Reproductive performance following a modified Presynch-Ovsynch, Double-Ovsynch, or conventional reproductive management program in Korean dairy herds.

We aimed to compare the reproductive performance of dairy cattle following a modified Presynch-Ovsynch, Double-Ovsynch, or conventional reproductive management program (CRMP). On Day 30 (±5) after calving (calving = Day 0), 960 lactating cows were assigned randomly to one of two presynchronization treatments, before the synchronization of ovulation (Ovsynch) or CRMP without presynchronization. Cows were administered prostaglandin F (PGF) on Days 38 (±5) and 52, and gonadotropin-releasing hormone (GnRH) on Day 55 (Presynch-G-Ovsynch group, n = 333); or GnRH on Day 45 (±5), PGF on Day 52, and GnRH again on Day 55 (Double-Ovsynch group, n = 307). Thereafter, each cow underwent Ovsynch 7 days later: GnRH on Day 62, PGF on Day 69, and GnRH again 56 h later, followed by timed artificial insemination (AI) 16 h later. The remaining cows underwent AI when estrus was detected or Ovsynch (CRMP group, n = 320). In a subset of cows (each n = 40) in the two presynchronization groups, blood collections and ovarian ultrasonography were performed on Days 30 (±4), 52, 62, and 69, and uterine cytology on Days 30 (±4) and 52. The probabilities of pregnancy per AI 32 and 60 days after the first AI were higher in the Presynch-G-Ovsynch (odds ratio [OR]: 1.89 and 1.81, P < 0.01) and Double-Ovsynch (OR: 1.63 and 1.60, P < 0.05) groups than in the CRMP group. The likelihood of pregnancy by 210 days postpartum was higher (P < 0.05) in Presynch-G-Ovsynch (hazard ratio [HR]: 1.29) and Double-Ovsynch (HR: 1.31) groups than in the CRMP group, whereas the least square mean number of inseminations per conception was lower (P < 0.05) in Presynch-G-Ovsynch (1.8) and Double-Ovsynch (1.8) groups than in the CRMP group (2.1). The percentages of cows with serum progesterone concentrations ≥1.0 ng/mL or with a corpus luteum (CL) did not differ between the groups (P > 0.1) on Days 30, 62, and 69, but were lower (P < 0.05) on Day 52 in the Presynch-G-Ovsynch than in the Double-Ovsynch groups. However, the diameter of the dominant follicles, the proportion of neutrophils in uterine cytological samples, and the prevalence of an accessory CL on Day 69 did not differ (P > 0.1) between the two groups. In conclusion, both the Presynch-G-Ovsynch and Double-Ovsynch programs improved reproductive performance vs. CRMP in smallholder Korean dairy herds, and there were no differences in the ovarian endocrine and structural dynamics, or uterine health, between the two programs involving presynchronization.