DIGESTIBILITY AND ASSIMILATION OF NATURAL FORAGES BY MUSKRAT

Knowledge of the forage intake and digestive efficiencies of muskrat ( Ondatra zibethicus) is essential for developing an understanding of th eir habitat requirements and their impact on emergent vegetation. We p erformed 30 complete digestibility, energy-, and nitrogen-balance tria ls on 6 adult male muskrat fed 5 diets: (1) sedge (Carex atherodes) sh oot, (2) softstem bulrush (Scirpus validus) shoot, (3) hybrid cattail (Typha x glauca) shoot, (4) cattail rhizome, and (5) a combination of cattail shoot and rhizome. Dry matter (DM) digestibilities ranged from 61.2 to 70.6%. Neutral detergent fiber (NDF) digestibilities varied f rom 40.0 to 59.6% for these emergent plant diets with NDF levels rangi ng from 44.6 to 62.1%. Microbial fermentation of fiber accounted for 3 9.4% of digestible energy (DE) intake. Muskrat can digest fiber as wel l as can many ruminants and pseudoruminants, but can do so more effici ently than other rodents. Apparent digestibility of dietary crude prot ein (DCP) was highest (P < 0.001) for sedge (73.6%) and lowest (P = 0. 001) for the cattail rhizome diet (7.2%). However, the daily nitrogen intake (DNI) required by muskrat to maintain tissue balance on a catta il rhizome diet (0.599 g N/kg0.75/day) was less than half the daily in take required for all other diets combined (1.266 g N/kg0.75/day) (P < 0.001). This implies the existence of a protein conservation mechanis m by which muskrat could negate the effects of low dietary crude prote in during winter.