(this post is also in the Chuckwalla and Horned Lizard forums)
The issue of captive herp UVB requirement has been called a debate, although I’m not satisfied it ought to be. I’m convinced that captive herps do need UVB, in adequate doses and intensities. As I try to achieve acceptable quality of life for my captive animals, I research literature and interview professionals in herpetoculture. After a lengthy review of UVB lighting, I have some thoughts to offer:
Accepting for the moment that UVB is to be provided, what is a good source? I have read reviews of several UVB bulbs at reptileuvinfo.com and uvguide.uk, two thorough sources of information on the subject. Readers can learn the theoretical value of UVB, the potential risks of lamps that produce more UV in the 320 nanometer range than in the desireable 295-310nm range, and comparisons of lamps to natural UV intensities. These sites also discuss something I believe to have good potential for judging the amount of UV exposure needed; a reptile’s native ability to detect and respond to UVB radiance, and regulate its own exposure according to its instincts and cravings. As there is currently little published on the most desirable total amounts of daily UV for various groups of herps, it’s most convenient that herps do detect UVB and self-regulate their exposure, once given access to adequate levels.
“Adequate levels” is an important ingredient to success, as animals exposed to insufficient levels of duration, intensity and wavelength will continue to bask, trying to achieve sufficient exposures. It is difficult to assess the effectiveness of the UV offered to captives when they do not abandon their basking sites spontaneously after a certain exposure. If we have animals that leave the basking area before the lights turn off, we can hope that they have satisfied their requirements for the while; if they stay, we can’t be sure if they are unsatisfied or just content to sit there. By this logic, I’m suggesting that the best way to believe that a basking herp has received enough UVB exposure for the day is to see it leave the UV basking site before the light turns off, and rely on the herp to self-regulate its exposure.
Quoting from the introduction to Jukka Lindgren’s article on UV bulbs (IMO, a Must Read): “Vitamin D3 is photosynthesised in the skin of terrestrial vertebrates and birds by the action of UVB radiation on 7-dehydrocholesterol (7-DHC). This steroid is most sensitive to radiation in the range of 270-305 nm (fig. 1. MacLaughlin et. al., 1982). This range coincides with the lowest wavelengths of sunlight that can actually penetrate the atmosphere, the lower limit of the active range being 290 nm. While absorbed by a 7-DHC molecule, the UVB photon opens the ring structure of the molecule and converts it to a precursor of vitamin D3 (preD3). Subsequently, this is thermally isomerised slowly, over several days, to cholecalciferol that is the actual vitamin D3.”
I also call attention to the link to Brames; Aspects of Light and Reptile Immunity, linked from reptileuvinfo.com, and the links to the review of commercial UVB lamps by Lindgren, accessed by starting with uvguide.uk, then go to lighting survey intro page, scroll down to a link to Lindgren’s page and from there use the left menu to find the heading, “D3 Yield Index”. In summary, Lindgren rated what he called the D3 yield index of several commercial bulbs. By D3 yield index, Lindgren meant a bulb’s ACTUAL ability to stimulate the production off D3 precursors in skin (in this case, the skin of reptiles). From the abstract of the review: “The proportion of radiation energy that takes part in the photosynthesis of vitamin D3 was determined and the D3 Yield Index was calculated. Significant differences as large as thousand fold were found in the D3 Yield Indices. It is concluded that the percentage of UVB radiation from the total radiation figure does not necessarily give a true indication of a lamp’s capability to maintain cutaneous production of vitamin D3.” I currently accept that the D3 yield index is an important, if not the most important measure of a bulb’s value in maintaining D3 related health in captive herps, because:
Wavelengths above 320nm have been argued as causing photodestruction of D3, and some commercial lamps produce more UVB above 310nm than in the active range of 290-310nm, possibly resulting in the unintended destruction of more D3 than they synthesize. Again, quoting from Lindgren; “The spectral characteristics of light in the UVB/UVA range are an important factor in vitamin D3 photosynthesis. While 7-DHC is sensitive to irradiation up to 315 nm, cutaneous vitamin D3 that has been photosynthesised or obtained nutritionally is destroyed (italics added) by radiation up to 330 nm (Webb et. al., 1989.) This makes any radiation in the range 315-330 nm highly undesirable for the synthesis of vitamin D3.” Lindgren’s study was specifically the output of commercial bulbs in the 290-310nm range The short of it is that Lindgren gave the Zoo Med bulbs the highest D3 yield index, but I hope you will read the articles for yourself.
Once I had accepted Zoo Med bulbs as my bulb of choice, I returned to the uvguide.uk, and read the spectral spread charts to determine the effective distance from the basking site to set the bulb. I used the compact Zoo Med 10 bulb, mounted in a reflector cone with spring clamp from any lighting section of a home center or hardware store. To test the efficacy of the system, I needed some lizards.
I lived in Arizona for over 30 years, and I know that the radiation on desert basking sites is intense. Desert lizards have black perinea, the membrane that surrounds the internal organs, while more temperate lizards have transparent perineal membranes. Yes, that’s what I said. Desert light is so intense, lizards there have to shield their internal organs from it. My thinking was that if I could stimulate normal behavior and healthy growth in desert lizards, these results would, if un-empirically, demonstrate value in an artificial UVB source. I purchased some Side-Blotched Lizards (Uta) from a reptile show as test animals.
I have many years of experience observing and keeping Uta, which are native to Arizona’s deserts. My purchased animals were predictably stressed, dehydrated and hungry. I hydrated them with a soaking in shallow, warm bottled water for a few hours to allow cloacal uptake of water, an effective way of hydrating herps, especially small lizards. The Uta were provided a basking spot with appropriate temps and exposure to a UV bulb, placed so as to offer exposures of between 60-150microWatts/cm2, depending on which site the lizards chose (from a stack of small stones from 11 inches). The Uta were given a mix of insect prey including fly larvae, crickets, mealworms and fruit flies from a pet shop (crickets and mealworms are fed ground gamebird laying mash, which is richer in calcium than simple bran meal), and wild prey including small centipedes, ants, spiders and moths. Additional calcium is provided by dusting prey with pulverized eggshells several times a week (a superb herp vet once suggested leaving eggshell fragments in the cage with collared and leopard lizards, and to my surprise, the lizards did indeed spontaneously eat them from time to time. Reptiles need calcium in the form of calcium carbonate, as do prey insects in order to increase their calcium content, and powdered oyster shell and eggshell are sources of calcium carbonate). All the Uta soon behaved much as I have seen wild ones do, and a have bred in their enclosure. The eggs have not yet hatched, but a final evaluation of the UV bulb will, IMO, be the successful raising of healthy Uta from hatchlings. Of course, the bulb is hardly the only issue; diet is also crucial, but I believe that an effective UV source is one critical element in providing quality care.
. However I was interested in "fed ground gamebird laying mash, which is richer in calcium than simple bran meal." I never heard of this practice and it seems interesting to use as a gutload. What does this mash contain? Do you use it for all of your herps?