PARSONS, J.L.*; HELLGREN, E.C.; PRUETT, P.; ROSAS, C.; LESLIE, D.M., JR.; JORGENSEN, E.E.; Oklahoma Cooperative Fish and Wildlife Research Unit, Stillwater; Oklahoma State University, Stillwater; Oklahoma State University, Stillwater; Oklahoma State University, Stillwater; Oklahoma Cooperative Fish and Wildlife Research Unit, Stillwater; USEPA, Ada, Oklahoma; ; : Comparative digestibility of dry matter, nitrogen and fiber in Southern Plains small mammals

Animals adapted to distinct dietary niches often have differing digestive capacities, due to differences in gut length or mass, digestive enzyme activity, or microbial fermentation. We compared dry matter, N, and fiber digestibility in 3 sympatric species (hispid cotton rat [Sigmodon hispidus,], white footed mouse [Peromyscus leucopus], and fulvous harvest mouse [Reithrodontomys fulvescens,]) that represent different dietary niches. Based on free-ranging diet, we predicted that S. hispidus would show the highest digestive efficiencies, followed by R. fulvescens and P. leucopus. We fed animals one of 7 experimental diets (1-3.5% N), determined dry matter and N intake and fecal excretion, and compared dry matter, apparent N, and true N digestibilities through regression and ANOVA. We also fed cotton rats and harvest mice high- and low-fiber rations, compared fiber digestibility with repeated-measures ANOVA, and examined gut morphology. We found that S. hispidus had the highest digestive efficiencies in all cases and R. fulvescens had the lowest, but there were no differences in organ dimensions. Although our prediction was not entirely upheld, the smaller body size of harvest mice may have dictated higher mass-specific metabolic rates and higher intake and passage rates. The diet of Peromyscus spp. also contains high proportions of indigestible chitin; thus, higher retention times and more thorough digestion would follow. Observed differences in digestibility may be attributed to shifts in digestive function rather than gross morphology.