Effect of seasonality on testicular blood flow as determined by color Doppler ultrasonography and hormonal profiles in Shiba goats

The objectives of this study were to determine if there is a seasonal pattern of testicular blood flow in male Shiba goats, and ascertaining whether or not there is a relationship among changes in testicular hemodynamics and circulating testosterone (T) and estradiol (E2). Twelve sexually mature male Shiba goats (Capra hircus), aged 19.5 ± 2.5 months were used in this study. Monitoring of the changes in testicular blood flow was performed once a week for 1 year, using color spectral Doppler ultrasonography. Plasma concentrations of testosterone (T) and estradiol (E2) were determined by radioimmunoassay. Among the four seasons, the greatest increases (P ≤ 0. 001) in the values for the resistive index (RI) and pulsatility index (PI) of the testicular artery were recorded in the summer. Also, PI and RI values recorded in spring were greater than those recorded in autumn, while for winter there were the least values for these indices. Likewise, concentrations of T and E2 showed seasonal changes. Concentrations of T and E2 were greater during the autumn and winter compared to those in spring and summer. Interestingly, E2 concentrations were negatively associated with Doppler indices of the testicular artery. In conclusion, although Shiba goats are considered to be non-seasonal breeding animals, there were distinct seasonal patterns of testicular blood flow as measured by color Doppler ultrasonography, especially in Doppler indices. These changes were coincident with the changes in the circulating E2 and may be attributable to the seasonal changes in ambient temperature or daylight length.