Wool length and radiant heating effects in sheep

Abstract

1. When Merinos of varying wool lengths were exposed at constant air temperature of 36° C. (c. 97° F.) to infra-red radiation of energy equivalent to that which they might receive from the sun, the following responses were noted:(a) A very highly significant (P < 0·001) inverse relationship between respiration rate and wool length.(b) A non-significant inverse relationship between rectal temperature and wool length.(c) A very highly significant (P < 0·001) quadratic relationship between back wool-tip temperature and wool length.(d) A very highly significant (P < 0·001) inverse relationship between back-skin temperature and wool length.Thus, the length of wool determines to a large extent the degree of protection given to the sheep against radiant heat.2. The rate of conduction of heat per unit area through the back wool in different sheep was hyperbolically related to wool length. Below 1 cm. woollength heat was taken up very rapidly; beyond 4 cm., increasing wool length afforded negligible additional protection.