Seasonal energetic parameters of free-grazing bison (Bison bison)

Seasonal energetic parameters of yearling bison were estimated using the bi te-count and single marker methods (field trials) during each solstice and equinox between June 1994 and December 1995. To calibrate the marker method and to provide a controlled estimate of seasonal requirements, balance tri als were conducted in metabolism crates during winter solstice 1993 and sum mer solstice 1995 (pen trials). In pen trials, actual metabolizable energy (ME) intake was lower (P < 0.01) during winter (528 +/- 51 kJ W-0.75 d(-1)) than in summer (917 +/- 69 kJ W-0.75 d(-1)). Similarly, in field trials, e stimated ME intakes were lower for both bite count (P < 0.01) and marker me thods (P < 0.05) during winter (819 +/- 375, 146 +/- 105 kJ W-0.75 d(-1)) t han summer (1977 +/- 186, 408 +/- 53 kJ W-0.75 d(-1)), respectively. Estima ted ME requirements tactual intake, pen trials) were 532 +/- 178 kJ W-0.75 d(-1) in winter and 956 +/- 107 kJ W-0.75 d(-1) in summer. In field trials, estimated ME requirements (marker method) ranged from 146 +/- 22 kJ W-0.75 d(-1) (December 1994) to 478 +/- 45 kJ W-0.75 d(-1) (June 1995). Seasonal variation (P < 0.05) in total digesta turnover time (46.4 +/- 1.4 h, Decemb er 1994; 24.9 +/- 2.7 h, June 1995) was related more consistently to season al differences in transit time (18.2 +/- 1.2 h, 4.0 +/- 0.8 h, respectively ) than differences in reticulo-rumen and lower tract turnover time. Bison e xhibited strong seasonal differences in energetic parameters like other nor thern wild ruminants.