- We partitioned the metabolizable energy intake (MEI) into energy for maintenance (ME m) and for growth (ME g) in sucking precocial and altricial rodent pups. Each of the two components includes energy loss due to the heat increment of feeding. ME m of precocial pups expressed as average daily energy costs or as a proportion of MEI was greater than in altricial pups of similar size and, therefore, less energy was available for growth. Consequently, the overall energy cost (via total MEI) per unit postnatal growth of precocial pups was greater than for altricial pups of similar size. We used the proportion of calculated ME m to that predicted by body mass as an index of precociality in rodent pups. The proportion of ME g to MEI in precocial pups was lower than in altricial pups and was inversely related to the index of precociality.