NUTRITIONAL-REQUIREMENTS FOR REPRODUCTION IN THE HISPID COTTON RAT, SIGMODON HISPIDUS

To better understand resource allocation in the herbivore Sigmodon his pidus, nutritional requirements for reproduction were determined. Adul t female cotton rats were fed Purina (R) #5001 Laboratory Chow ad lib in the laboratory. They and their progeny were sacrificed at either 10 , 20, 24, or 26 days after breeding, at birth (27 days), or at weaning (39 days). Protein, lipid, and element concentrations in body tissues of pregnant females were constant. From birth to weaning, protein con centration in lactating females increased and lipid concentration decr eased, whereas no concentration of elements changed significantly. In progeny, concentration of protein, K, Na, Fe, Zn, and Cu declined sign ificantly, while concentration of lipids, Ca, P, Mg, Mn, and energy in creased significantly from birth to weaning. An energy and mass-balanc e analysis indicated that laboratory chow easily met nutritional requi rements for reproduction. This analysis was used to estimate minimum n utritional requirements for reproduction in S. hispidus. A second ener gy and mass-balance analysis using a natural diet indicated that prote in and phosphorus ingestion by adult females was lower during autumn a nd winter than required for production of a litter. Thus, protein and phosphorus are critical dietary components that may limit reproduction in S. hispidus under field conditions.