Abstract

The purpose of this study was to assess the ovarian follicle diameter and hormone status during early postpartum in cows. Eighteen Holstein cows, aged 3.5–5.5 years and of 400–600 kg BW with normal calving, were examined every 3rd day starting from Day 15 until Day 33 postpartum. Blood samples for hormonal (progesterone (P4) and estradiol-17β (E2)) analyses were withdrawn from the coccygeal vein every 3rd day until the end of the experiment. The ovarian follicular number and size were verified and measured using a sector vaginal transducer ultrasound scanner (6.5 MHz probe, SA 600; Medison Co., Seoul, Korea). The least squares means (±SEM) are presented for each day (GLM of SAS). In postpartum cows, E2 levels were 27.09 ± 5.22 pg, 24.50 ± 5.76 pg, 26.92 ± 4.62 pg, 25.53 ± 3.74 pg, 27.47 ± 5.72 pg, 26.48 ± 8.06 pg for Days 15, 18, 21, 24, 27, 30, and 33, respectively, 28.01 ± 7.52 pg; P4 levels were 1.35 ± 1.14 ng, 2.41 ± 1.70 ng, 2.85 ± 2.26 ng, 2.88 ± 1.90 ng, 2.91 ± 1.91 ng, 3.04 ± 2.31 ng, and 4.04 ± 3.70 ng for Days 15, 18, 21, 24, 27, 30, and 33, respectively. The ovarian follicle diameter was 12.36 ± 3.31 mm, 11.91 ± 2.99 mm, 13.09 ± 3.37 mm, 13.55 ± 2.76 mm, 14.55 ± 3.68 mm, 15.64 ± 5.53 mm, 17.45 ± 3.22 mm for Days 15, 18, 21, 24, 30, and 33, respectively. The present results show that mean plasma concentration of P4 and mean follicle diameter gradually increased from Day 15 to Day 33 postpartum. It is concluded that monitoring of P4 and E2 during early postpartum period would be useful to predict the ovarian starts for early rebreeding in dairy cows.