I probably keep mine more on the leaner side. Large or jumbo rats are usually sufficient - they don't need to eat as much as their size would suggest, since they generally aren't that active. My biggest red bloods (~6 ft) eat one every week or so. Occasionally I'll skip weeks, and occasionally they get extra because the balls weren't hungry. Bigger or more meals could be done before breeding though. My 4-5 footers eat about the same - they seem to need more for their size since they are still growing.