Monthly changes in testicular blood flow dynamics and their association with testicular volume, plasma steroid hormones profile and semen characteristics in rams

The present detailed study aimed to establish for the first time reference values for ultrasound measures of testicular dimensions and Doppler measures of blood flow in the testicular artery of rams over a 12-month period, and to investigate a possible association between monthly changes in dynamics of testicular blood flow from one hand and testicular volume, plasma testosterone and estradiol −17β concentrations as well as semen characteristics from the other hand. Five fat-tailed rams weighing 45-60 kg and aging 2-4 years old were subjected to semen collection, jugular blood sampling, ultrasonographic scanning of the testes and Doppler examination of testicular artery twice monthly for a period of one year. The overall mean (±SD) values for testicular volume as well as RI (resistive index) and PI (pulsatility index), respectively were 71.84 ± 5.33 mm3, 0.378 ± 0.102 and 0.642 ± 0.208. Average testicular volume was the lowest in June (59.44 ± 5.83 mm3) and reached its maximum (84.43 ± 8.52 mm3) in November after 42.2% increase (p < 0.01). Mean values of RI were lowest between September and March, increasing significantly (p < 0.01) in April (+53%) reaching highest value in June (0.564 ± 0.158). From the lowest value recorded in October through February, the average PI values increased significantly (p < 0.05) in March (+41%) to reach maximum value in July (0.940 ± 0.368). In parallel with the substantial decrease in Doppler measurements, all parameters analyzed during the breeding season (October-March) were positively affected. In conclusion, the monthly definite changes in the studied parameters evidenced three novel findings: (1) plasma testosterone concentration, which increased significantly (p < 0.05) at late summer (August), was the potential initiator for resuming the breeding season in rams via triggering spermatogenic activity and maximum testicular volume during this period, (2) resulting values of testicular volume and testicular blood flow profiles all year round provide useful reference values for predicting testicular function in rams, (3) the marked increase in testicular blood flow volume, i.e. remarkable decrease in both RI and PI values, during the breeding season could be regulated by the marked increase in testicular volume and plasma estradiol −17β levels during this period.