PARSONS, J.L.*; HELLGREN, E.C.; LOCHMILLER, R.L. (deceased); LESLIE, D.M., JR.; JORGENSEN, E.E.: Protein nutrition of Southern Plains small mammals: Comparative nitrogen requirements for reproduction

Nitrogen nutrition and dynamics in animal communities are of increasing interest, given growing amounts of nitrogen in terrestrial and aquatic systems and the role of nitrogen as an essential nutrient. We performed feeding trials on two small mammal species (the hispid cotton rat, Sigmodon hispidus, and the fulvous harvest mouse, Reithrodontomys fulvescens) to determine nitrogen requirements for reproduction. Because of the relatively low-protein diet of wild cotton rats, we predicted that S. hispidus would have a lower nitrogen requirement than R. fulvescens. Females were fed one of seven experimental diets (1% to 3.5% nitrogen) from the third trimester ofgestation through lactation. Offspring were weighed every other day from birth until weaning, and pup growth rate was regressed on maternal nitrogen intake. A breakpoint analysis was performed to determine each species’ reproductive requirement. Our data indicate that S. hispidus required 2.47% dietary nitrogen (2731.08 mg/kg^0.75) and R. fulvescens required 1.69% nitrogen (2258.48 mg/kg^0.75) for maximal reproduction. Although our prediction was not upheld, the use of maximum reproductive output to define nitrogen requirements may not reflect the reality of free-ranging animals. Results will be discussed with regard to interspecies comparisons, dietary niche and life-history strategies, and alternate analyses will be proposed to find a more ecologically relevant definition of reproductive requirements.