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The miniature Jack Russell - is there such a thing? In truth there is no such thing as a purebred miniature. Anything that might be referred to as a mini Jack Russell is most probably a short legged Jack Russell or a crossbreed with some other miniature breed.
Many people are confused about what should be referred to as a mini Jack Russell. Realistically there isn't a type of dog that should be called a mini JRT. Most of the time what is really being referred to is a short legged Jack Russell. This is simply a Jack Russell that has been selectively bred for shorter legs. The rest of a short legged Jack Russell's body should be in the normal proportions of a full-sized JRT.
A true miniature is smaller in all its proportions than the full-size breed, not just in leg length. To achieve this a Jack Russell would have to be cross-bred with a smaller breed. But in this case the name "mini Jack Russell" doesn't really apply either - it's simply a Jack Russell mix breed. Be very wary of breeders who market their puppies as mini Jack Russells - chances are they don't know what they're talking about. The same goes for anyone advertising "teacup Jack Russells" - these are probably the result of breeding a series of runts to create smaller dogs. Steer clear of them.
The other possibility is that the dog is a dwarf Jack Russell, which is an indication of bad breeding. Dwarf Jack Russells tend to have a slight kink in towards the centre in their front legs. They also tend to have larger chests, so they are usually not even smaller than a regular JRT. They are often referred to as Puddin Jack Russells. They have a tendency to develop health problems, particularly arthritis in the back and joints.
Mini Jack Russell Mix Breeds
These are some of the mixes that may sometimes be referred to as a Mini Jack Russell. Be aware that many so-called toy dogs may also simply be the product of a line of runts bred together and may not be very healthy. Always do your due diligence and check out the health of the parent dogs before buying a puppy. Check out breed standards for size and don't buy a dog based purely on "cuteness" if it's obvious the breeder is only concerned about the money involved rather than breeding healthy pups.
Shih Tzu Jack Russell Mix
The Shih Tzu is a long-haired companion breed originally bred in China for royalty and the upper class. You can read more about the Shih Tzu Jack Russell Terrier mix here.
Toy Jack Chi or Jack Russell/Toy Chihuahua Mix
I would say the majority of puppies advertised as being "mini Jack Russells" are in fact mixes between a JRT and a Toy Chihuahua. You can read more about the Jack Chi here.
Jack Russell/Toy Fox Terrier Mix
This is another likely candidate when you hear someone talking about a mini Jack Russell. Fox Terriers and Jack Russells are closely related. In fact, up until relatively recently, there was no distinct "Fox Terrier" breed - the term Fox Terrier simply referred to any terrier used for fox hunting, so Jack Russells fell under this umbrella term. So this mix is the closest to being a true Miniature Jack Russell. There's more information on the Jack Russell Fox Terrier mix on this page.
Toy Jackapoo or Jack Russell/Toy Poodle Mix
These dogs tend to have a noticeably curlier coat than a typical JRT. If you ever hear of a "curly coat Jack Russell," it's probably one of these. Read more about the Jackapoo mix breed here.
More Essential Information
No matter what type of Jack Russell you may be dealing with it's important that you understand the specific training needs of the breed. Find out more about the ins and outs of training Jack Russells in my free special report.