Vitamin D Synthesis In Furry Animals

[Travis]

I just had a real silly thought:

If Vitamin D is created from Cholesterol by UV light on the skin, then how do furry animals synthesize Vitamin D?

You would think that the fur would get in the way; right?

 

[Travis]

I just found an article, and it's kinda funny: Vitamin D(3) synthesis in the entire skin surface of dairy cows despite hair coverage.

How hair-coated animals such as dairy cows synthesize endogenous vitamin D(3) during exposure to summer sunlight has been unclear since vitamin D(3) and its relation to sunlight was discovered. The fur of fur-bearing animals is thought to be comparable to clothing in humans, which prevents vitamin D(3) synthesis in the skin during exposure to sunlight.

This is what I thought.

Different scenarios have been suggested but never tested in cows; for example, that vitamin D(3) is synthesized from sebum on the hair and ingested by cows during grooming or that body areas such as the udder and muzzle that have scant hair exclusively produce the vitamin.

Total snout-synthesis? I wonder who signed their name to that theory?

To test different scenarios, 16 Danish Holstein dairy cows were subjected to 4 degrees of coverage of their bodies with fabric that prevented vitamin D(3) synthesis in the covered skin areas. The treatments were horse blanket (cows fitted with horse blankets), udder cover (cows fitted with udder covers, horse blanket+udder cover (cows fitted with both horse blankets and udder covers), and natural (cows without any coverage fitted).

Udder covers? You'll probably never see this term mentioned anywhere, ever again.

The cows were let out to pasture daily between 1000 and 1500h for 4 wk in July and August 2009. Blood samples were collected 15 times during the study and analyzed for content of 25-hydroxyvitamin D(3) [25(OH)D(3)] indicative of the animals' vitamin D(3) status. Results showed that uncovered cows had a higher 25(OH)D(3) concentration in plasma after 28 d of access to sunlight compared with covered cows and that the plasma concentration of 25(OH)D(3) was strongly inversely correlated to the body surface area covered. These results are consistent with findings in humans, wherein the vitamin D(3) status of different individuals was inversely proportional to the amount of clothing worn during exposure to artificial sunlight. Hence, it appears that human clothing and cow hair are not comparable with respect to prevention of vitamin D(3) synthesis and that cows, like humans, synthesize vitamin D(3) evenly over their body surface. That vitamin D(3) should be synthesized from sebum on the hair and obtained by cows as a result of grooming is not supported by the findings in the present study either, because large differences were found between the treatment groups. If grooming were the source of vitamin D(3), then a relatively even 25(OH)D(3) concentration between treatments would be expected, because covered cows would obtain vitamin D(3) by grooming uncovered herdmates.

So it seems that the fur poses no real obstacle to Vitamin D synthesis. Maybe the sunlight actually penetrates the fur; or maybe the newly synthesized Vitamin D on the fur kinda diffuses back through the skin somehow....

 

[Giraffe]

I thought that animals get vitamin D by licking their fur. Have not checked it though.

 

[Luann]

Ears. Something about rabbits and their ears.

 

[paymanz]

What's the level of vitamin d in animals?

 

[Light]

As far as I know, light penetrates thicker things than hair/fur:
it supposedly goes through our hair+skin+skull to illuminate the brain during the day, which has an effect in producing Co-Q10 and probably other things as well.
Just think of putting a flashlight right against the palm of your hand, it makes the hand "glow" in red, and you can totally see it coming through.
Also, the wavelength that initiates production of vit D is ultraviolet, not in the visible range, so I think you can think of it like a radio wave or an X-ray - electromagnetic frequencies that easily go through us. They can have serious effects even though we don't see an X ray on the skin like we see sunlight.

 

[Travis]

Ears. Something about rabbits and their ears.

True that bunny ears do go flaccid during captivity, perhaps being the result of reduced collagen synthesis consequent of ascorbate deficiency. I could see how the more flaccid ears could collapse onto the relatively hairless rabbit snout—a hypothesized vitamin D synthesis 'hotspot'—and block a little ultraviolet light, yet at the same time their ears would produce their own vitamin D resulting in little-to-no net effect. The perkier ears are certainly a few centimeters closer to the sun, so you have that, yet their relatively hairless interiors could intentionally be directed by the rabbits towards the sun under low vitamin D conditions—somewhat akin to how a radar dish hones-in on longer wavelengths of the electromagnetic spectrum.

 

[Travis]

As far as I know, light penetrates thicker things than hair/fur:
it supposedly goes through our hair+skin+skull to illuminate the brain during the day, which has an effect in producing Co-Q10 and probably other things as well.
Just think of putting a flashlight right against the palm of your hand, it makes the hand "glow" in red, and you can totally see it coming through.

It has proven been proven that vitamin D₃ synthesis occurs despite hair coverage by the Hymøller & Jensen, two Danes that'd initially been under the illusion that cows' udders would be a primary source of dehydrocholesterol photolysis. Ostensibly they had not known that only rabbit ears have this property, via heat-directed ultraviolet light-funneling (Travis, 2018), and for this reason they had used custom-tailored 'udder covers' to mask this region (Hymøller, 2010). Whether-or-not their udder covers had nipple holes had not been mentioned, yet these would be somewhat easy to fashion using brass rivets and a leather punch.

Hymøller & Jensen. "Vitamin D₃ synthesis in the entire skin surface of dairy cows despite hair coverage." Journal of dairy science (2010)

'The treatments consisted of 4 different degrees of coverage of the cows’ bodies with fabric that prevented vitamin D₃ synthesis in covered skin areas. The treatments were 1) horse blanket: cows were fitted with Horze Eczema UV protection blankets from Horze (Hollola, Finland); 2) udder cover: cows were fitted with udder covers; 3) horse blanket + udder cover: cows were fitted with both horse blankets and udder covers; and 4) natural: cows had no coverage fitted.' ―Hymøller

'The treatments were horse blanket, udder cover, horse blanket + udder cover , and natural.' ―Hymøller

'At the end of the study (day 28), the 25-hydroxy-D₃ concentrations were 28.6 ng/mL in the natural group, 23.2 ng/mL in the udder cover group, 8.9 ± 1.8 in the horse blanket group, and 6.0 in the horse blanket + udder cover group.' ―Hymøller

'Vitamin D₃ synthesis in dairy cattle takes place in all areas of the skin and is not exclusively associated with skin areas where hair coverage is scant or lacking (e.g., udder and muzzle).' ―Hymøller​

As you can see from Table 2, the udder can only be assumed responsible for contributing between 3.69 and 38.60 percent natural vitamin D₃ synthesis in dairy cattle. The remainder must must be accounted-for by furry regions, yet since these cows had been Holsteins they could benefit by their snow-white hair surrounding their jet-black spots. Since black is defined as complete absence of light transmission, or its total absorbance, you'd expect the white hair surrounding the spots to admit more ultraviolet light in Holsteins. An analogous thing can be said about Dalmatians, and perhaps even panda bears. The white hair of the polar bear, arctic fox, and Siberian wolf are generally-assumed to have been evolved for camouflage—e.g. an artifice to allow for more efficient stalking of prey—yet this could also be expected to increase vitamin D₃ synthesis in low ultraviolet regions. Although arctic monkeys have very dark hair they do have large areas of fair skin.

'The theory that vitamin D₃ should be synthesized from sebum on the hair and obtained by cows as a result of self-grooming or grooming of herdmates is not supported by the findings of this study.' ―Hymøller​

Alternatively: Previtamin D₃ could be synthesized by the photolysis of 7-dehydrocholesterol on the hair shaft and subsequently absorbed, perhaps catalyzed by the thermal expansion of the sebum. This process could imply that dark hair would synthesize more hairshaft vitamin D₃, yet the lighter and more reflective hair may still act like a waveguide to direct light towards the follicle. Vitamin D₃ is known to be absorbed through the skin, and as a secosteroid it has a lower viscosity than cholesterol. The greater fluidity of vitamin D₃ relative to its steroid precursor could perhaps lend it a greater propensity for retrograde transport.

 

[paymanz]

Very nice Travis thanks