Testicular blood flow in the stallion: Variability and its relationship to sperm quality and fertility

Abstract

The aim of this study was to investigate if Colour Doppler sonography of the testicular artery is a reliable method for the measurement of testicular blood flow in stallions. Furthermore, time dependent (daily, seasonal) variations in testicular blood flow, the effects of sexual activity, and the relationship between testicular blood flow and sperm production as well as fertility was examined. In total 40 stallions with a mean age of 9.1 ± 4.2 years were investigated between July 2002 and January 2003. All animals were used for semen collections until July 2002 and afterwards they had 8 weeks of sexual rest. Between October 2002 and January 2003 24 stallions (DR) continued sexual rest whereas in 16 stallions (DE) semen collections were carried out three times a week on days Monday, Wednesday and Friday for cryopreservation of semen. Blood flow was quantified by using the Pulsatility Index (PI) and Blood Flow Volume (BFV). Both parameters, PI- (median: 2.2; median absolute deviation (MAD): 0.6; min.: 0.8; max.: 6.4) as well as BFV-values (median: 33.4 ml/min; MAD: 6.5 ml/min; min.: 14.9 ml/min; max.: 80.4 ml/min) varied distinctly. PI and BFV were not related to each other (r=-0.10; p>0.05). Intra-class correlation coefficients for repeated examinations were relatively high (PI: 0.82; BFV: 0.85). There were no variations (p>0.05) of PI and BFV between different daytimes and consecutive weeks (p>0.05). BFV showed no variations between July, October and January (p>0.05), whereas PI decreased between October and January (p < 0.05). No relationships (p > 0.05) could be observed between PI and sperm quantity, sperm quality, respectively, but a positive correlation was noticed between BFV and total sperm number per ejaculate (r=0.56; p<0.05). Neither BFV nor PI were related to fertility parameters (p>0.05). The results show that Colour Doppler ultrasonography is a reliable method for assessing testicular blood flow in stallions. Concerning total sperm production testicular blood flow volume has some predictable value, but in fertile stallions, there are no relationships between PI and sperm quality as well as fertility.