Is there any previous research about the benefits of UV light in captive snakes?

Hello,

I am a veterinary surgeon researching the use of UVB lighting with reptiles and amphibians (also mammals and birds). The papers cited by Dr. Ott are very relevant and worthy of a little discussion.

1. Any wild animal which exposes any part of its body to daylight (daylight, not necessarily direct sunlight) will be exposing that skin to at least some UVB. Many diurnal snakes bask openly in direct sunlight; others "mosaic bask" in dappled sunlight through foliage. Many crepuscular and nocturnal species do emerge during daylight hours, if only for very brief periods; even more species sleep in sheltered positions (such as tree branches and crevices in rocks) where daylight does reach them, albeit in small amounts. Therefore in the wild, there is almost always the opportunity for a snake to receive UVB, and to use this free natural resource to synthesise vitamin D3 in the skin.

The study by Ferguson et al (2010) describes the measured daily UVB exposure of five species of snake, all of which were considered either as crepuscular or shade dwellers, or partial sun/ occasional baskers. The authors conclude that providing suitably low levels of UVB to reptiles with similar exposure patterns would replicate their exposure in the wild. This paper does not, however, establish whether snakes do synthesise vitamin D3 in the skin... only that the species they followed in the wild definitely had the opportunity to do so.

2. Nature typically utilises free resources very effectively; we should not be surprised if it turns out that very few snake species are unable to synthesise vitamin D3 in the skin under natual UVB light. The first study to demonstrate this is the one cited, by Acierno et al. (2008). Corn snakes were offered very low-level UVB exposure and responded by vigorous elevation of vitamin D3 levels, as indicated by their 25(OH)D3 status.

The second study cited - Hedley & Eatwell (2013) - was unable to demonstrate elevation of serum 25(OH)D3 in an all-female group of 6 ball pythons given quite intense UVB exposure daily for 70 days. A control group, (mixed males and females) not supplied with UVB, also showed little change in 25(OH)D3 levels over the same period. However, there were some very curious features about this study. All the females in the experimental group (a batch from one owner) had extremely high 25(OH)D3 levels initially, compared to the control group (a batch from another owner) so the groups were not comparable from the start. Also, the females in both groups had far higher 25(OH)D3 levels than the males, both at the start and the end... the authors discuss the possibility of egg production stimulating raised serum 25(OH)D3 levels in these females. This surely raises the question as to whether, if vitamin D3 synthesis was indeed occurring in the females given UVB, any extra produced could have been transferred to developing eggs - which require high levels of vitamin D for embryonic development.

Of course it is also possible that ball pythons do not synthesise vitamin D3 from UVB, but obtain all they need from their diet. Very high serum 25(OH)D3 in the experimental group, initially, before they had ever experienced UVB, clearly indicates that dietary supplementation with D3 works in this species!

It is also possible that these high serum levels inhibited formation and/or absorption of more D3 under the influence of UVB. Cutaneous synthesis is a self-limiting process in which, when the vitamin D binding protein is saturated, excess formed in the skin is "recycled" into apparently inert byproducts, owing to an equilibrium reaction dependent upon the wavelengths of UVB (and some UVA) present in the light....

As the authors themselves suggest, this study poses more questions than it answers, and hopefully further research will be done.

3. The paper by Chang & Zheng (2003) is quite different. They exposed the snakes to high doses of un-naturally short-wavelength UVB (from 290nm, peaking at 297nm, which means the UV contained considerable amounts of non-solar UVB) and examined the skin damage this rapidly produced at all but the very lowest exposure they trialled. The radiation they used was totally abnormal, and tells us nothing about the effect of exposure to natural "sunlight" levels. The authors conclude: "These results indicate that the skin of Cope's rat snake is more resistant to UVB irradiation than human skin partly due to a higher abundance of keratin."

By my calculations, the total UVB exposures causing damage ranged from 41.6 µW/cm² to 111 µW/cm², for 2 hours. Had this been sunlight, I think it is likely that little or no damage would have been caused. However, I strongly suspect that the UVB source with the described spectrum was a "phototherapy lamp", using phosphors similar to those causing severe skin damage in reptiles as reported by Gardiner et al (2009).

Gardiner DW, Baines FM, Pandher K. 2009. Photodermatitis and photokeratoconjunctivitis in a ball python (python regius) and a blue-tongue skink (tiliqua spp.). J Zoo Wild Med, 40(4):757-766

The high proportion of short wavelength UVB renders the radiation from these lamps much more harmful than the equivalent µW/cm² from sunlight. When I tested lamps of that type for that paper, I found that 100µW/cm² from one of the lamps was equivalent to UV Index 10.2 (Full tropical late morning sun)

For comparison, 100µW/cm² readings in sunlight are typically equivalent to approximately UV Index 1.5!

The snakes' resistance to such strong irradiation, however, does indicate that Cope's Rat Snakes are very tolerant of natural sunlight - which might imply that in the wild, they do expose themselves to it....

At present I am not aware of any other published studies on vitamin D3 in snakes. There have been several studies on UVB transmission through snake skin, indicating that transmission varies with likely exposure to sunlight: the more crepuscular the snake, the more transparent its skin to UVB - perhaps we can speculate that, like lizards, those that don't get much sun will have optimised the UVB penetration to ensure synthesis from very low UVB levels....

As regards other effects of sunlight / UVB exposure...anecdotal evidence is widespread about snakes selecting UVB lamps and "going crazy" to access them; increases in activity; changes in day/ night behaviours... all of which seem feasible if only as responses to UVA, which most snakes can see...

The only two scientific studies I can think of, are unpublished university dissertations.

One was one conducted simultaneously at ZSL London Zoo and Chester Zoo, in which groups of Jamaican Boas were exposed to gentle daytime UVB vs. "no UVB". Jamaican Boas, a crepuscular species, were found to be more active during the day when provided with UVB light, although this was not statistically significant. They did however, show statistically higher activity levels during night time observations (Bellamy & Stephen, 2007).

Bellamy, T., & Stephen, I. (2007). The Effect of Ultra-Violet B (UVB) Illumination and Vitamin D3 on the Activity, Behaviour and Growth Rate of the Juvenile Jamaican Boa Epicrates subflavus (Unpublished master's dissertation). University of London, United Kingdom.

Another found somewhat similar results in corn snakes (Nail, 2011)

Nail, A. (2011) Does exposure to UVB light influence the growth rates and behaviour of hatchling Corn Snakes, Pantherophis guttatus? (Unpublished master's dissertation). Reaseheath College and University of Chester, United Kingdom.

She wrote: "In conclusion, this study shows that snakes will voluntarily expose themselves to UVB light and that it has a positive effect on their activity levels. UVB exposure of 2% saw a notable difference in behavioural activities when compared to the other two groups in this study."

As regards lamp choice:

There is no need to use high-intensity UVB sources with snakes - indeed it would seem highly undesirable for most species, given their typical behaviours in the wild. Lamps such as the immensely powerful 300watt Osram UltraVitalux (minimum suitable distance for full sun baskers ~ 1 metre) would rarely if ever be appropriate. There are some very good sources of very gentle UVB now available to hobbyists, which have "safer" spectra with no abnormally short-wavelength UVB. Examples would be some of the T8 (1" diameter) fluorescent tubes, such as the Zoomed Reptisun 5.0 or the Arcadia D3 6%UVB ... or for even gentler UVB, the Arcadia Natural Sunlight 2%UVB. (NB. most other "natural sunlight" or "daylight" tubes, most being triphosphors for visible light, emit no effective UVB for vitamin D3 synthesis).