Table 1.
Summarizing the factors that could affect testicular blood flow in farm and companion animals
| Factor | Findings | Species | References |
|---|---|---|---|
| Thermal factor | • Significant increases in TBF were found in response to increases in ambient temperature | Angus bulls | Barros Adwell et al. 2018 |
| • Direct applying heat to the testis induced increases in TBF up to 26% | Rams | Mieusset et al. 1992 | |
| • Warming the testes from 34 °C to 40 °C led to notable increases in the TBF | Bulls | Rizzoto et al. 2020 | |
| • Decreases in TBF were reported during the summer season (29.43 ± 1.45 °C) compared with those found in the winter season (m 10.38 ± 1.02 °C) | Shiba bucks | Samir et al. 2018 | |
| • No changes in the TBF were reported when the average temperature of the scrotal surface increased (> 3 °C) | Dogs | Henning et al. 2014 | |
| • Artificial cooling of testes induced marked reductions in scrotal blood flow without any effect on TBF | Dogs | Glode et al. 1984 | |
| • Experimental warming of the testes (to 40 °C) resulted in an extreme increase in TBF | Bulls | Rizzoto et al. 2020 | |
| • Exposing the testes to the scrotal insulation for up to 120 h resulted in alterations in testicular temperature, the velocity of the TBF, and seminal quality | Bulls | Barca Junior et al. 2020 | |
| Seasonal factor | • Increases in TBF have been reported in spring months as compared to winter months and these alterations in TBF were coincident with sperm production (Boyd et al. 2006) | Stallions | Boyd et al. 2006; Pozor 2007 |
| • The highest TBF (evidenced by the lowest RI values of the supratesticular artery) was found during the breeding season (from September to March), reduced significantly from April to June. Concomitantly, testosterone, estradiol, and semen parameters were positively affected during the breeding season | Rams | Hedia et al. 2019 | |
| • The season had a nonsignificant effect on the testicular hemodynamics | Rams | Noordhuizen-Stassen et al. 1985 | |
| • A typical seasonal change in testicular volumes (with a maximum volume in September), testosterone levels (peak levels in December), and TBF (highest perfusion in September; the lowest RI values) all over the year | Sarda bucks | Strina et al. 2016 | |
| • Seasonal alterations in TBF because the values of Doppler indices (RI and PI) of the testicular artery showed the greatest increases in the summer (June to August), whereas the lowest values for these indices were reported in winter (December to February). Similarly, the PI and RI values in autumn (September to November) were less than those recorded in spring (March to May), | Shiba bucks (nonseasonal animal) | Samir et al. 2018 | |
| • Characterization of the normal blood flow of the testicular arteries over a long duration showed no statistically significant differences | Dogs | Carrillo et al. 2012 | |
| Species | • The waveforms of blood flow (either at the level of the STA or MTA) of canine, caprine, ovine, and cattle testes appear to have monophasic and non-resistive characteristics. On the opposite, TBF in stallions is often characterized by resistive-biphasic waveforms at the extent of the spermatic cord and non-resistive, monophasic frequencies from the MTA | Dogs, bucks, rams, bulls, stallions | Günzel-Apel et al. 2001; Gumbsch et al. 2002; Samir et al. 2015; Camela et al. 2019; Fadl et al. 2022; Claus et al. 2019; Rodrigues et al. 2020; Pozor and McDonnell 2004 |
| • It was revealed the appearance of a biphasic high-resistance blood flow within the proximal segment of the STA in dogs, similar to that observed in the STA of stallions | Dogs | Carrillo et al. 2012 | |
| Breeds | • The TBF parameters were evaluated for 334 bulls of five different breeds (Nellore, Aberdeen Angus, Hereford, Bradford, and Brangus) and showed differences among the evaluated breeds in the MV and RI of the bulls’ STA. Brangus bulls showed significantly higher values of TAMAX (16.3 ± 1.0 cm/s) as compared with the Nelore bulls (8.8 ± 0.4 cm/s). Higher RI values were found in Hereford (0.44 ± 0.01) compared with Brangus (0.36 ± 0.02) animals, whereas the PI values did not differ among breeds. In addition, there was no significant change in the PI or RI values of Nelore bulls compared with bulls of other B. taurus breeds (Angus, Bradford, Brangus, and Hereford) | Bulls | Junior et al. (2018) |
| • Significantly greater values of PI and RI of the testicular arteries in bulls of the Nelore breed were found as compared with Caracu bulls | Bulls | Rodrigues et al. 2020 | |
| • Differences in the Doppler velocimetry parameters of TBF have been found between dogs of different breeds and sizes (small dogs such as French Bulldog and large dogs such as Labrador, Rottweiler, and German Shepherd). Higher velocities (especially the EDV) of blood flow were recorded in the spermatic cord in large dogs, but the Doppler velocity values were higher at the MTA in small breed dogs | Dogs | Souza et al. 2014 | |
| Puberty or Age effect | • PSV and EDV values of the blood flow within the testicular artery were significantly lower in prepubertal dogs as compared with postpubertal dogs | Dogs | de Souza et al. 2015a |
| • Age had no significant effect on TBF in stallions, however, decreased values of EDV and increased values for RI were reported in old stallions than in the middle-aged stallions in the STA region | Stallions | Pozor and McDonnell 2004 | |
| • Decreased RI values were found at sexual maturity in rams | Rams | El-Sherbiny et al. 2022e | |
| • There were no significant variations in TBF Doppler indices between young and adult bulls or between pre-and postpubertal mature rams | Bulls and rams | Gloria et al. 2018; Elbaz et al. 2019 | |
| • It was reported lower values of RI and PI of the examined STA in the mature (0.32 ± 0.04 and 0.36 ± 0.03, respectively; 2.5 years) and aged rams (0.51 ± 0.03 and 0.77 ± 0.06, respectively; 7.5 years) compared to the young ones (0.62 ± 0.03 and 0.98 ± 0.07, respectively; age 1 year) | Rams | Hedia and El-Shalofy (2022) | |
| Bodyweight of the animal | • Greater TBF (lower Doppler indices values) was recorded in heavy horses as compared with miniature horses | Stallions | Ortega-Ferrusola et al. 2014 |
| Sexual activity | • Increased sexual activity has a positive effect on TBF | Stallions | Ortega-Ferrusola et al. 2014 |
| Testicular laterality | • Most studies on bucks, rams, and stallions have revealed a lack of significant differences between the right and left testes in terms of pulsed-wave Doppler indices | Bucks, rams, and stallions | Samir et al. 2015, 2018; Mandour et al. 2020; Pozor and McDonnell 2004; Camela et al. 2017; Elbaz et al. 2019 |
| • In Awassi rams, RI and PI were a bit increased (P ˂ 0.05) in the right testicular artery as compared with the left one | Rams | Hedia et al. 2020b | |
| • In dogs of various breeds and weights, the left testis is substantially larger than the right one, whereas the Doppler velocity parameters and indices did not differ between the sides | Dogs | Souza et al. 2014; de Souza et al. 2015a | |
| Diseases and reproductive disorders | • Various diseases such as testicular torsion and varicocele in stallions and testicular tumors in dogs may induce alterations in testicular hemodynamics | Stallions and dogs | Pozor and McDonnell 2004; Pozor 2007; Bigliardi et al. 2019 |
| The section of the artery evaluated | • The PSV, EDV, and RI values of the STA were significantly higher than those in the MTA and were higher in the MTA as compared with those in the intratesticular branches | Bulls | Gloria et al. 2018 |
| • Doppler indices (RI, PI) were significantly higher in the STA compared with those in the MTA | Bucks and donkey | Samir et al. 2020a, b; Gacem et al. 2020 | |
| • Significant differences were found in Doppler parameters of TBF (PSV, EDV, RI, and PI values) measured in five regions along the testicular artery (STA [proximal, medial, and distal regions], MTA, and intratesticular branches). The RI, PI, and PSV values decreased gradually along the course of the testicular artery. The highest values were noted in the cranial segment of the STA, which decreased gradually in the other sections, whereas the lowest values were measured within the intratesticular arteries | Dogs | Carrillo et al. 2012; de Souza et al. 2015a, b; Trautwein et al. 2019 | |
| • Morphological and hemodynamic changes were reported in different regions of the STA. Higher PSV, RI, and PI were found in the proximal region of the STA, followed by middle and distal ones. Also, significant progressive increases in the TABF and TABFR were found along the testicular cord until entering the testis | Assaf rams | Hassan et al. 2022 | |
| Psychological status of the patient | • Some animals such as dogs may experience tremors and fear, which can interfere with the Doppler examination | Dogs | Trautwein et al. 2019 |
| Diurnal effect | • Diurnal rhythm induces significant changes in TBF over the 24 h a day | Bucks | Samir et al. 2022 |
Abbreviations: TBF Testicular blood flow; PSV Peak systolic velocity; EDV End diastolic velocity; TAMAX Time average maximum velocity; RI Resistive index; PI Pulsatility index; TABF Total arterial blood flow; TABFR Total arterial blood flow rate