Okay I did a statistics project on feeding mice vs rats to baby balls for their first 16 meals. Gram for gram there was no statistically significant difference in growth rates between animals fed mice vs animals fed rats. However the animals we did not use in the study where significantly larger than those used in the study because we fed them rat pups from the get go. Ave rat pup size is 14-24g while ave small mouse is less than 10g normally 6-8g. So the rat eating animals in the study had to eat rat pinks and fuzzys because of the gram weight difference. So basically the more grams your animals eats the more it will grow period. It doesn't matter if it's rats or mice. Rats however are larger and given a single prey item it will provide way more food to the snake than any single mouse will. Weigh your mice see how much you are actually feeding them and know that small rats range from 50-70g.