SEASONAL CHANGE SIN METABOLIC RATES OF MUSKOXEN STANDARDIZED TO INTAKE FOLLOWING A TWENTY FOUR-HOUR FAST

James P. Lawler and Robert G. White
Institute of Arctic Biology, University of Alaska Fairbanks, AK 99774-7000, USA.

Resting metabolic rate was measured in three 3-year old muskoxen at 10 periods over the course of a year. Muskoxen were taken from pasture and fed a single standardized meal of 50% chopped hay and 50% pellets (Quality Texture) at 10g/kg BW^0.75. Then they were fasted 26 h, the final 2 h in an open circuit metabolic chamber monitoring oxygen, carbon dioxide, and methane exchange. Metabolic rates were lowest in April 1994 at 454 + 14.6 kJ/kg BW^0.75·d (1.09 + 0.03 W/kg) and highest in June 1995 at 454 + 14.6 kJ/kg BW^0.75·d (1.43 + 0.05 W/kg). The 31% seasonal extremes were significant (p=0.002) but less divergent than those reported by Nilssen et al. (1994: Rangifer 14:70-81) who found winter and summer metabolic rates of 0.86 ± 0.10 W/kg and 1.74 + 0.27 W/kg respectively after a 7-10 h fast. Methane production was 20 + 2.8 kJ/kg BW·d in June (p=0.005). These losses represent 6% and 3% of the total energy expenditure (metabolic rate + methane production) during April and June respectively. Seasonal shifts in metabolic rates from winter to summer were noted between April and May and the reverse occurred between August and September.