Abstract: This study investigated the effect of grape pomace extract (GPE) on luteinizing hormone (LH), testosterone (T) and estradiol (E2) concentration in serum of Hu rams. Twenty-four Hu rams weighing (22.74±0.23 kg) were randomly divided into three groups (n=8). A control group of rams were fed a basal diet containing 4% linseed oil, while T₁ and T₂ groups were fed the basal diet supplemented with 0.36% and 0.72% GPE, respectively. The experiment duration was 81 days, comprising a 7-day pre-trial period, a 14-day transition period, and a 60-day formal experiment. At the conclusion of the feeding experiment, the rams were slaughtered and relevant data collected. The results showed: 1) supplementation with GPE did not significantly affect body weight (P>0.05). 2) Compared with the control group, supplementation with 0.72% GPE in diets significantly increased testicular weight (233.02±32.67 g vs. 347.82±31.82 g, P<0.05), testicular volume (255.50±40.55 mL vs. 365.63±32.41 mL, P<0.05), a testicular size index (0.61±0.10 vs. 0.92±0.09, P<0.05), diameter of seminiferous tubules (160.02±7.55 μm vs. 220.25±6.69 μm, P<0.05) and epididymis weight (45.53±4.00 g vs. 54.38±4.03 g, P=0.088). However, there was no significant difference between T₁ and control groups (P>0.05), except for the diameter of seminiferous tubules (160.02±7.55 μm vs. 182.76±8.26 μm, P<0.05). 3) Compared with the control group, the expression of steroidogenic acute regulatory protein and luteinizing hormone receptor genes in group T₂ was significantly up-regulated (P<0.05), while the cytochrome P450 family 19 subfamily A member 1 expression was inhibited (P<0.05). 4) The concentration of testosterone in group T₂ was significantly higher than in the control group (803.22±145.74 pg·mL^-1 vs. 575.09±57.58 pg·mL^-1, P<0.05), while the concentration of LH in group T₂ was decreased (0.05±0.01 IU·L^-1 vs. 0.11±0.03 IU·L^-1, P<0.05). The T₁ treatment did not significantly affect LH, T and E2 concentrations (P>0.05). In conclusion, the supplementation of 0.72% GPE in diets improved testis development during peri-puberty by regulating testosterone synthesis in Hu rams.

Key words: grape pomace extract, reproductive hormones, puberty, Hu sheep