Seasonal changes in heat balance of dogs acclimatized to outdoor climate.

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Abstract
Heat production (M), dry heat loss (R + C), evaporative heat loss (E) and rectal temperature (Tre) were measured in a direct calorimeter in female mongrel dogs acclimatized to outdoor climate at Kanazawa (latitude, 36.degree.35"N) Japan. M and total dry and evaporative heat losses (HL) were minimal at calorimeter wall temperatures (Tw) of 26-29.degree. C in summer and 22-26.degree. C in winter (thermoneutral temperature, TNT). The seasonal shift of the lower critical temperature was confirmed. At Tw below TNT, the values of M and HL were significantly higher in summer. At Tw above TNT, these values increased. At TNT and above, M and HL were significantly higher in winter. (R + C) decreased linearly with increasing Tw in both seasons. At Tw below 26.degree. C, (R + C) were significantly higher in summer. At Tw above 26.degree. C, E increased greatly. The values of E were significantly higher in winter at Tw 29-32.degree. C. Tre remained nearly constant at TNT and below, and increased at above TNT in both seasons. Mean body surface temperature (.hivin.Tsf) decreased with decreasing Tw. Body thermal conductance (K) was minimum at Tw below 26.degree. C in summer and at Tw below 22.degree. C in winter. At Tw above these temperatures, K increased significantly. Whole body insulation (I) was significantly higher in winter, particularly at Tw 18.degree. C. The dogs reared outdoors in winter apparently acclimatized to cold in 2 ways; by increasing the insulating effect of the fur coat and by elevating resting heat production.

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