Pelage insulation, litter size, and ambient temperature impact maternal energy intake and offspring development during lactation

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°C versus 23°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°C attenuated pup weight gain and increased pup mortality to more than 5 times that of litters housed at 23°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.