The testicular vascular cone, scrotal thermoregulation, and their relationship to sperm production and seminal quality in beef bulls

The objectives of the present study were to determine changes with age and relationships among characteristics of the testicular artery, scrotal surface temperature, scrotal circumference, testicular consistency, seminal quality and sperm production. Beef bulls aged 6 mo (n=12), 1 yr (n=12), 2 yr (n=11), and 3 yr (n=12) were used in this study. The mean length of the testicular artery as well as the length, width, and surface area of a latex cast of the testicular artery all increased between 6 mo and 1 yr of age (P<0.01). Wall thickness of the testicular artery and testicular arterial-venous distance in the spermatic cord decreased with age and with proximity to the testicle (P<0.01). Distance from the testicular vascular cone to the inner surface of the skin at the top of the scrotal neck (primarily fat) increased between 1 and 3 yr of age (P<0.01), and was associated with an increased top scrotal surface temperature (P<0.09). Increased epididymal sperm reserves were associated with an increase in testicular consistency, scrotal circumference and scrotal surface temperature gradient, and with a decrease in testicular arterial wall thickness and testicular vascular cone to skin distance. A decrease in sperm defects was associated with an increase in testicular consistency and with a decrease in the average scrotal surface temperature. Increased sperm motility was associated with increased scrotal circumference and a decreased top testicular vascular cone to skin distance. These findings emphasize the importance of thermoregulation to sperm production and seminal quality.