EFFECTS OF COLD ENVIRONMENTS ON THE ENERGY EXCHANGES OF YOUNG BEEF CATTLE

Groups of four heifers were kept over winter at 20 C (controls) or outdoors with (sheltered) or without (exposed) shelter. Weather conditions were severe. Mean January temperature was −28 C. All animals received the same amount of grain. Calves in the control, sheltered and exposed groups ate on average 9.0, 11.3 and 10.9 g hay/kg body weight per day and gained, over winter, 156, 158 and 140 kg, respectively. Growth of new hair was similar in all groups. However, total hair cover in the cattle kept outside was, in February, twice that of the controls. This increase was attributed to reduced hair shedding. Tissue insulation increased throughout in all groups. External insulation was markedly reduced by exposure of the animals to wind. The influence of coat depth on external insulation was small. Still air critical temperature for the controls fell from 7 to −2 C during the experiment. The effect of acclimatization was to reduce critical temperature to −18 C in the sheltered group during February.The results are discussed with respect to the nature and extent of environmental control required for beef production in cold climates.