Your domestic shorthair cat is cute, sure, but is he cat-contest cute? That all depends on which cat contest you're talking about. Domestic shorthairs, unlike specific breeds, don't have the pedigrees or paperwork that are required to enter many cat fanciers' competitions. Still, your domestic shorthair can compete in less formal arenas.
A Question of Breeding
Your domestic shorthair cat might look a lot like a purebred, but genetically speaking, he's a hodgepodge. Most cats are the culmination of thousands of years of unadulterated breeding.
The domestic shorthair has a distinct combination of expressed and dormant attributes -- with far more variables than in a purebred cat. That's because his bloodline is muddied, less distinct than those of his aristocratic brethren. He's the mutt of the cat of world.
Pedigree and Papers
Purebred cats often have pedigrees -- family trees showing ancestor lines -- and formal papers. The idea is that genetically, such and such line is known for such and such traits.
Your domestic shorthair might display some of those traits, but there's no guarantee that his offspring would. That's why few people keep pedigrees for domestic shorthairs.
That shouldn't stop you from praising and celebrating your cat's distinct attributes -- even those that aren't associated with more distinguished lines. It's just a question of whether anyone else will recognize his greatness.
It's All About Association
If you want your domestic shorthair cat to compete in a cat competition, find out which association's criteria are in play. You can call the event organizer and ask whether your cat is acceptable. The Cat Fanciers' Association, a large cat-governing body, doesn't recognize domestic shorthair cats among its 40 pedigree breeds and two miscellaneous breeds.
However, some other organizations set aside a general-entry category open to domestic shorthairs. If you're looking into a 4-H competition, your domestic shorthair should be allowed. Note that some organizations distinguish between American and domestic shorthair cats. You might have to ask a vet which one your cat is.
When showing your domestic shorthair cat, remember that any field that accepts him is wide. Play to his strengths and distinctions to separate him from the herd.
Also, remember that you're on display as well. Dress appropriately and don't distract from your cat -- remember, he's the star. Make sure to bring all the cat's paperwork, including shot and vet records, as needed for registration.
Perhaps the most important thing to do is to get a copy of the competition rules and regulations ahead of time. There are many cat fancy organizations, each with its own standards. Your domestic shorthair might be a better fit with some of them and a worse fit with others.