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Regulation of testicular temperature is dependent on several features. Scrotal skin is typically thin, with minimal hair and an extensive subcutaneous vasculature, facilitating heat loss by radiation [3]. The scrotal neck is the warmest part of the scrotum; a long distinct scrotal neck (and pendulous scrotum) reduces testicular temperature by increasing the area for radiation and enabling the testes to move away from the body. The tunica dartos, a thin sheet of smooth muscle under the scrotal skin, is controlled by sympathetic nerves and contracts and relaxes in cold and warm environments, respectively [4]. The cremaster muscle also contracts to draw the testes closer to the body under cold ambient conditions [4]. Dorsal to the testis is the testicular vascular cone [5], consisting of the highly coiled testicular artery surrounded by the pampiniform plexus, a complex venous network. The testicular vascular cone functions as a classic countercurrent heat exchanger, transferring heat from the artery to the vein, contributing to testicular cooling. Characteristics of scrotal surface temperatures and the testicular vascular cone in bulls aged 0.5–3 years were reported [6]. As bulls age, testicular vascular cone diameter increased; furthermore, increases in testicular vascular cone diameter and a shorter distance between arterial and venous blood in this structure were associated with increased percentage of normal sperm and fewer sperm with defects [7]. In a comparative study of semen quality and scrotal/testicular thermoregulation in Bos indicus, Bos taurus, and B. indicus/B. taurus crossbred bulls, there were significant differences among these genotypes in the vascular arrangement, characteristics of the testicular artery (e.g. wall thickness), and thickness of the tunica albuginea; overall, B. indicus bulls had the best thermoregulatory capacity whereas B. taurus bulls had the worst, with crossbred bulls intermediate [8].

Sweating and whole‐body responses also contribute to testicular cooling. In bulls, sweat gland density is highest in the scrotal skin [9]. In rams, apocrine sweat glands in the scrotum discharge simultaneously (up to 10 times per hour) when scrotal surface temperature is ~35.5 °C [10]. In these animals, respiration rate increases in association with scrotal surface temperature, reaching 200 breaths per minute when scrotal surface temperature is 38–40 °C [11].