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 F2α (PGF2α) 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), PGF2α 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, PGF2α 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.

中文翻译：

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在韩国奶牛群中采用改良的 Presynch-Ovsynch、Double-Ovsynch 或传统繁殖管理程序后的繁殖性能

我们旨在比较采用改良 Presynch-Ovsynch、Double-Ovsynch 或传统繁殖管理程序 (CRMP) 后奶牛的繁殖性能。在产犊后第 30 (±5) 天（产犊 = 第 0 天），在排卵同步 (Ovsynch) 或 CRMP 之前，将 960 头泌乳奶牛随机分配到两种预同步处理之一。在第 38 (±5) 天和第 52 天给奶牛注射前列腺素 F2α (PGF2α)，在第 55 天注射促性腺激素释放激素 (GnRH)（Presynch-G-Ovsynch 组，n = 333）；或第 45 天 (±5) 的 GnRH、第 52 天的 PGF2α 和第 55 天的 GnRH（双 Ovsynch 组，n = 307）。此后，每头奶牛在 7 天后接受 Ovsynch：第 62 天的 GnRH，第 69 天的 PGF2α，56 小时后再次进行 GnRH，16 小时后进行定​​时人工授精（AI）。其余奶牛在检测到发情或 Ovsynch（CRMP 组，n = 320）时接受 AI。在两个预同步组的一部分奶牛（每头 n = 40）中，在第 30 (±4)、52、62 和 69 天进行采血和卵巢超声检查，在第 30 (±4) 天和第 69 天进行子宫细胞学检查。 52. 在第一次 AI 后 32 天和 60 天，每个 AI 的怀孕概率在 Presynch-G-Ovsynch（优势比 [OR]：1.89 和 1.81，P < 0.01）和 Double-Ovsynch（OR：1.63 和 1.60）中更高, P < 0.05) 组比在 CRMP 组中。Presynch-G-Ovsynch（风险比 [HR]：1.29）和 Double-Ovsynch（HR：1.31）组在产后 210 天的怀孕可能性高于 CRMP 组（P < 0.05），而最小二乘法Presynch-G-Ovsynch (1. 8) 和 Double-Ovsynch (1.8) 组比在 CRMP 组 (2.1) 中。在第 30、62 和 69 天，血清黄体酮浓度≥1.0 ng/mL 或具有黄体 (CL) 的奶牛百分比在各组之间没有差异 (P > 0.1)，但在Presynch-G-Ovsynch 组的第 52 天比双 Ovsynch 组多。然而，优势卵泡的直径、子宫细胞学样本中中性粒细胞的比例以及第 69 天辅助 CL 的患病率在两组之间没有差异（P > 0.1）。总之，与 CRMP 相比，Presynch-G-Ovsynch 和 Double-Ovsynch 计划都提高了韩国小规模奶牛群的繁殖性能，并且两个涉及预同步化的计划在卵巢内分泌和结构动力学或子宫健康方面没有差异.