Doses and guidelinesThe following information is designed to help you create a better, more balanced diet for your tortoise. Sources and formulas are given at the bottom.
Formulas and sources
1. Length/Weight: SCLcm3x0.191=WTgr, or the 'Straight-line Carapace Length' in centimeters, cubed, times 0.191 gives you the predicted weight in grams. If the tortoise is lighter than the predicted weight, it is probably dehydrated. You can learn more about the formula on the 'Healthy Weights' page. (Donoghue)
2. Daily Caloric Need: WTkg0.75x72=KCalories, or, the weight in kilograms, to the 0.75th power, times 72 gives you the estimated daily calorie needs for an active tortoise. This would be reduced for an inactive or not growing tortoise (recovering, aged, winter time torpor, etc.) or increased for a very active tortoise (mating, nesting). (Mader, p.253)
3. Ratio of Calories from Fats, Proteins, and Carbs: 'H' is for 'herbivorous', and 'O' is for 'omnivorous'. Omnivorous reptiles should get about 50% of their calories from carbs, and 25% each from fats and proteins. Herbivorous reptiles get 75% from carbs, 20% from proteins, and only 5% from fats. (Mader, p. 255)
4. Calcium: 1.3 to 8mg x Kcal (or, for every Calorie of food, there should be 1.3 to 8mg of calcium). Phosphorous should be between 0.5 to 1 times the calcium dose. (Mader, p. 287)
5. Vitamin A, D, and E Ratios: The basic formula is a ratio of A:D:E of 100:10:1 (Davis)
6. Vitamin D dosage: (Source: Mader, p. 1069) Formula for mammals is 10-20IU/kg of body weight a day. Since reptiles have roughly half the mammal's metabolism, using 1/2 of that dosage 5-10IU/kg/day seems to work well. Vitamin D toxicity is rare, and most often seems to occur when over 50 times the recommended dosage is given for weeks at a time. The primary symptom of vitamin D overdose is calcification of the soft tissues. Vitamin D toxicity is not an issue when the D is delivered by UVB lighting.
Note: Numbers and dosages have been rounded. I cannot guarantee that the math or application of the formulas is accurate- just the best I can do.
Updated- Mark Adkins (C) 6-8-2012