SEASONAL ENERGY EXPENDITURES AND THERMOREGULATORY RESPONSES OF BISON AND CATTLE

Abstract

The metabolic rates of two bison and four Hereford spring-born calves were measured at monthly intervals from December until the following November. Following adaptation at seasonal ambient temperatures, metabolic measurements were made while calves were exposed to controlled temperatures of +10, 0 and −30 °C. Exposure of the Hereford calves to −30 °C resulted in increased metabolic rates during the first 6 mo of the study but the magnitude of the response was greatly attenuated as the calves grew larger. At −30 °C, bison calves either maintained or reduced metabolic rates compared to expenditures at +10 °C. When the calves were about 17 mo of age, they were exposed to a combination of low temperatures and wind. Wind velocities of 4.7 km∙h−1 did not influence metabolic rates of either bison or Herefords at air temperatures of 0 °C. However, at −30 °C, metabolic rates increased from 650 and 700 KJ∙kg−.75∙d−1 to 835 and 950 KJ∙kg−.75∙d−1 in Hereford and bison calves, respectively. Neither respiratory frequencies nor heart rates were influenced significantly during cold exposure, but heart rates increased in response to wind. In general, metabolic rates and heart rates were lower in bison calves.