I have three mouse eaters - one sub adult one juvie and one hatchling - they won't even look at a rat let alone kill and eat one. All three of them are as healthy as can be - however - they are all smaller than their siblings and other rat eaters thier age. Am I worried - no I think in the long run they will all catch up - these three are all lean muscular healthy animals and thats what counts.
As far as nutritional value goes the following link will give you all the information you need - but remember one thing - if your feeders are getting fed junk food - then they aren't going to be as healthy as the could be - make sure you buy your feeders from a good source!
Anyway - hope this helps!
Nutritional Values
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Tosha 
"One of these days i am going to wake up..look around...and realize my place looks more like "Ace Venturas"s than my own." Coldthumb
7.33.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Skywalker)
0.0.1 Green Tree Python
0.2.0 Feline (Pippen and Pandora)
0.0.1 Dessert Tortoise (Pope John Paul "JP"
2.2.1 Fish (1,2,3,4)
0.0.2 frogs rescued from pool skimmer
0.0.1 lizard rescued from vicious feline