There is a large selection of miniature dog breeds to choose from and it is important to consider carefully the pros and cons of each breed to ensure you find a dog which suits your home and lifestyle. A few things to consider before you decide on a toy breed dog: Their very small size means it's more difficult for a veterinarian to treat a small breed dog than to care for a larger breed puppy. A toy-size puppy doesn't have much extra weight to lose and he will dehydrate rapidly. Toy puppies are predisposed to hypoglycemia (low blood sugar), although terrier breeds seem to be more robust.
Most of the small breeds are small counterparts of larger breeds. Some miniature breeds are both ancient and modern. Ancient because they descend from types of dogs that have been around for centuries; modern because some of them derived from a purposeful interbreeding of several breeds (e.g. Miniature Pinscher). At first glance the Eskie appears to be a miniature version of the Samoyed, but closer inspection reveals that the two are not proportioned the same. The Italian greyhound appears to be a miniature version of the Greyhound with all the talents of its big brother.
It is widely believed that pedigree dogs are very inbred, due to closed registries and breeding practices, and that this has had a detrimental effect on the health and welfare of many pedigree breeds. Indeed studies have determined a large depletion in genetic diversity in some pedigree dogs breeds], and many breeds do suffer a high burden of genetic disease. For example, the Cavalier King Charles spaniel, a popular miniature dog breed, is afflicted with as many as 29 diseases. The issue of inherited disorders and poor health in pedigree dogs has been widely discussed in recent years. With the advent of new technologies and the increasing development of new diagnostic DNA disease tests, the full extent and prevalence of inherited disorders in pedigree dogs is now being realized. However, with over 200 breeds officially recognized by the kennel clubs 396 inherited disorders currently identified, many breeds have reached the point at which successfully breeding away from susceptible individuals will require new genomic selection strategies. Please keep in mind, that all responsible breeders will always screen their stock for the diseases commonly seen in their breed and will make the results of those tests available to prospective puppy buyers.