Digestibility, nitrogen excretion, and mean retention time by North American porcupines (Erethizon dorsatum) consuming natural forages

North American porcupines (Erethizon dorsatum) subsist predominantly on low -protein, high-fiber, high-tannin diets. Therefore, we measured the porcupi ne's ability to digest dry matter, fiber, and protein by conducting digesti on trials on eight natural forages and one pelleted ration varying in conce ntration of fiber, nitrogen, and tannins. On these diets, dry matter intake ranged from 5 to 234 g/kg(0.75)/d and dry matter digestibility ranged from 62% to 96%. Porcupines digested highly lignified fiber better than many la rge hindgut fermenters and ruminants. The porcupine's ability to digest fib er may be explained, in part, by their lengthy mean retention time of parti cles (38.43 +/- 0.56 h). True nitrogen digestibility was 92% for non-tannin forages and pellets. Endogenous urinary nitrogen was 205 mg N/kg(0.75)/d, and metabolic fecal nitrogen was 2.8 g N/kg dry matter intake. Porcupines a chieved nitrogen balance at relatively low levels of nitrogen intake (346 m g N/kg(0.75)/d). Tannins reduced the porcupines' ability to digest protein. However, the reduction in protein digestion was not predictable from the a mount of bovine serum albumin precipitated. Like many herbivores, porcupine s may ameliorate the effects of certain tannins in natural forages on prote in digestibility through physiological and behavioral adaptations.