Gut microbes may influence host energy balance via a process called Urea Nitrogen Salvage (UNS). This microbial recycling has been proposed as a mechanism for nitrogen conservation in hibernators. The arctic ground squirrel is an exceptional hibernator, displaying the most extreme hibernation phenotype known: hibernation lasts up to nine months with no food or water consumption, and Tb during torpor is regulated at -2.9°C, the lowest of any mammal. That leaves the animal with just a short window of activity to complete the full reproductive cycle and prepare for the next hibernation. Earlier studies suggest that demands of hibernation might have enabled selection of the ureolytic microflora and increased relevance of UNS as a source of N. Here we tested whether high protein demands of gestation and lactation also increase incorporation of microbially-liberated urea-N into maternal tissues of active squirrels. Gestating and lactating animals were fed either a protein deficient or protein sufficient diet throughout the entire reproductive cycle. We measured microbial urea-N incorporation using isotopically labeled urea and assessed the bacterial diversity of gut microbiota. We found higher ureolytic bacteria activity and urea-N incorporation in the protein deficient group. Lactating squirrels on the protein deficient diet showed the highest incorporation of urea-N in their tissue and breath, signifying higher UNS.