Effect of clipping and of shading calves on cutaneous evaporation.

Abstract

EFFECT OF CLIPPING AND OF SHADING CALVES ON CUTANEOUS EVAPORATION D. M. MURRAY ' Summary Two calves, one a pure Hereford and the other a Hereford x Santa Gertrudis crossbred, have been exposed to moderate heat stress in the field and the effect on cutaneous evaporation of (i) clipping and (ii) shading the animals from direct solar radiation, investigated. The cutaneous evaporation rate from the shoulder area of the Hereford calf was unaffected by clipping while that of the crossbred calf showed a 14% increase. Shading the two calves for 2 hours at mid-day caused a 60% reduction in the cutaneous evaporation rates of both animals. Associated changes in rectal temperature, respiratory rate and skin temperature during clipping and shading observations are also reported. I. INTRODUCTION Psychrometric studies by Yeates (1955) using Shorthorns, and Bianca (1959) using Ayrshires suggest, indirectly, that a woolly coat may interfere with evaporation of sweat. In these studies, clipping woolly-coated animals caused a fall in rectal temperature and respiratory rate, which could not be attributed to increased non-evaporative heat loss, since both experiments were conducted at 40-40.5'C (104-105�F). In a field experiment, however, Turner (1962) measured cutaneous evaporation from small clipped patches on unclipped and clipped Hereford calves and found no change in evaporative moisture loss associated with clipping. The present study was designed to investigate the possibility of a short-term alteration in cutaneous evaporation following (a) clipping, and (b) shading the whole body surface, using Hereford and Hereford x Santa Gertrudis calves. II. METHODS To determine the possible significance of coat cover on moisture loss from the skin, the cutaneous evaporation rates of two calves were measured before and again two days after clipping, using the ventilated capsule technique (Taneja 1959). One of the calves was a purebred Hereford which had a long, wooll y coat; the other, a % Hereford-l! Santa Gertrudis which possessed a flat, sleek coat. Coat lengths were 3.0 and 2.5 cm respectively. Rectal temperatures were measured with a clinical thermometer, respiratory rates by counting flank movements and skin temperatures using a copper-constantan thermocouple inserted into the capsule. These observations were animals were exposed to direct tures were similar on both days movement varied slightly from made between 10 a.m. and 3 p.m. while the solar radiation in December. Dry-bulb temperabeing in the vicinity of 27�C (SOOF), while air 100 to 125 cm/set (200 to 250 ft/min). +:Department of Livestock Husbandry, University of New England, Armidale, N.S.W. 424 TABLE 1 Eflect of clipping on rectal temperature, respiratory rate, cutaneous evaporation and skin temperature *Each value represents the mean of 4 approximately hourly readings. t S.E. Sg/mVhr from a standard area on the shoulder. In the shading experiment, the two calves were protected from direct solar radiation for two hours about midday. This was achieved by erecting a 1.7 x 1 m light plywood frame 0.5 m above the back of each animal. III. RESULTS AND DIXUSSION The effects of clipping on the physiological indices measured are shown in Table 1. Although the cutaneous evaporation rate of the Hereford calf was unaffected by clipping, rectal and skin temperature decreased presumably as a result of increased non-evaporative heat loss. On the other hand, clipping the more heat tolerant crossbred calf caused a 14% increase in evaporation from the skin, . while skin temperature decreased. The slight increases in rectal temperature (39.1 O v. 39.4'C at 1 p.m.) and respiratory rate of the clipped crossbred calf suggest that the increased evaporation was the result of increased skin sensitivity rather than simple facilitation of evaporation. The different responses of cutaneous evaporation to clipping in the two calves may reflect genetic differences in the sensitivity of sweat glands to respond to a change in their environment. As the sweat glands of Bos indicus cross animals are located nearer the skin surface than in British breeds (Dowling 1955), they may respond to external stimuli more readily. This explanation receives support from the finding of Walker (1957), who reported that the heat tolerance of several breeds of indigenous African cattle varied inversely with the thickness of the papillary layer of the skin. The effect of shading on cutaneous evaporation in the clipped calves is illustrated in Figure 1. During shading, evaporation from the skin of both animals decreased markedly, which was followed by a rapid increase in cutaneous evaporation after removal of the shades. Respiratory rates followed a similar pattern to cutaneous evaporation with the Hereford showing the greater fall in respiratory activity during shading and increase after the shades had been removed. Rectal temperatures showed little change during shading but increased after the shades were removed, the increase again being greater in the Hereford. Skin temperatures and cutaneous evaporation during shading were found to vary independently, 425 Fig. l.-Cutaneous evaporation (-) and skin temperature ( - - - ) responses of the Hereford crossbred ( l ) and Hereford (0) calves before, during and after shading. The block indicates the time and duration of shading. suggesting that the action of direct solar radiation on sweat glands could be a direct one, rather than indirect stimulation mediated by an elevation of skin temperature. IV. ACKNOWLEDGMENTS The author wishes to acknowledge Mr. M. K. Hill, Department of Livestock Husbandry, University of New England, for invaluable criticism and discussion. V. REFERENCES , W. (1959). The effect of clipping the coat on various reactions of calves to heat. Journal of Agricultural Science 52: 380. DOWLING, D. F. (1955). The thickness of cattle skin. Australian Journal of Agricultural Research 6: 776. T ANEJA , G. C. (1959). Sweating in cattle. II. Cutaneous evaporative loss measured from limited areas and its relationship with skin, rectal and air temperature. Journal of Agricultural Science 52: 50. T URNER , H. G. (1962). Effect of clipping the coat on performance of calves in the field. Australian Journal of Agricultural Research 13: 180. W ALKER , C. A. (1957). The skin thickness of cattle in Northern Rhodesia. Journal of Agricultural Science 49: 211. Y EATES , N. T. M. (1955). Photoperiodicity in cattle. I. Seasonal changes in coat character and their importance in heat regulation. Australian Journal of Agricultural Research 6: B IANCA 891. 426