To determine the effects of Follicle Stimulating Hormone (FSH) treatment and subsequent withdrawal on uterine proliferation and estrogen receptor (ESR), Brahman crossbred heifers (n = 12) were twice daily injected with FSH (4, 3, and 2 mg/injection) on Days 17–19 of the estrous cycle (FSH 3 days) and (4 and 3 mg/injection) on Days 17–18 (FSH 2 days) and withdrawal with saline on Day 19 and (4 mg/injection) on Day 17 (FSH 1 day) and withdrawal with saline on Days 18–19. Uterine tissue was subjectively collected on Day 20 and microscopically classified to four regions: endometrial stroma (ES), surface endometrial gland (EG), deep endometrial gland (DG), and myometrium (Myo). The cell proliferation marker, Ki‐67, was quantified as labeling index (LI) in uterine regions, and tissues were immunostained to detect ESR2 followed by image analysis. The LI of ES, EG, and DG was greater (P = 0.0018, P = 0.0005, and P = 0.0103; respectively) in heifers received FSH for 3 days. The expression of ESR2 protein on ES and EG was greatest (P < 0.0001 and P = 0.0036, respectively) in FSH 3 days‐treated group. Thus, FSH administration during proestrus stimulates uterine cell proliferation, and ESR2 expressions are affected by FSH during proestrus and differentially distributed in the uterine regions.

Supplementation of organic trace mineral (OTM) may affect reproductive functions in several aspects and has been studied, but very rare is reported in dairy cows. To determine the effects of dietary OTM supplement during pre- and postpartum with timed artificial insemination (TAI) protocol on steroid hormones, antioxidant enzymes, and reproductive performances in dairy cows. Prepartum Holstein cows (n = 60) were randomly assigned to received either a control diet or OTM supplemented for 42 days. Both groups were fed the same total mixed ration, but were supplemented with 5 g/head/d OTM (Bioplex®) in the treatment group. Blood and follicular fluid samples were collected to determine progesterone (P4), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and estradiol (E2) concentrations. Cows fed OTM had better placental expulsion period, milk yield, and reproductive performance parameters (day to first ovulation and estrus, percentage of first estrus and size of preovulatory follicle) than control cows (P < 0.05). Cows fed OTM affected (P < 0.05) the serum concentration of P4 on days 12, 15, 18, 21, and 42 after TAI. Follicular fluid concentrations of E2 in large follicle in OTM cows were greater than control cows (336.3 and 376.9 ng/mL; P < 0.05). Cows supplemented with OTM had greater serum SOD and GSH-Px activities than control cows (15.5 vs. 10.6 U/mL and 12.1 vs. 9.9 U/mL; P < 0.05). In conclusion, supplements with OTM improved uterine and placental health, steroid hormones concentrations, and antioxidant enzyme activities but did not improve conception rate in dairy cows.