The absorptivity for solar radiation of different coloured hairy coats of cattle

Abstract

1. The mean effective absorptivity for solar radiation of the hairy coats of cattle was determined. It was found that the colour of the hair is the most important characteristic in effecting the total percentage of radiation absorbed. 2. The mean effective absorptivity was found to be 49 per cent. for the hairy coat of a white Zulu, 78 per cent. for that of a red Afrikaner and 89 per cent. for that of a black Aberdeen Angus. 3. The difference in absorption due to the direction of the hair in relation to the direction of the incoming solar beam was found to be not more than 4 per cent. (usually 1 to 2 per cent.). 4. No appreciable difference was found between the absorptivity of an autumn and a winter coat of two Afrikaner beasts. The mean absorptivity of a Sussex winter coat was not more than 2 per cent. higher than that of a Sussex summer coat. 5. A comparison of the absorptivity of an Afrikaner autumn coat with the hair smoothed down and with the hair standing up showed no appreciable difference. 6. After clipping a long-haired Sussex winter coat to about ½ inch in length, the mean effective absorptivity was found to be 2 per cent. lower than on the unclipped curly hair. This smaller absorption was probably due to the slightly lighter colour of the clipped hair. 7. The comparison of six hairy coats of different shades of red and of different grades of smoothness showed that the mean effective absorptivity varied between 78 per cent. and 83 per cent. The above findings show that the colour is the most important factor effecting the absorptivity of hairy coats for solar radiation, and that direction of the hair, its smoothness or curliness and seasonal changes in the character of the coat are of secondary importance.