Abstract
Letrozole (LTZ) is an aromatase inhibitor that limits estrogen (E2) production and increases testosterone (T) levels. This research aimed to examine the impact of a single dose of LTZ on testicular hemodynamics, ejaculation time, and semen quality in goats under heat stress (HS). Therefore, Doppler examination and semen evaluation were performed on twelve mature bucks for two weeks (W-1, W-2) as pre-heat stress control during winter. Then during summer HS bucks were subjected to Doppler examination, semen evaluation, and hormonal analysis (T, E2, and LH) at 0 h. Afterward, bucks were assigned into two groups and subcutaneously injected with physiological saline (n = 6; CON) or LTZ (0.25 mg/kg BW; n = 6; LTZ). Both groups were subjected to Doppler scanning and hormonal analysis at 2, 4, 24, 48, 72, 96,144, and 168 h. Semen evaluation was performed at 48 and 168 h. The LTZ group showed increasing (P < 0.05) in semen volume, sperm motility, and viability and decreasing (P < 0.05) in ejaculation time and sperm abnormalities compared to CON group at 48 h. Additionally, T concentrations increased (P < 0.01) at 2, 24, and 48 h, E2 decreased (P < 0.01) from 2 to 48 h, and LH raised (P < 0.01) at 2 and 72 h in LTZ group compared to CON one. Doppler indices reduced (P < 0.05) at 96 h in LTZ group. semen pH and scrotal circumference were not affected by LTZ. In conclusion, LTZ administration shortened ejaculation time and enhanced semen quality in bucks during HS.