D., F.O.B., I.O.U., etc.
- No names ending in "filly," "colt," "stud," "mare," "stallion," or any similar horse-related term
- No names consisting entirely of numbers, except numbers above thirty may be used if they are spelled out
- No names ending with a numerical designation such as "2nd" or "3rd," whether or not such a designation is spelled out
- No names of actual persons unless written permission to use their name is on file with The Jockey Club
- No names of race tracks or graded stakes races
- No names clearly having commercial significance, such as trade names
- No names that are suggestive or have a vulgar or obscene meaning; names considered in poor taste; or names that may be offensive to religious, political or ethnic groups
- No names from the restricted list (Hall of Fame members, Eclipse Awards winners, Kentucky Derby winners, etc. To see all names that meet the restriction requirement check here in rule 6(F)(15).
As you can see, there are a lot of requirements to meet when selecting a horse name so it can often be a tough task coming up with six names you like to send in on your request. If you are careful to check the Online Names Book to make sure your choices are not currently in use or reserved, it ultimately it comes down to whether the Jockey Club likes the names you selected and they can be quite picky.
If you have acquired a retired race horse who is missing his or her registration papers, you can find out what their registered name is from the identification tattoo under their upper lip. This tattoo is required for all horses who race in North America and is a permanent link between the horse and his registration info. Finding the name is free, and for a fee you can also find out about their career at the track. More on lip tattoos.