UV Question

[vikki01]

Do tortoises only absorb uv light through their skin or can they absorb it through their shell as well? I am just wondering if the times they do not have head/legs out if they are getting any benefit. My two are prone to digging down a bit outside and sometimes only the top of their shell shows and was interested to know if they are getting any uv at these times, also sometimes when indoors they will be under their combi lamp but not necessarily with head/legs out. Many thanks.
Vikki.

 

[Tidgy's Dad]

They absorb UV light through the skin, not through the shell that is largely composed of keratin.
Unless they are totally withdrawn all the time they will get uvb and it is reflected too, to some extent.
This is why tortoises often stretch out fully their limbs and head, to get maximum skin area exposed.
However, they don't seem to require many actual hours of sunshine a week, maybe just one or two.
Probably more needed from a UVB light but I wouldn't worry myself.
I think my science might be slightly dodgy here so hopefully I've bumped the thread and someone more knowledgeable than I will confirm.

 

[vikki01]

Thank you, I am not really worried but just wondered out of interest as the skin seems such a small area and obviously the shell is affected by lack of uv/calcium so wasn't sure if it could also be involved somehow. One of my tortoises "Herbie" is very good at multi-tasking and soaks up some uv while taking a nap.

 

[Tidgy's Dad]

Thank you, I am not really worried but just wondered out of interest as the skin seems such a small area and obviously the shell is affected by lack of uv/calcium so wasn't sure if it could also be involved somehow. One of my tortoises "Herbie" is very good at multi-tasking and soaks up some uv while taking a nap.

He looks lovely.
Classic basking pose.
UV is necessary so the tortoise can synthesize the vitamin D3 in his skin which is involved in process of calcium absorption needed for healthy shell and bone growth.
As long as they spend time outside in the sun, then the UVB light is just a backup, they should be fine.

 

[Tom]

It is generally assumed that D3 synthesis takes place in the skin, as it does in other reptiles, but I don't know that it is conclusively, scientifically proven that it does not also happen in the shell.

For our purposes as tortoise keepers, it doesn't really matter. If they have adequate UV bulbs inside or get some regular sunshine outside, they will be fine.