Supplementation is a controversial topic in captive tortoise care. Some keepers believe daily supplementation with calcium and multivitamins is very important for growing tortoises. Others feel that over supplementation is a real danger and find supplements totally unnecessary. The rest fall somewhere in between. They use calcium and vitamin supplements, but not daily.
If you are sure your tortoise's diet is spot on, which is very hard to do, he may not need any vitamin supplementation. However, ensuring adequate calcium, mineral, and vitamin intake is important for tortoises, especially for young, rapidly growing ones and egg laying females.
Researchers are still trying to determine the ideal amount of protein in tortoise diets. Opinions and recommendations vary.
Now, protein measured on wet basis cannot be directly compared to protein measured in dry substance. For example, the protein content of dandelions is 2.7% on wet basis and 18.7% in dry matter (Star Tortoises, 2007).
Tortoise Trust mentions in one of their online nutrition articles that the safe upper protein limit in the diet would seem to be 7%. Wild tortoises typically eat about 2-6% plant protein on WET basis.
Dr. Hartmut Wilke comments in his book (My Turtle, 2009) that the ideal tortoise diet should contain 20% plant protein for adults and 24% for youngsters in DRY substance. Crude fiber content should be 12-30%.
According to Susan Donoghue, MS, DMD, DACVN (in Mader's Reptile Medicine and Surgery, 2006) most herbivorous tortoises consume diets that contain about 75% carbohydrates, 20% protein, and 5% fat. High fat levels, above 12%, can cause digestive upsets in herbivores.
If you feed your tortoises prepared diets, aka pellets, check the container labels. Choose products that are high in fiber, low in protein, and low in fat. Ideally, use them as a supplement only to cover any potential nutritional deficiencies.
For tortoise diets, the traditional recommendation for calcium to phosphorus ratio (Ca:P) is 2:1 at the minimum. A ratio of 5:1, or higher, would be even better. You can sprinkle some phosphorus free calcium carbonate powder on foods, especially if you use grocery store greens, to up the calcium content (see calcium info below).
Update 2012: Based on newer studies, the need for calcium in tortoises may be even greater than previously believed. For example, a recent study done on plants eaten by Egyptian tortoises in the wild revealed that the mean Ca:P ratio was about 14:1. The Ca:P ratio ranged from 3.92 to 32.44 (The Batagur #2, TTPG, 2012).
Who's been eating cuttlefish bone...? A Burmese star.
You can serve limestone flour loose or use it to make your own calcium blocks. I mix a small amount of water with the powder to create a paste. I put the paste into a paper cup, let it dry, and then rip off the paper cup.
1.) Reptile calcium supplements
Pet stores sell many different brands of reptile calcium supplements. I have used the phosphorous free, ultra fine Rep-Cal calcium powder (pic) for many years as my main calcium powder supplement.
During the spring, summer, and fall when all my tortoises are outside and synthesize their vitamin D3 from the natural UVB of the sunlight, I only use plain calcium and/or cuttlebones. For tortoises that stay indoors for mid winter, I occasionally use calcium powder with vitamin D3 during those months.
Caution! Products containing vitamin D3 should always be used very sparingly, if at all (use good quality UVB bulbs instead), because vitamin D3 can be dangerous if overdosed.
2.) Human calcium supplements
If you choose to use human calcium supplements, select a product that consists of pure calcium carbonate powder with nothing added. If your tortoise spends his days outside in the natural sun, he does not need vitamin D3 supplementation. Just plain calcium.
3.) Cuttlefish bones
I keep cuttlebones, aka cuttlefish bones or sepia bones, (pic below) in my indoor and outdoor tortoise enclosures as a self-help calcium source. This way my tortoises can nibble on them whenever they feel the need.
Cuttlebone is the hard, internal shell of a cuttlefish (a mollusc). Cuttlebone is mostly composed of aragonite, a naturally occurring form of calcium carbonate. You can find them in the bird department of your local pet store. Cuttlebones are also packaged as Turtle Bones, but at a higher price.
Cuttlefish bones freshly collected from the beach can have a somewhat fishy smell to them. Some tortoises may not like them. Soaking the cuttlebones for several days or leaving them outside in the sun and rain, or near sprinklers, for a a few weeks helps make them more palatable to many tortoises.
Before feeding, I sometimes peel off the hard backing for fresh hatchlings. I find that soaking the cuttlebones first for 24 hr makes the removal easier.
4.) Ground limestone
Another popular calcium carbonate supplement is finely ground limestone, aka limestone flour (pic above). Just put some flour in a shallow dish and allow your tortoises to snack on it at will.
You can find limestone flour in feed stores. It's sold as a calcium supplement for horses, sheep, and goats. If you buy limestone powder from other sources, check that it's food grade.
Loose limestone powder is very messy, but you can easily make your own calcium blocks with it (pic above). I mix a small amount of water with the powder to create a paste. I put the paste into a paper cup, let it dry, and then rip off the paper cup. I place the resulting calcium block on a small lid for feeding. My tortoises are not very fond of limestone flower though, they seem to prefer cuttlebones.
Caution! If you have asthma, be careful when pouring limestone flour. It is very fine, powdery, lightweight, and becomes airborne easily. You don't want to breath in this stuff.
Cuttlebones and popular tortoise vitamin & mineral supplements.
1.) Reptile vitamins & minerals
I have used Rep-Cal's Herptivite for a long time. It is a multivitamin, multimineral, and amino acid powder that has been on the market for many years.
Other popular supplements I have used include Repashy's SuperVeggie dust, Sticky Tongue Farms' Miner-All, and Carolina Pet Supply's TNT.
Miner-All is a human grade, phosphorous free, calcium based mineral supplement. Miner-All Outdoor formula contains no vitamin D3, but Miner-All Indoor version does.
TNT, aka Total Nutrition for Tortoises, consists of dried, powdered plants chosen for their nutritional value. It has been used for over twenty years and is available with or without probiotics. Carolina Pet Supply was one of the first reptile companies to sell dried herbs and seed mixes specifically for tortoises.
2.) Fortified foods
I also serve fortified foods like Zoo Med Natural Grassland food and Mazuri Tortoise Diet (LS or classic formula) several times a month as an additional nutrition source. I like to keep the pellet foods to less than 10-20% of the total diet.
If you feed these types of foods (see pellets) fairly regurlary, there is no need for additional multivitamin supplementation because commercial tortoise foods are vitamin and mineral fortified. Do provide additional calcium like cuttlebones though.
The frequency of my calcium and vitamin supplementation depends on the animal's diet, time of the year, and the stage of the tortoise. During winter, when my tortoises eat more store greens and less backyard weeds, I add calcium and vitamins to their diet more often. Also, the younger the tortoise, the more often I supplement.
Instead of powdered vitamins and minerals, you can also use commercial tortoise foods as supplements. I rotate between powder supplements and commercial diets; I don't use them together. A little bit of everything to round out the diet.
Calcium supplementation is especially important for babies, youngsters, and egg laying females. Young star tortoises, like all tortoise babies, need plenty of calcium for healthy bone development. In gravid tortoises, building egg shells draws a lot of calcium from the mother's reserves. It needs to be replaced in the diet.
For example, Sticky Tongue Farms' recommendation is to use their Miner-All reptile calcium & mineral supplement (see above) every feeding from babies to half growns, every other feeding from half growns to subadults, and every third feeding for adults. Food for egg laying females should be supplemented every other feeding.
A general recommendation from Simon Girling, a UK zoological veterinary surgeon (Pet Owner's Guide to the Tortoise, 2002), is to offer plain calcium daily. Multivitamins and minerals can be given twice a week for youngsters and once a week for adults.
Andy Highfield of Tortoise Trust (Promoting Proper Bone Development, 2003) recommends daily supplementation with phosphorus free, plain calcium and weekly supplementation with minerals. His recommendation for vitamin D3 varies. If your tortoises spend 3-4 hours outside daily and you live in an area that has wild tortoises, you probably do not need to supplement vitamin D3. Otherwise, provide a small amount of oral vitamin D3 about 2-3 times a week.
Caution! Use vitamin D3 containing products sparingly. Overdose of supplemental D3 can be toxic.