Meeting Abstract

39.3  Wednesday, Jan. 5  LIMITS ON BONE MOBILIZATION DURING REPRODUCTION HOOD, Wendy R; Auburn University wrhood@auburn.edu

In iteroparous species, future reproductive capacity is dependent on an individual’s ability to retain sufficient body condition during prior bouts of reproduction to support survival and capacity to reproduce again. Mammalian mothers mobilize mineral from their own bone to support development of their offspring’s skeletons and bone mobilization. Thus, bone fragility increases with increasing litter size, and mothers with large litters are expected to trade off risk of fracture with probably of survival to the next reproductive bout. The goal of this study was to determine if there is a physiological limit to the amount of bone that is mobilized during reproduction, a constraint that would act to protect the integrity of the maternal skeleton. Litter sizes of ICR lab mice were adjusted to 3, 8, 13 and 18 young on the day of parturition to characterize changes in maternal bone mineral content relative to offspring demand. Femoral and total body mineral content of mothers at weaning was examined relative to litter size. Total body fat was also examined to determine if energy stores follow comparable trends. The results of this study suggest that there are physiological limits to the amount of body fat and total body mineral that are mobilized to young during lactation with residual body fat and mineral decreasing to 13 pups and then plateauing for larger litters. However, femoral mineral appeared to hit a minimum for mothers supporting 13 young while females with 18 young had nearly 10% more femoral. Higher femoral mineral in females with the largest litters appears to be a benefit of cannibalism. Based on the relationship between femoral bone mineral content and number of days each pup in the litter was suckled, it appears that mothers benefit primarily from the savings incurred by suckling fewer offspring to weaning.