Knowledge of the forage intake and digestive efficiencies of muskrat (Ondatra zibethicus) is essential for developing an understanding of their habitat requirements and their impact on emergent vegetation. We performed 30 complete digestibility, energy-, and nitrogen-balance trials on 6 adult male muskrat fed 5 diets: (1) sedge (Carex atherodes) shoot, (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 from 40.0 to 59.6% for these emergent plant diets with NDF levels ranging from 44.6 to 62.1%. Microbial fermentation of fiber accounted for 39.4% of digestible energy (DE) intake. Muskrat can digest fiber as well as can many ruminants and pseudoruminants, but can do so more efficiently than other rodents. Apparent digestibility of dietary crude protein (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 cattail rhizome diet (0.599 g N/kg super(0.75)/day) was less than half the daily intake required for all other diets combined (1.266 g N/kg super(0.75)/day) (P < 0.001). This implies the existence of a protein conservation mechanism by which muskrat could negate the effects of low dietary crude protein during winter.
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