The Sweat Gland Response To Solar Radiation In Three Species Of Domestic Animals

Abstract

The present understanding of evaporative heat loss mechanisms in domestic farm animals. is based on data gathered from experiments, carried out in animals exposed to simulated desert conditions in climatic chambers. Relatively few experiments have been carried out in the field, when animals are exposed to the full natural environmental solar and heat loads. The quantitative effects of ambient temperature and solar radiation on sweating rate, body and skin temperatures were studied in three species of domestic farm animals: Somali donkey (Eguus asinus), East African goat (Capra hircus), and indigenous breeds of cattle, (Bos indicus). Cutaneous moisture evaporation, skin and body temperatures were observed in the field employing a partial shade technique which involved shading one half of the animal and leaving the other side exposed to natural environmental solar and heat loads. Sweat rates and skin temperature on the heated and shaded sides of the animals were compared, using the Van't Hoff's rule and mean Q.lO values between 205 and 3~5 were obtained. similarly, 2 insensible. water loss 1;(10 values were between 1.2 and 103. In experiments carried out in the climatic chamber localized sweating was monitored in response to a thermal stimulus. From a continuous recording of cutaneous moisture vaporization (CMY) increases and decreases in local skin temperature were observed with corresponding changes in cutaneous moisture vaporizationo Differences in field and laboratory values for CMY were noted. In cattle, for example, CMY values of 200 g H20/m2• hr. were obtained in the laboratory compared with field values of 35~ g H20/m20 hr. These differences can be explained on the basis of a simple CMY QIO effect " The higher CMY values obtained in the field experiments emphasized the importance of solar radiation in promoting sweating by acting on the temperature sensitive sweat gland neuro-effector junction.