P3.79 Thursday, Jan. 6 Temporal and inter-individual variation in milk composition in a free-ranging, hibernating rodent SKIBIEL, Amy/L*; HOOD, Wendy/R; Auburn University; Auburn University email@example.com
A female's ability to maintain the appropriate concentration of nutrients in milk is essential for maximizing offspring growth and development. For hibernating mammals this need may be exacerbated by time constraints young face in ingesting sufficient resources post-weaning to survive hibernation. Maternal investment promoting faster growth of young is expected to be selectively advantageous. Thus, milk containing a high concentration of protein, supporting rapid muscular development, and high energy lipids may be expected. The purpose of this study was to characterize temporal changes and examine inter-individual differences in milk composition in a hibernator, the Columbian ground squirrel. In addition, the relationships between milk composition and offspring growth rate (mass gained/d) and mass at weaning are examined. At peak lactation, the proximate composition of milk was 31.6% dry matter, 11.1% fat, and 3.7% carbohydrate. Mineral composition was 0.43% Ca, 0.36% P, 0.02% Mg, 0.16% K, and 0.09% Na. Carbohydrates, Ca, Mg, and P concentration increased throughout lactation and individual females differed with respect to the concentration of Mg, K, and fat in the milk, but not any other minerals, carbohydrates, or dry matter. The concentration of milk constituents at peak lactation did not affect offspring weaning mass and only the dry matter content of milk had a significant effect on the average growth rate of young during lactation. Overall, this study provides the first preliminary information about an important aspect of the Columbian ground squirrel's lactation strategy. The next phase of this research is to determine if variation among females in milk composition gives rise to patterns of variation in offspring survival.