Ultrasonographic measurement of stallion accessory sex glands and excurrent ducts during seminal emission and ejaculation

Accessory sex gland and excurrent duct activity of 10 stallions was visualized with transrectal ultrasonography during seminal emission and ejaculation. First and last penile urethral contractions were defined as the start (O sec) and end of ejaculation, respectively. Duration of ejaculation (n = 63 ejaculations) averaged 6.15 +/- 2.98 sec. Penile urethral contractions occurred an average of 6.2 +/- 2.2 times per ejaculation. Right bulbourethral glands (n = 19 ejaculations) alternated repeatedly from ovoid to flattened, irregular shapes during ejaculation. Cross-sectional area of right bulbourethral glands did not change (p > 0.40) between 3 sec before ejaculation and the end of ejaculation. Cross-sectional area of right prostatic lobes (n = 17 ejaculations) decreased (p < 0.01) between 3 sec before ejaculation and the end of ejaculation, with decreases (p < 0.05) at 2, 1, and 0 sec before ejaculation and at the time of the second penile urethral contraction. Excurrent ducts of ampullae (n = 17 ejaculations) first appeared to dilate with fluid at 2.60 +/- 0.23 sec before ejaculation and subsequently dilated an average of 3.4 +/- 0.3 times between 3 sec before ejaculation and the end of ejaculation. Fifty-three of 58 (93%) ampullar duct dilations occurred prior to the start of ejaculation. During each dilation of ampullar ducts, fluid remained visible for 0.23 +/- 0.04 sec. Fluid was detected within the lumina of vesicular gland excurrent ducts during the 6 of 17 monitored ejaculations that produced detectable gel. First and last dilations of vesicular gland ducts began at 1.31 +/- 0.58 and 5.12 +/- 0.96 sec, respectively, and a total of 4.3 +/- 0.7 dilations occurred between 3 sec before ejaculation and the end of ejaculation. During each dilation of vesicular gland ducts, fluid remained visible for 0.73 +/- 0.21 sec.