The coats of dogs share important features in common with the coats humans wear to keep warm. Dogs all have either single or double coats. Double coats are like our winter coats with an interior insulation layer to prevent loss of body heat and an outer layer to block wind and rain. Dogs with double coats generally have a soft, dense undercoat and a coarser, slick, weather-repellent top coat. Single-coated dogs lack the dense, insulating undercoat. They wear the equivalent of your lightweight spring jacket.
How do you know if Rover has a single or double coat? If he's not nearby, you can find out by looking at the standards for his breed. The American Kennel Club website offers the standards for all AKC-recognized breeds, and other kennel clubs and breed organizations do the same. The breed standards describe in detail the accepted coat types. If Rover is nearby, you can simply part his coat and look at the hairs. If you see long, harsh hairs combined with soft, downy fur, you know you have a double-coated dog. If there are only even-looking hairs with no soft undercoat, you own a single-coated dog.
Once you have identified a single coat, you can look further to determine the exact type of single coat it is. Some single coats may have hairs of different lengths, some short, some long. The texture of the hairs may also vary. Single coats may be straight, smooth, silky, curly or wiry. Poodles have a single coat of harsh, curly hair, while Maltese have a long, silky single coat; a soft-coated wheaten terrier has a soft, wavy single coat
Dogs with single coats enjoy some advantages when compared to double-coated dogs. One big advantage, much appreciated by allergy sufferers, that the absence of an undercoat means less shedding. Single-coated dogs do not blow their coats profusely twice a year; rather, they tend to shed in small amounts year-round. Another great advantage is that some short-haired single coats are very easy to groom.
Single-coated dogs mostly originate from areas with warm climates, where undercoats are not a great advantage. Chihuahuas, Afghan hounds and Salukis will struggle to keep warm in a colder climate. Just as you will be chilled wearing a light jacket in wintry weather, single-coated dogs need protection against loss of body heat when temperatures plummet. Long-haired single coats also are prone to matting, because dead hairs are likely to get caught in the coat; some can be more challenging to groom than any double coat.
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