The objective of this randomized, controlled study was to evaluate the reproductive and economic performance of dairy Holstein heifers managed for first to third artificial inseminations (AIs) with or without an intravaginal progesterone device (IPD) under different temperature-humidity indexes (THI) and combined with AI after observed estrus. A total of 503 heifers from one rearing commercial farm were randomly assigned for first AI to the 5d Co-synch 72 h protocol (5dCO; n=261) or to the 5d Co-synch protocol plus IPD (5dCOP4; n=242). In a subset of heifers (n = 193) we determined progesterone (p4) and performed an ovarian ultrasound scanner on Days 0, 5, 8 and 15. Animals were considered to be synchronized on Day 5 if p4 > 1 ng/mL and a corpus luteum present; synchronized on Day 8 if p4 < 1 ng/mL, luteolysis and a follicle > 8 mm diameter was observed; and synchronized on Day 15 if p4 > 1 ng/mL and ovulation occurred, defined as the presence of a CL in the ovary where a follicle had been detected on Day 8. Pregnancy diagnosis was performed by ultrasound scanner on Days 28-35 after AI. The diagnosis confirmation was done by ultrasound on Days 50-56 and again on Days 100-113 after AI. Non-pregnant heifers (n=205) were resynchronized with the same protocol for second fixed-time AI (FTAI) and 104 for third FTAI. Pregnancy per AI (P/AI) and pregnancy loss after each AI were calculated. Reproductive costs were calculated at the individual level, based on costs for pregnancy and cost for the open days. Estrus observation was performed by visual inspection for 20 min periods, twice a day and heifers observed in estrus inseminated (OEAI). Observed in estrus inseminated heifers were 10.5% at first, 26.8% at second and 24.0% at third AI (P >0.05). The global P/AI after first AI was 58.6%; the P/AI after FTAI, 58.0%; and the P/AI after first OEAIs, 64.2%. Pregnancy per AI values were better in the IPD group [55.2% for 5dCO vs. 62.4% for 5dCOP4; odds ratio (OR) 0.35, 95% confidence interval (CI) 0.18-0.70; P=0.003], and a significant effect of the temperature humidity index (THI) on P/AI was observed (P = 0.03). The protocol 5dCOP4 led to a significantly better synchronization rate (85.7% vs. 40.0% for 5dCO; P = 0.01) and a numerically higher P/AI (74.5% vs. 49.0% for 5dCO; P = 0.24) when THI values were ≥ 70. During the cold season, there were no differences between the experimental groups for the synchronization rate (P = 0.9) nor for the P/AI (P = 0.6). The P/AI was 52.2% after the second AI and 60.6% after the third AI. Inseminations per pregnancy and open days did not differ significantly across experimental groups. However, reproduction costs per heifer were 130.8 ± 116.1 and 152.3 ± 129.5€ for 5dCO and 5dCOP4 groups, respectively, for the whole study (P = 0.051) and the average cost per AI was 58.23 ± 27.9 € for 5dCO and 76.3 ± 36.2 € for 5dCOP4 (P < 0.0001). During the cold season, protocols were associated with similar costs to the whole study, but they differed notably during the hot season (194.3 ± 137.6 vs. 177.3 ± 134.2 for 5dCO and 5dCOP4, respectively; P=0.49), reflecting the better reproductive performance with an IPD during the summer (P = 0.003). Advisors and farmers need to consider farm conditions and characteristics (herd management, staff training, and seasonality, among others) to achieve the best economic and reproductive performance in the dairy herds, when implementing hormonal synchronization protocols. Thus, cost-effectiveness depends on seasonality when implementing reproductive strategies with 5 d Co-synch 72h and combined OEAI at a rearing farm. With high THI-values, the inclusion of IPD in hormonal protocols in heifers is recommended, while it is not required during the cool season.

这项随机、对照研究的目的是评估在不同温湿度指数 (THI) 和不使用阴道内孕激素装置 (IPD) 的情况下进行第一次至第三次人工授精 (AI) 的奶牛荷斯坦小母牛的繁殖和经济性能。观察发情后结合AI。来自一个饲养商业农场的总共 503 头小母牛被随机分配到 5d Co-synch 72 h 协议（5dCO；n=261）或 5d Co-synch 协议加 IPD（5dCOP4；n=242）进行第一次 AI。在一部分小母牛 (n = 193) 中，我们确定了孕酮 (p4) 并在第 0、5、8 和 15 天进行了卵巢超声扫描。如果 p4 > 1 ng/mL 和 a存在黄体；如果 p4 < 1 ng/mL，黄体溶解和卵泡 > 在第 8 天同步 观察到直径为 8 毫米；如果 p4 > 1 ng/mL 并且发生排卵，则在第 15 天同步，定义为在第 8 天检测到卵泡的卵巢中存在 CL。在 AI 后第 28-35 天通过超声扫描仪进行妊娠诊断. 在 AI 后第 50-56 天和第 100-113 天通过超声进行诊断确认。未怀孕的小母牛 (n=205) 与第二个固定时间 AI (FTAI) 的相同协议和第三个 FTAI 的 104 重新同步。计算每次 AI 的妊娠率 (P/AI) 和每次 AI 后的流产率。生殖成本是根据怀孕成本和开放日成本在个人层面计算的。发情观察通过目视检查进行，每天两次，每次 20 分钟，并在发情受精 (OEAI) 中观察小母牛。P >0.05）。第一次 AI 后的全球 P/AI 为 58.6%；FTAI后的P/AI，58.0%；第一次 OEAI 后的 P/AI 为 64.2%。IPD 组每个 AI 值的妊娠率更好 [5dCO 为 55.2%，5dCOP4 为 62.4%；优势比 (OR) 0.35，95% 置信区间 (CI) 0.18-0.70；P= 0.003]，观察到温度湿度指数（THI）对 P/AI 的显着影响（P  =0.03）。协议 5dCOP4 导致显着更好的同步率（85.7% 对 5dCO 的 40.0%；P  = 0.01）和数值更高的 P/AI（74.5% 对 5dCO 的 49.0%；P  = 0.24）当 THI 值≥ 70. 在寒冷季节，实验组间同步率无差异（P = 0.9) 也不用于 P/AI ( P  = 0.6)。第二次 AI 后的 P/AI 为 52.2%，第三次 AI 后为 60.6%。每次怀孕和开放日的人工授精在实验组之间没有显着差异。然而，在整个研究中，5dCO 和 5dCOP4 组的每头小母牛繁殖成本分别为 130.8 ± 116.1 和 152.3 ± 129.5 欧元（P  = 0.051），5dCO 和 36.3 欧元的每头 AI 平均成本为 58.23 ± 27.9 欧元。对于 5dCOP4 ( P < 0.0001)。在寒冷季节，协议与整个研究的成本相似，但它们在炎热季节显着不同（5dCO 和 5dCOP4 分别为 194.3 ± 137.6 和 177.3 ± 134.2；P=0.49)，反映了夏季 IPD 的更好繁殖性能 ( P  = 0.003)。在实施激素同步方案时，顾问和农民需要考虑农场条件和特征（牛群管理、员工培训和季节性等），以实现奶牛群的最佳经济和繁殖性能。因此，在养殖场实施 5 d Co-synch 72h 和组合 OEAI 的繁殖策略时，成本效益取决于季节性。由于 THI 值较高，建议将 IPD 纳入小母牛的激素方案中，而在凉爽季节则不需要。