Modeling energy and protein reserves in support of gestation and lactation: glucose as a limiting metabolite in caribou and reindeer

Introduction In the CARMA (CircumArctic Rangifer Monitoring and Assessment) network we account for factors that a"ect reproduction and growth of an individual caribou through an energy/ protein model, which simulates body weight and condition of an individual female caribou (Rangifer tarandus) over time (Russell et al., 2005; Gunn et al., 2013; White et al., 2013). However, modeling mobilization of maternal fat and protein to support fetal growth and lactation is complex because energy and protein transactions occur through intermediary substrates (e.g., fatty acids, glucose, amino acids). In the energy/protein model, however, we do not overtly deal with intermediary substrates; rather, we model the amount of body fat and protein that can be measured in the #eld. CARMA has a large body condition data set for Arctic caribou (Rangifer tarandus) populations that allow us to set limits on seasonal fat and protein mobilization and accretion rates. Within the model we estimate daily energy and protein balances, and if negative, we estimate the amount of fat and protein that needs to be mobilized to satisfy demands. During gestation this exercise controls fetal growth, and during lactation it controls milk production and calf growth. As validation we rely on seasonal changes in body composition of female caribou (R. t. granti) of the Porcupine caribou herd (PCH) (Gerhart et al., 1996) and experimental data derived from caribou and reindeer (R. t. tarandus) fed a known diet and intake during late gestation (Barboza & Parker, 2006; 2008).