| Popis: |
PIGS (33-66 days old) were exposed to ambient tem-peratures of 15, 20, 25, 30, 35 and 37.5 °C in 88 experiments. Data collected included hypothalamic, rectal and 8 skin surface temperatures, oxygen con-sumption, carbon dioxide production, respiratory evaporative water loss, respiration rate and regional skin surface areas. Pigs maintained homeothermy dur-ing cold stress by progressively increasing metabolic heat production (57 W/m2 at Ta = 30 °C to 123 W/m2 at Ta = 15 °C). Simultaneous increases in peripheral vasoconstriction during mild cold stress were implied by changes in calculated extremity tissue insulation from 0.06 °C-m2/W at Ta = 35 °C to 3.50 °C-m2/W at 25 °C. Thermal balance during heat stress was main-tained by increases in respiratory frequency (18 to 156/min.) and respiratory evaporative heat loss (10.4 to 24.8 W/m2). Peripheral vasodilation was maximal at 35 and 37.5 °C. Above Ta = 30 °C, pigs progressively elevated rectal and hypothalamic temperatures with an increasing difference between them. These data indicated a narrow range of thermoneutrality, overlap-ping vasomotor and metabolic responses to cold and overlapping respiratory and heat storage defenses during heat stress. |
