After reading a reply about the oxalic acid levels in plants tortoises feed on in their natural habitat, I'd like to hear your views as to whether you limit feeding plants with moderate / high levels. I've always tried to limit them as much as I can, but now thinking about how neccessary it is. My reasons for this have been due to oxalic acid binding with the available calcium in a foodstuff, so the more oxalic acid the less calcium available. I also thought that bladder stones were a result of a diet high in this. I've read in the past that vit A offsets the effects of the acid, but I'm not 100% sure as to where I read it or how true it is. If additional calcium is added, and a vitamin supplement like nutrabol alongside regular soakings for hydration, is there a need to avoid these foods?

Thanks Jo

Good question - and one I would like the answer too.

I wonder in the calcium content to oxalic acid ratio of a foodstuff would be more useful than a figure for the oxalic content of a plant alone? also there are different types of oxalic acid in each plant and there is research available that suggests that the percentages each type present is more important than the overall oxalic acid content.

hi now this is an interesting subject.oxalic acid is the bogey man among tortoise diets.whenever i have inquired about the values of available wild plants i always seem to get the same reply"feed in moderation or avoid at all costs contains oxalic acid.i often wonder about the nutritional value of things that are available when all else fails .very early spring i see a lot of sheeps sorrel about but avoid it because "its got oxalic acid"another. creeping speedwell i need to be desperate to feed it sparingly.i wonder as part of a balanced diet would it actually be beneficial to add small amounts to the diet.some plants contain trace elements that might otherwise be missing from the diet.it would be marvellous to be able to access a database listing all these common wild plants giving a detailed breakdown of their content.i realise certain aliments in the plant are gleaned from the soil in which they grow but even then there must be a basic content.sorry i went off on one then,you got my attention.

I would have thought that tortoises in the wild, ate food as it came into season. Some weeds/plants being available at different times of the year.
When I first kept tortoises, I couldnt understand why they would eat plants at one time of the year and not another. I am sure this is down to plants being in season. This is partly how they have a mixed diet. Not really mixed diet every day. But I could be wrong. I have never worried too much about how much of what my tortoises eat. I try not to feed the same food for long periods. I am sure sometimes we get to technical and in depth at what tortoises eat. But thats just me.
My tortoises remain healthy so I dont worry. (fingers crossed I am not tempting fate:0) )

My understanding is that Oxalic Acid binds Calcium into Calcium Oxide, a form of calcium which is not metabalised by a tortoise. As it's essentially a waste product its stored in the bladder, which for a tortoise is a receptical for waste products as well as the bodies water reservoir. The tortoise will release these waste products in one of two ways, urine if the tortoise is in a position to replenish its water reserves or as solid urates which are a tortoise means of expelling waste from the body when it is not in a position to replenish its water store. The urine/urates production takes place in the bladder so I personally feel good hydration is key. The stones encountered in tortoises form in the bladder and are composed of calcium oxide so it makes sense to me to regularly allow the tortoise to drink and ensure that its housing conditions do not place it in a state of constant dehydration. Indoors, in centrally heated rooms with lamps too means that just by the act of breathing the tortoise is losing tiny amounts of water constantly. I often see reports of gritty urates or even stones being passed throughout the winter.

I think I avoid the issue of Oxalates through varity rather than never offering plants with known high levels of oxalic acid. I'm unsure as to whether high calcium levels override lesser amounts of oxalic acid leading to some useful calcium metabolism. I asked a question on the TT forum regarding usable calcium content of Opuntia cactus as mpst of the available calcium is tied up in an oxide and the consensus was that it would be available to the tortoise to a degree due to the volume of calcium available. Of course without vitamin D3 no calcium can be utilised and I wonder if, in the presence of oxalic acid, this would be a contributatry factor in the formation of stones.

I have read a few fleeting remarks in articles that tortoises (specifically Testudo) have mechanisms to deal with oxalates. Joanna, I'm interested in the link to vitamin A if you can recall where you saw it. Vitamin A is present in all plants as far as I'm aware. Its amazing how many calcium rich plants also contain oxalic acid, if vitamin A in some way negates the reaction between calcium and oxalic acid there may be some complex balancing act ( chemically) going on that allows the tortoises to graze these plants.

Apologies if I've got some of my oxides and compounds mixed up, its rather late

Good to hear all your views/ opinions. Claire, I was chatting to someone online who believes its more to do with the ratio between calcium and oxalic acid. He offers spinach as in his opinion due to the levels of calcium there is still some available to the tort. Terry - I've noticed alot with mod / high levels do contain some beneficial nutrients and often wonder if they are missing out on some by avoiding feeding. Sandy, I've noticed that some weeds are eaten well and then later in the year not touched. Or only the new fresh leaves eaten and not the old - not sure if this is just down to taste, or if levels of nutrients / oxalic acid change throughout the year? Dave, interesting post. I think I'm understanding it a bit more now. I will have a search for the vit A info, I will have a reference to it somewhere here. I'm away for a few days but will hunt it out next week.

The trouble with ratios of calcium to oxalic acid is that you have to consider actual amounts too.

By my figures (keeping a database of figures - amounts are only entered once I have three seperate values from three sources so that an average can be taken, then ratios worked out with my dodgy maths!) spinach has the same ratio of calcium to oxalic acid as romaine lettuce but thats because there is very little calcium in the lettuce.

From what Ive been reading high oxalic acid gives leaves a bitter taste to them and it increases in some plants when the leaves are older. In Dandylion for example, oxalic acid levels rise once the plant has flowered. So it wouldnt suprise me in the slightest if the clever torts refused to eat any leaves that are very bitter!

thats interesting information could this be because the flower has different properties to the leaves and should be avoided or just a change in the whole make up of the plant when flowering.i wonder was it just the leaves tested in both cases or just the leaves both times.

lol I dont have dandelions long enough for them to get old:0)
I have heard that the stalks of dandies have a high concentrate of OA.

yes i cant remember where i heard it so didnt want to say,i must admit i do tend to leave the flower stalks just to be sure.i will pick a big juicy flower head though if its there.