Sweating of the scrotal skin of Merino rams selected for high and low levels of skin fold.

Abstract

SWEATING OF THE SCROTAL SKIN OF MERINO RAMS SELECTED FOR HIGH AND LOW LEVELS OF SKIN FOLD D. G. FOWLER* Summary Merino rams selected for a high level of skin fold (Folds Plus) had lower scrotal skin sweat losses, higher subcutaneous scrotal temperatures and a greater scrotal surface area than rams selected for a low level of skin fold (Folds Minus). I. INTRODUCTION Waites and Moule ( 1961) observed a close relationship between subcutaneous scrotal temperature and intra-testicular temperature for Merino rams. In a later paper (Moule and Waites 1963)) they also found that rises in subcutaneous scrotal temperatures were accompanied by temporary infertility and suggested that the degree of seminal degeneration was likely to vary with factors affecting scrotal skin sweat loss. Fowler and Dun ( 1966) found that rams with a high level of skin folding (Folds Plus) had a greater susceptibility to heat induced infertility than rams with little skin folding (Folds Minus). The observations presented in this paper were undertaken to determine whether difference in sweat loss from the scrotal skin might be implicated in this difference in susceptibility to heat induced infertility. II. MATERIALS AND METHODS The fold selection flocks have been described by Dun (1964). Five of the most wrinkly Folds Plus and five of the least wrinkly Folds Minus rams aged three to four years were used in this experiment. The scrotal skin of each ram was heated in a chamber on two separate occasions. On the first occasion air temperature in the chamber was kept at 20�C for 90 minutes and then elevated to 37.8OC for 240 minutes. On the second occasion air temperature in the chamber was again maintained at 20�C for 90 minutes and then elevated to 42S'C for 240 minutes. The heating system, sweat collection apparatus and method for the determination of sweat gland discharge frequency were similar to that described by Waites and Voglmayr ( 1963). Subcutaneous scrotal temperature was measured once each minute with a thermocouple (Moule and Waites 1963). The surface area of the scrotal skin of each ram was measured from a flexible, inelastic cast of the scrotum. * Department of Agriculture, Agricultural Research Station, Trangie, N.S.W. 123 Fig. 1 .-Sweat loss (g) from the scrotal skin of Folds Plus and Folds Minus rams. III. RESULTS At each temperature the mean sweat loss from the scrotal skin in the Folds Minus rams was 60 to 70% higher than in the Folds Plus rams (Figure 1) . The difference approaches, but does not attain, statistical significance (P < 0.10). On the other hand the surface area of the scrotum in the Folds Plus rams (644 sq . cm . ) was greater (P <O.OS) than in the Folds Minus rams (540 sq. 124 TABLE 1 Scrotal sweat loss and subcutaneous scrotal temperature of Folds Plus and Folds Minus rams cm.), so that the difference between the two groups in sweat loss per unit area was greater than the total loss and it was significant statistically (P <0.05) (Table 1). In association with the greater sweat loss, the mean frequency of discharge of the sweat glands in the Folds Minus rams (3.4/hr) was greater (P <0.05) than that in the Folds Plus rams (2.7/hr) and the mean subcutaneous scrotal temperature was less (P <O.OS). IV. DISCUSSION A likely explanation for the greater susceptibility of Folds Plus rams to heat induced infertility appears to be a lower sweat loss and hence heat dissipating ability of the scrotal skin. Part of this difference in sweat loss may be due to a 26% higher sweat gland discharge rate for Folds Minus rams, but these rams also had a 16% lower scrotal surface area than Folds Plus rams. The density and size of scrotal sweat glands are associated with the amount of sweat loss (White and Caughley 1936; Waites and Voglmayr 1962) and should be examined in an effort to explain the different sweat losses from the scrota of Folds Plus and Folds Minus rams. V. ACKNOWLEDGMENTS Thanks are due to Dr. G. M. H. Waites and Dr. B. P. Setchell who supervised the work at the C.S.I.R.O., The Ian Clunies Ross Animal Research Laboratory, Prospect. The work was carried out during the tenure of a Public Service Board of N.S.W. post graduate fellowship at the University of New S,outh Wales, School of Wool Technology. The work was financed in part by the Wool Board. VI. REFERENCES D UN , R. B. (1964). Skin folds and Merino breeding. I. The net reproductive rates of flocks selected for and against skin folds. Australian Journal of Experimental Agriculture and Animal Husbandry 4: 376. 125 F OWLER , D. G., and D U N, R. B. (1966). Skin folds and Merino breeding. 4. The susceptibility of rams selected for a high degree of skin fold to heat induced infertility. Australian Journal of Experimental Agriculture and Animal Husbandry (in press). M W W W W , G. R., and W AITES , G. M. H. (1963). Seminal degeneration in the ram and its relation to the temperature of the scrotum. Journal of Reproduction and Fertility 5: 433. AITES , G. M. H., and M OULE , G. R. ( 1961). Relation of vascular heat exchange to temperature regulation in the testis of the ram. Journal of Reproduction and Fertility 2: 213. AITES , G. M. H., and V OGLMAYR , J. K. (1962). Apocrine sweat glands of the scrotum of the ram. Nature, 196: 965. AITES , G. M. H., and V OGLMAYR , J. K. (1963). The functional activity and control of the apocrine sweat glands of the scrotum of the ram. Australian Journal of Agricultural Research 14: 839. HITE , P., and C AUGHLEY , F. G. (1936). Seasonal variation in lambskin, with special reference to the suderiferous glands. New Zealand Journal of Science and Technology 18: 466. OUL E 126