Tropical adaption of cattle : experimental inquiry into the effects of high air temperature on pregnancy and on cutaneous water loss

Abstract

The experiments described in this thesis were carried out in two parts. Part one deals with the effects of high air temperature on pregnancy in cows. For this study, twelve Brucellosis-free Australian Illawarra Shorthorn cows were divided into four groups of three each. One group acted as a control. Animals in each of the other three groups were heated at about the 10th, 30th and 50th day of pregnancy for 7-8 days at an average air temperature of 105oF dry-bulb and 88oF wet-bulb.In all but one, pregnancy proceeded normally and the birth weights of the caires of heated and of control cows were nearly the same. In one experimental animal heated at 30 day stage of pregnancy, subsequently returned to oestrus indicating that its original pregnancy failed. In the main, however, the heating conditions employed in these experiments had little effect and it must be concluded that the Australian Illawarra Shorthorn cows are relatively better adapted to tropical climate. The second part of the thesis deals with experiments on the effects of high air temperature on cutaneous evaporation in cattle. Five calves of four different breeds were used (one Zebu-Australian Illawarra Shorthorn crossbred, two Shorthorns, one American Brahman, and one Aberdeen Angus). A capsule method was developed to collect small quantities of moisture passing through the skin, without markedly altering the environmental conditions of the area under examination.Sweat glands ef eattie were found to be functional and their innervation adrenergic. Cattle use sweat to prevent body temperature from rising, yet the amount of sweat secreted is not large enough to allow cattle to maintain thermoneutrality at high air temperatures.With the microscope, sweat droplets may be observed at the openings of sweat ducts. These droplets may be detected by sweat prints on tannic acid papers applied to closely shaved skin areas smeared with ferric chloride solution. Skin washings of cattle exposed to heat contain only small traces of chloride that can be attributed to extraneous sources. It is probable that cattle sweat glands do not secrete chloride. .......