Abstract

Milk is the sole food source of mammals during early postnatal development, and its composition may be modified to meet changing nutritional and energetic demands from birth to weaning. These demands are especially acute in small mammals that breed in highly seasonal environments. We investigated the temporal course of milk composition during lactation in free-living yellow-pine chipmunks, Tamias amoenus, a small altricial omnivorous rodent that produces a single annual litter immediately after emerging from hibernation. Over the course of lactation the total energy concentration of milk increased more than two-fold, to approximately 13 kJ ml-1. The main component of the milk was lipids, which increased from 10 to 30% of total milk content by wet mass. Proteins increased from approximately 5 to 10%, whereas carbohydrates remained low, at 4-5%. The progressive augmentation of milk energy content during lactation contributes to the increased demands of rapid growth in this altricial species. © 2002 Elsevier Science Inc. All rights reserved.