Diurnal rhythms in testicular blood flow, testicular morphometry and reproductive hormones in Shiba goats.

Context: Testicular blood flow (TBF) is crucial for testicular function. The pattern of TBF in Shiba goats indicates seasonal variations. Aims: This study aimed to investigate the effect of diurnal variations on TBF, testis volume (TV), testicular echogenicity, and reproductive hormones in goats over a 24-h period. Methods: In three trials that went for three consecutive days each, 12 bucks were scanned using Triplex ultrasonography to assess the TV, pixel intensity of testicular echotexture (PIX), and Doppler indices of TBF (resistive index: RI and pulsatility index: PI) in four-time points a day (at 6.00, 12.00, 18.00, and 00.00 h). Concomitantly, the changes in circulating FSH, LH, inhibin, testosterone (T), estradiol (E2), cortisol, and melatonin were assessed. Key results: Results revealed diurnal alterations in the calculated RI of TBF and the PIX of testicular parenchyma (P < 0.05). Lower RI values of the TBF were observed at 6.00 h compared to other time points. There were significant diurnal alterations in the levels of FSH (P < 0.05), LH (P < 0.05), T (P < 0.0001), E2 (P < 0.0001), cortisol (P < 0.0001), and melatonin (P < 0.0001). FSH attained a higher concentration at 18.00 h compared to 12.00 h. Concentrations of LH were significantly higher at 06.00 h compared to those at 18.00 h. Concentrations of T were significantly higher at 6.00 compared to other time points. E2 showed higher concentrations at 6.00 h and 00.00 h compared to 12.00 h and 18.00 h. On the contrary, concentrations of cortisol were significantly higher at 12.00 h and 18.00 h compared to 06.00 h and 00.00 h. The highest concentrations of melatonin were observed at 00.00 h compared to other time points, while the lowest concentrations were at 12.00 h. Conclusions: Diurnal rhythm induces significant changes in TBF, testicular PIX, and circulating FSH, LH, T, E2, cortisol, and melatonin over the 24-h day. Implications: The outcomes of the study are reflected in the advisability of monitoring the TBF at a fixed time a day to avoid the circadian rhythm effect. Measuring reproductive hormones and testicular blood flow (TBF) is important to assess animal fertility. The present work investigated, for the first time, the influence of diurnal rhythmicity on TBF and hormones in goats. The findings of this study enrich the understanding of the physiological roles of reproductive hormones. They are reflected in the advisability of monitoring the TBF at a fixed time during the day to avoid the circadian rhythm effect because of the diurnal alterations in some parameters of TBF and circulating hormones, and adjusting the therapeutic approaches to infertility problems. [ABSTRACT FROM AUTHOR]