New Notes on UVB: A little science behind vitD3 production.

tupinambis

Hi all. A while back I posted some observations I had with UV and tegu health, and while some people took my observations at heart for being just that, observations, others decided to attack.

Well, I've done a little more research into the field, and have found some interesting info you might like to hear.

For those of you with hand held radiometers, Gehrmann et al., 2004(1), indicate that they are unreliable and give varying readings that usually do not coincide accurately with actual values. You can use them for a general idea, but you shouldn't place any bets.

A little more interesting, is another paper by Gehrman et al., 2004 (2) that reports on UV ability to react with 7-dehydrocholesterol (pro D3) to form the photoproducts of previtamin D3 (preD3) and vitamin D3 (vitD3) in glass ampules (unfortunately, not live reptiles). In it they verified the reciprocity law (Parrish et al., 1978) that states that the UVB effect on photoproduct formation is NOT from irradiance per se (i.e. rate of energy delivery as watts) but rather the total energy delivered during a given time period, which is the dose [dose (mJ/cm^2) = irradiance X time/1000]. Essentially, longer term exposure to a low irradiance UVB source will create the same amount of photoproduct as a short exposure to a higher irradiance UVB source.

Next, the greater the concentration of UVB energy clustered around the MOST EFFECTIVE wavelength of 295nm, the greater the percent of photoproduct formed. Just because a bulb has UVB DOES NOT mean it will be effective at helping your animals produce vitD3, it has to have a good irradiance around 295nm.

And for a rather interesting result, when comparing standard bulbs of Reptisun 5.0, ESU Reptile Desert 7% UVB, a Sylvania 350 black light and a Westron mercury vapor spot lamp 160W for photoproduct production effectiveness, for similar doses, the BEST source is the Sylvania 350 BL, followed by the Westron mercury vapor, and the two specialist bulbs a dead last. For similar doses, the Sylvania 350 BL yields about 3X the photoproduct of the Westron, and about 5X the photoproduct of the Reptisun and the ESU Reptile Desert.

Keep in mind, however, that this study does NOT indicate what sources are best for a reptile, but given the findings of Ferguson et al., 2002, all these bulbs would be suitable, but the two reptile specific bulbs would have to be a lot closer to the animals to be as effective as the Sylvania and Westron for the same amount of time. In fact, given the irradiance of the Westron, it would be best kept at a good distance to avoid overexposure.

References

Ferguson, G.W., W.H. Gehrmann, T.C. Chen, E.S. Dierenfeld, and M.F. Holick, 2002. Effects of artificial ultraviolet light exposure on reproductive success of the female Panther Chameleon (Furcifer pardalis) in captivity. Zoo Biol. 21:525-537.

Gehrmann, W.H., J.D. Horner, G.W. Ferguson, T.C. Chen, and M.F. Holick, 2004. A comparison of responses by three broadband radiometers to different ultraviolet-B sources. Zoo Biol. 23: 355-363.

Gehrmann, W.H., D. Jamieson, G.W. Ferguson, J.D. Horner, T.C. Chen, and M.F. Holick, 2004. A comparison of Vitamin D-synthesizing ability of different light sources to irradiances measured with a Solarmeter Model 6.2 UVB meter. Herpetological Review 35: 361-364.

Parrish, J.A., R.R. Anderson, F. Urbach, and D. Pitts, 1978. UV-A: Biological effects of ultraviolet radiation with emphasis on human responses to longwave ultraviolet. Plenum Press, New York. 262pp.

Rick · Posted: Wed Apr 06, 2005 6:53 pm Post subject:

tupinambis,

Another interesting post. I also appreciate your extra time of supplying the resources from which the information was gathered.

Rick
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Sisco Reptiles - Proud Breeder of the Tamest & Most Social Tegus. See www.SiscoReptiles.com

herp_haven · Posted: Wed Apr 06, 2005 9:16 pm Post subject:

Good post. Thanks for the info.
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Tara
Reptiholic's Anonymous