Abstract
Energy balance during lactation critically influences survival and growth of a mother's offspring, and hence, her reproductive success. Most experiments have investigated the influence of a single factor (e.g., ambient temperature [T(a)] or litter size) on the energetics of lactation. Here, we determined the impact of multiple interventions, including increased conductive heat loss consequent to dorsal fur removal, cold exposure (T(a) of 5 degrees C versus 23 degrees C), and differential lactational load from litters of different sizes (2 or 4 pups), on maternal energy balance and offspring development of Siberian hamsters (Phodopus sungorus). Lower T(a), fur removal, and larger litters were associated with increased maternal food consumption. Females exposed to multiple challenges (e.g., both fur loss and lower T(a)) ate substantially more food than those exposed to a single challenge, with no apparent ceiling to elevated food intake (increases up to 538%). Thus, energy intake of dams under these conditions does not appear to be limited by feeding behavior or the size of the digestive tract. Housing at 5 degrees C attenuated pup weight gain and increased pup mortality to more than 5 times that of litters housed at 23 degrees C. Increases in the dam's conductive heat loss induced by fur removal did not affect pup weight gain or survival, suggesting that effects of low T(a) on pup weight gain and survival reflect limitations in the pups' ability to ingest or incorporate energy.