>>2) give him rats instead of mices (it's more nutritive)
Still under debate. That last report I saw has them at about even when you break down total nutrition by each factor (protien, carbs, fat, etc.).
>>3) several preys total amount 1/3 of his weight
I don't go by weight. Generally, my snakes eat what they want. They let me know when full. They are not obese and most go off-feed at least 4 months of the year. These fat reserves carry them through this period.
>>4) as soon as he defece you feed him again
If you wait until they defecate, you could have one skinny snake. I have snakes that will eat 8-10 med/large rats in between fecal cycles - that's 8-10 rats a month.
Obesity is difficult to determine in Ball Pythons. By their very nature, they are large-bodied snakes. So, what determines, without opening up the snake, that it's obese? Some extreme cases it might be easy. With the average Ball Python, I don't think it's possible. I await a study in this area.
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Jay A. Martin