This post from Albinoburmese.com explains it pretty well and will save me alot of typing.
This post is by Craig,
I did not recommend feeding 20% BW. I recommend people feed growing Burmese pythons 10% of their body weight every 4-14 days (length of time depending on age/size/growthrate). A meal size of 20% would be considered an excess, and that sort of overfeeding will not be helpful to the animal. So, shoot for 10%. Did you happen to get your snake weighed when you saw the vet?
The nutrient breakdown of an adult rat is as follows:
(weight= 330 grams which would be considered large but not colossal)
% water = 66
% kcals from protein = 55
% kcals from fat = 43
% kcals from carbos = 2
mg/kcal calcium = 4.4
mg/kcal phosphorus = 3.2
as fed, the energy supplied to your snake from a rat will be aprox. 1.6kcal/gram.
therefore, a 330 gram rat contains about 528 kcals.
a 15,000 gram snake (about 33 pounds) that's still growing will need anywhere between 257 and 642 kcals/day*, or if you're feeding once a week, 1,799 to 4,494 kcal/week or about 3.5 to 9 adult 330g rats/week. (I've calculated this for 30C or 86F). The variations depend on many factors concerning snake growth and metabolism. For your snake that has been used to being underfed, I'd start with the standard metabolic rate (SMR), which is the lower number, and gradually increase to 1.5 SMR. For this to work well, we need acurate weight of the animals.
A rabbit (common domestic - Oryctolagus cuniculus) supplies much more water and a little less energy density. I calculated an as fed basis for a whole rabbit carcass (the following doc only lists dry matter basis) and found your average domestic rabbit is 0.76 kcals/gram. It therefore takes about half as many grams of rodents as it does rabbits to supply equal calories. However, it's easy to feed one 13 pound rabbit and more difficult to feed 9 rats (about 6.5 pounds) rats! For our mystical 33lb. snake, it would take anywhere between 5.3lb to 13 pounds of rabbits per week.
Here's the bottomline lowdown dirty summary:
For 1000 kilocalories, it takes a 625 gram (~1.375lb) of rat or a 1315 gram (~2.9lb.) rabbit. It's very difficult to find a 625g rat, but easy to find a 3lb. rabbit. There's also evidence that suggests GI health is stimulated by lesser biological foodstuffs like rabbits as opposed to rats.
I got much of this information from a USDA article which I'm now posting here and on my website. Click here to view the PDF about whole prey nutrient composition.
* This is from a reference in this book: Mader DR: Reptile Medicine and Surgery. W.B. Saunders Company, Philidelphia, 1996. p 150
Here is the link to the PDF refered to in the post. It is very informative.
http://www.albinoburmese.com/article...nal02May29.pdf
As you can see here I am not over feeding my burm. He weighs approx. 95lbs at 13ft. and will be 12 years old on the 4th of July. he is a very mature male and he does cruise the cage within about 8 days of having eaten a 8-10lb rabbit. I don't just feed him when ever he looks hungry, I have him on a strict schedule that is only interupted by his sheds, after which I usually give him a nice big rabbit since he is ravenous right after he sheds. I don't want a fat snake. Burms are heavy bodied by nature though. Unlike retics which have a leaner body. I hope this explains it all to you.
David
