Vitamin D and Dogs
Sunlight and longer days of exposure (spring) create the hormone that is vital to animal estrus including canine heat cycles, healthy gestation and puppies.
IMPORTANCE OF VITAMIN D FOR DOGS
A doctor in India who is a GSD fancier asked me about shedding, heat cycles, and what specific hormones are stimulated by shorter days of sunlight exposure.
It’s been about 55 years since I took courses in polycyclic compounds and biochemistry but I surmised that a combination of endocrine, exocrine, and paracrine hormones causes the changes in coat growth and replacement in response to the amount of sunlight (vitamin D) the animal is exposed to.
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It is difficult for some people to balance the amount of sunlight and hormone production. Too much and we get sunburned; too much when we are children increases our risk of late-developing skin cancer; too little and we don’t make enough vitamin D out of the biochemicals we manufacture or get from our food. Dogs also can have adverse effects from solar exposure, depending on breed, skin pigment, and haircoat. Or they can be deficient when living indoors, in shade-starved cities, dark jungles, or Arctic tundra. Either way, the amount and intensity of sunlight profoundly affects canine hair, skin and body function.
The primary protection dogs have from too much solar exposure is simple: shade. Dogs do not perspire through the skin as we do, but instead regulate body temperature by getting out of direct sunlight, wallowing in water, decreasing activity, and panting. In fact much heat is taken from the lungs by panting - you see the condensation dripping from their tongues- because evaporation is the primary method of cooling whether through sweating or panting.
Surface color in most dogs is primarily that of the haircoat. If you were to shave a lot of dogs or look at hairless varieties, you might be surprised to find what colors the skin will show. Owners of many short-coated dogs, especially white ones, frequently see mottled or spotted skin colors in various shades of pink, grey, black, or even bluish or brownish hues. Some reports indicate that white dogs such as some Boxers and various Bulldog breeds have a much higher incidence of skin cancers than do dogs that have more dark-hair coat and perhaps more skin pigmentation. Protection often seems to be a combination of hair and skin pigment.
“Fur” or "coat" is usually used in reference to mammalian haircoats but we also use “pelt” for the complete hair and skin of an animal. Adult canine fur/coat usually has three types but breeders usually just talk about topcoat and undercoat. There are the shorter down-like hairs (fuzz), longer and stiffer guard hairs, and medium awn hairs which are shorter than the guard hairs but longer than the extremely fine down hairs. The awn hairs help with insulation and protect the downy layer underneath. Most of the visible coat is made of this kind of hair, especially in the softer-coated breeds. The harsher the texture, the more you are feeling the guard hairs. Even in the so-called hairless breeds, there is some fuzz somewhere, and often there is longer hair as in eyebrows, a crown crest, and/or tail feathering.
I have been fortunate to have lectured and judged dog shows in at least 30 countries and have observed many breeds that many dog fanciers will never see. Some are hairless types such as the Peruvian Inca Orchid. The American Hairless Terrier is the only hairless breed that is a result of a recessive gene. It was split off from the Rat Terrier genetic pool many years ago by national kennel clubs. Unlike the hairlessness resulting from dominant genes, the AHT has no dental, skin or other health issues associated with the dominant gene in the other hairless breeds such as the Chinese Crested, the Mexican Hairless, the Bolivian Khala, and the Peruvian dog. Even these breeds have furry individuals, useful in maintaining health, dentition, and newborn viability.
The Role of Vitamin D In The Canine
Animals evolved or were created with fur or hair that prevented too much ultraviolet light from damaging skin and eyes, or having other bad effects on health. But the evolution of cars and indoor working environments took us too far in the other direction, preventing humans (and to a great extent, their house pets) from getting enough direct sunlight. Glass (windows) block ultraviolet light while allowing infrared in. While we animals actually manufacture Vitamin D, we do need both its dietary precursors and some UV radiation in order to synthesize Vitamin D.
This steroid/hormone is required for optimum health; Vitamin D protects against osteoporosis and helps in absorption and regulation of calcium (needed for bone, muscle, and nerve tissue production and function), ensures proper thyroid function, and assists with blood clotting, metabolism, brain development, insulin production, control of inflammation, and heartbeat rhythm. It also influences the immune system and secretion of insulin. And D can actually help to significantly reduce your risk of other types of cancer.
A little more detail might be of interest: a Vitamin D precursor molecule called 7-dehydrocholesterol (7-DHC) in the skin is converted by UV in sunlight to the vitamin. That is then metabolized in the liver and kidneys and sent via the arteries for use by almost all the body’s cells.
Importance of Vitamin D In The Canine Diet
Dogs receive some Vitamin D via sunlight exposure but dietary sources are much more important to canines because of some major differences in cell biology compared to us humans. Even then, carnivores such as dogs seem to have much lower D requirements than other fur-bearing animals, and do not synthesize nearly as much via sunlight exposure as other furry herbivores and omnivores do. Comparatively, dogs have very low levels of precursor 7-DHC in their skin—rats have 950 percent more than dogs.
Some researchers theorize most 7-DHC in dogs is converted to cholesterol before it can be converted into Vitamin D. This lack of significant skin synthesis leads to the suggestion that dogs satisfy the majority of their D requirements through diet. The organs of prey animals that canines normally feed on are very high in Vitamin D content, and a good commercial or home-prepared dog ration will include such sources. Dogs and people can get Vitamin D from oily fish such as salmon and tuna, and a little from margarine, milk, and eggs.
We animals get calcium from food or supplements but it does almost no good unless Vitamin D is there to absorb it. A general but flexible rule to reduce risk of calcium and Vitamin D deficiency is daily exposure to direct sunlight and assuring Vitamin D-rich foods. Our dogs need sunlight exposure for other reasons besides 7-DHC synthesis and metabolism. Depending on breed, to some extent, direct or indirect incidence of sunlight (not behind glass) affects estrus timing, undercoat development, and non-estrus-related hair shedding.
I am not an endocrinologist but when it comes to productive breeding cycles and overall health, unfiltered sunlight is important. Those who live in tropic or near-tropic climes will see that, as a rule, their dogs will have less undercoat and will shed more or less constantly rather than completely “blow” their coats twice a year such as the Shiba, Basenji, Telomian, or other close relative to the wolf.
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Fred Lanting is an all-breed judge with experience in over 30 countries. He is a well-known Shiba breeder and GSD authority. He handled Akitas in the 1960s and `70s, and was named an official JKC judge, a rare honor. He has lectured around the world on breeding, judging, canine movement, and CHD (canine hip dysplasis). Be sure to peruse these Dog Books by Fred Lanting