Testicular vascular cone development and its association with scrotal temperature, semen quality, and sperm production in beef bulls

The objectives of this study were to characterize development of the testicular vascular cone using ultrasonography and to determine associations of vascular cone morphology with scrotal temperature, semen quality, and sperm production. Beef bulls (n = 70) were examined from 10 to 70 wk of age in two years, and a third group of bulls (n = 44) was examined only at 74 wk of age. Testicular vascular cone diameter increased until approximately 13.5 mo of age, or until 1 to 8 wk before maximum scrotal circumference was observed. Vascular cone fat thickness also increased with age and followed a pattern similar to that observed for backfat. Testicular artery wall thickness and the distance from the arterial to the venous blood in the vascular cone decreased with proximity to the testis. Vascular cone diameter was negatively correlated with scrotal surface temperatures and with the percentage of sperm head defects and detached sperm heads, but positively correlated with the percentage of normal sperm. The arterial–venous blood distance was negatively correlated with the percentage of normal sperm and positively correlated with percentage of sperm head defects and proximal droplets. In conclusion, testicular vascular cone diameter increased with age following testicular development, whereas vascular cone fat thickness increased similar to a pattern observed for backfat. Increased testicular vascular cone diameter and decreased distance between arterial and venous blood were associated with increased percentage of normal sperm and decreased percentages of sperm defects.