Scrotal Heat Research Articles

Effect of scrotal heating on testicular enzymes and spermatogenesis in the rat.

Immersion of the scrotal testis of the rat in water at 42�C for 30 min caused rapid damage to pachytene primary spermatocytes in stages 1, 2, 3, and occasionally 8 of the seminiferous epithelium. There was cytoplasmic chromophilia with eosin or Alcian blue and binding of the fluorescent dye 2-p-toluidinylnapthalene-6-sulphonate to the cell membranes. Rapid dissolution of damaged cells occurred and most had disappeared by 28 hr after heating. Early round spermatids also showed nuclear changes with vacuolation and the development of "signet ring" nuclei.

Metabolic, respiratory and vasomotor responses to heating the scrotum of the ram.

1. Oxygen consumption, respiratory frequency, and temperatures of the rectum, common carotid artery, external auditory meatus, and skin on the ears, near the distal end of the metacarpus and metatarsus, upper thigh and mid-side of the body, were measured in five rams before, during and after heating the scrotum. Effects on the woolly animal exposed to ambient temperatures of 17-19 degrees C, and on the shorn animal exposed to ambient temperatures of 5.6-24.5 degrees C, were determined.2. In eight experiments on woolly animals scrotal heating resulted in vigorous panting and a lowering of deep body temperatures by 0.3-1.1 degrees C within 50 min. There was no significant change in oxygen consumption or body skin and upper thigh temperature. Changes in skin temperature of the extremities indicated, on average, a vasodilator response to heating. However, individual responses were unpredictable, there sometimes being dilation and constriction in different extremities of the same animal.3. In twelve experiments on shorn animals in environments below 20 degrees C, oxygen consumption before scrotal heating was higher than when the animal was woolly. Scrotal heating resulted in a fall in oxygen consumption and a lowering of deep body temperatures by 0.2-0.9 degrees C within 50 min. There was no change in respiratory frequency or body skin and upper thigh temperature. As in the woolly animal, vasomotor responses were disorganized, although there was a tendency towards vasodilation.4. In three shorn animals in environments of 20.5 and 24.5 degrees C, oxygen consumption before scrotal heating was only slightly higher than when the animal was woolly. In two of these animals (in 20.5 and 24.5 degrees C) scrotal heating resulted in a slight lowering of oxygen consumption and mild panting, and deep body temperature fell by 0.9 degrees C in 50 min. In the third animal (in 24.5 degrees C) there was no change in oxygen consumption but vigorous panting and vasodilation, and deep body temperature fell by 1.3 degrees C in 50 min.5. In a number of experiments on shorn animals scrotal heating was continued for more than 100 min. Deep body temperature was controlled at a new low level after the initial fall, and the possibility of a resetting of the ;set-point' temperature is discussed.6. The previously unexplained fall in body temperature of the shorn ram in which panting did not follow scrotal heating may now be mainly ascribed to a reduction in metabolic rate. Also, the possible role of cutaneous evaporation should not be discounted. The inhibition of panting in the shorn sheep at environmental temperatures below 20 degrees C remains unexplained.7. Body heating alone, by covering the shorn animal with a sheep skin coat in an environment of 19 degrees C, elicited well organized vasomotor changes in the ears and lower legs.8. As a result of the present study and previous work by others, it is clear that all thermoregulatory mechanisms, with the exception of vasomotor changes, may be influenced in a predictable manner by temperature changes of the scrotum.

Selecting Merino rams for ability to withstand infertility caused by heat. 1. Anatomy and functional activity of the scrotum

Merino rams selected for (Folds Plus) and against (Folds Minus) skin wrinkle have been used in a study of scrotal heat tolerance. The type selected against skin wrinkle (Folds Minus) showed a higher scrotal fluid loss and sweat gland and fibre density than the Folds Plus type. Folds Minus rams had smaller scrotal sweat glands which discharged more frequently than those of the Folds Plus rams during early periods of scrotal heating. Scrotal heat tolerance was seen to increase with increases in scrotal surface area. These findings are discussed in terms of the light they shed on the problem of identifying the features that characterize high scrotal heat tolerance in Merino rams

Selecting Merino rams for ability to withstand infertility caused by heat. 2. The effect of heat on scrotal and testicular blood flow

Rams selected for and against skin wrinkle (Folds Plus and Folds Minus) are known to differ in their susceptibility to infertility caused by heat. Rams of these types were therefore subjected to heat and the differences in their reactions studied in an attempt to cast light on the mechanisms involved in scrotal heat tolerance. An experiment to investigate the relationship between the degree of heat load to the scrotum and testes to ram fertility suggested that the scrotum and perhaps also the testes play an active role in modifying the damaging effects of high temperature. One of the factors that could influence the amount of heat reaching the testes is scrotal blood flow and this was found to increase with increases in scrotal temperature. Folds Minus rams showed greater increases than Folds Plus rams but only after 2.5 hours at a scrotal temperature of 40�C. In all rams the lower regions of the scrotum showed a greater increase in blood flow than upper regions. Folds Plus rams showed no increase in testicular blood flow as temperature increased but Folds Minus rams showed an increased testicular blood flow at 40�C.

Effects of scrotal heating in the ram on semen characteristics, fecundity, and embryonic mortality

In three experiments the testes of rams were heated to 40.5�C for either 1.5 hr or 2 hr, or to 39.5�C for 4 hr; the effect on the number of spermatozoa in the ejaculate and the proportion of these that were dead or tailless was examined over the subsequent 60 days. The fecundity of the rams was tested over the same period and compared with that of the unheated rams, a total of 396 ewes being used. Spermatozoa present in the epididymis at the time of heating appeared to be unaffected, but there was considerable damage to spermatozoa developing in the testes. This was manifested by increased proportions of dead and of tailless spermatozoa between days 14 and 50 (day 0 = day of heating). In rams whose testes were heated to 40.5�C there was also a marked depression in the number of spermatozoa per ejaculate between days 34 and 47, and their fecundity was low between days 14 and 34 and was zero between days 34 and 47. Embryonic losses were estimated by comparing the number of eggs fertilized (in ewes 2 days post coitum) with the number of embryos present in ewes examined 37-42 days post coitum. In only one of the three experiments was there a significantly increased loss of embryos in ewes mated to heat-treated rams. It is concluded that, in ewes mated to heat-treated rams, embryonic losses are of minor importance compared with losses due to non-fertilization.