Mutt's Day
Mutt's Day is held on July 31. By definition a mutt, sometimes called a "Half-breed", is a dog that is of mixed breed. This event in the third decade of the month July is annual. 
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Mongrels cost less to adopt than purchasing a purebred from a groomer. Estimates place the prevalence of mongrels at 150 million animals worldwide.
Mongrels can have a very individual and cute appearance based on the mix of different traits from the various breeds included in their makeup. Mongrels are often less prone to some health concerns since there isn’t as much inbreeding as you find with purebreds.
National Mutt's Day, also known as National Mixed Breed Dog Day, was created in 2005 by Celebrity Pet & Family Lifestyle Expert and Animal Welfare Advocate, Colleen Paige and is celebrated on both July 31st and December 2nd.
Similar holidays and events, festivals and interesting facts
No Pet Store Puppies Day on July 21
Get Out of the Doghouse Day on July 21 (The original idea came from the symbolism in the 1911 Peter Pan novel written by J. M. Barrie in chapter16 when Mr. Darling goes out and sleeps in the dog kennel, remorseful of not paying enough attention to his family and allowing his children to be kidnapped);
Dog Day in Latin America on July 21
DOGust Universal Birthday for Shelter Dogs on August 1
International Assistance Dog Week on August 3 (Starts on First Sunday in August);
Spoil Your Dog Day in US on August 10
US & UK National Dog Day on August 26 (was founded by a woman - Colleen Paige - in 2004);
International Dog Day on August 26 (supported by the International Fund for the Protection of Animals)