I doubt anyone can answer this question. There is very limited research out there on the physiological and dietary requirements of tortoises or on tortoise specific toxicity. There is limited funding available for these kinds of studies. I would suspect selenium needs are specific to individual species, so even if numbers had been determined for one tortoise species they wouldn't necessarily be relevant to another.
As keepers, it is our duty to provide the best diet that we can. Outside of those living near the native range of the species they keep, few have the ability to mimic natural diets so we make due with what we have. There is evidence from stool samples that several forest and forest adjacent species eat many kinds of mushrooms, so we offer mushrooms in captivity. Ideally, we should offer a wide variety, because we don't know how close the food we are offering is to the native alternative. We don't know why they eat mushrooms (what nutritional value they are seeking) so it's hard to say what species and varieties of mushrooms are better. Are they eating mushrooms for vitamin D? Minerals? Something else? We don't know. So we offer a variety and hope if they eat a little of everything they get what they need without getting too much of something harmful.
This is the same with offering animal protein. We know that there is observational and fecal evidence of red footed, yellowed footed, elongated, etc. eating animal carcasses that they come upon but we don't know what specifically they get from this. Is it just for the calories or range in amino acids or something else? Bacteria to aid in digestion? Some vitamin they don't synthesis themselves? Because we honestly can't answer most of these questions, keepers of tortoises that eat these complicated diets should just seek to offer diversity choices.
Some of the things we offer may be unnecessary, some may even be harmful if they ate them in excess, but a little bit of everything is what they get in the wild, and we don't have a better system in captivity. As far as I know, there have been no harmful effects documented from captive tortoises eating commercial mushrooms.
As keepers, it is our duty to provide the best diet that we can. Outside of those living near the native range of the species they keep, few have the ability to mimic natural diets so we make due with what we have. There is evidence from stool samples that several forest and forest adjacent species eat many kinds of mushrooms, so we offer mushrooms in captivity. Ideally, we should offer a wide variety, because we don't know how close the food we are offering is to the native alternative. We don't know why they eat mushrooms (what nutritional value they are seeking) so it's hard to say what species and varieties of mushrooms are better. Are they eating mushrooms for vitamin D? Minerals? Something else? We don't know. So we offer a variety and hope if they eat a little of everything they get what they need without getting too much of something harmful.
This is the same with offering animal protein. We know that there is observational and fecal evidence of red footed, yellowed footed, elongated, etc. eating animal carcasses that they come upon but we don't know what specifically they get from this. Is it just for the calories or range in amino acids or something else? Bacteria to aid in digestion? Some vitamin they don't synthesis themselves? Because we honestly can't answer most of these questions, keepers of tortoises that eat these complicated diets should just seek to offer diversity choices.
Some of the things we offer may be unnecessary, some may even be harmful if they ate them in excess, but a little bit of everything is what they get in the wild, and we don't have a better system in captivity. As far as I know, there have been no harmful effects documented from captive tortoises eating commercial mushrooms.
How much of what we eat do we eat for nutrition alone?
