>You won't stop your snake from growing long by feeding it less. >However, you can reduce the chance of obesity by not >overfeeding.
Maybe I am not understanding this right? But if you feed a young snake less, I believe it will cut back on it's overall length. But this applies to the earlier years, mainly 1-3 I would presume.
Also, Tim pointed out the competition of a pinky rat being fattier than a mouse of the same size. I would guess less calcium too? I'll read that info on rodent pro in a sec.
A few post say things in generalities. "Rats have the same nutrition as a mouse". I'd say yes, at the same age of a mouse and rat. But I sell a lot of feed. And most people switching to a rat, want a rat the size or just a little larger than a mouse. That's a rat pup, not a fully developed rat.
I totally agree with Tim, it will put on weight, but if the snake will never grow large enough to get off rat pups (2-3 weeks old) I would lean to the idea it would just use all that fat to become overweight, much like me! 
So, when I have a person that wants to switch to rats, I want to find out if it will be big enough to take a 6-7 week old rats. I feel by that age the rats are more lean and similar to a mouse.
IMHOOC
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Thanks for reading.
Big Tom
www.HerpZillA.com