The main objective of the current study was to measure the effect of incomplete milking on luteal activity and on pregnancy hazard. We also aimed to study the effect of early-lactation hyperketonemia (i.e., β-hydroxybutyrate blood concentration ≥1.4 mmol/L during the first 3 wk in milk) on those reproductive outcomes. Multiparous Holstein cows (n = 853) from 13 commercial herds were enrolled in a randomized controlled trial. Cows were assigned to a control or a treatment group, incompletely milked (10–14 L of milk collected/d) from 1 to 5 DIM. Blood samples were collected once a week during weeks in milk 1 to 3 for β-hydroxybutyrate blood concentration, and a threshold of 1.4 mmol/L was used to define hyperketonemia. During weeks in milk 5 and 7, cows were sampled for progesterone blood concentration, and a threshold of 1 ng/mL was used to define luteal activity. Reproductive information and culling dates were obtained through herd records. Logistic regression models and survival analyses were used to assess the effect of treatment on luteal activity and on pregnancy hazard, respectively. Analogous models were used to investigate the effect of early-lactation hyperketonemia on reproductive outcomes. The odds of luteal activity for incompletely milked cows were 1.1 (95% confidence interval: 0.72–1.7) times those of conventionally milked cows. The effect of treatment on pregnancy hazard varied as a function of time, parity, and start of the breeding period. In second-parity cows that started the breeding period <55 d in milk, the pregnancy hazard (95% confidence interval) in incompletely milked cows was 576.3 (240.0–1,383.7), 36.9 (18.9–72.1), 6.8 (3.3–13.8), 2.5 (1.0–5.9), and 0.13 (0.07–0.26) times that of conventionally milked cows at 1 to 21, 22 to 43, 44 to 65, 66 to 87, and >87 d after the voluntary waiting period, respectively. The treatment did not have an effect on pregnancy hazard in cows in third parity or greater or in those starting the breeding period ≥55 d in milk. Early-lactation hyperketonemia was not associated with any of the reproductive outcomes. In conclusion, the incomplete milking protocol had no effect on luteal activity and had a positive effect on pregnancy hazard in second-parity cows in herds with a short voluntary waiting period (<55 d). We did not observe an effect of early-lactation hyperketonemia on luteal activity or on pregnancy hazard.

本研究的主要目的是测量不完全挤奶对黄体的影响活动和对怀孕的危害。我们还旨在研究早期泌乳性高血钾症（即牛奶中前3周内β-羟丁酸血药浓度≥1.4mmol / L）对这些生殖结局的影响。来自13个商业牛群的多头荷斯坦奶牛（n = 853）被纳入一项随机对照试验。母牛被分配为对照组或治疗组，从1到5 DIM不完全挤奶（每天收集10–14 L牛奶）。每周在每周1至3的牛奶中每周收集一次血液样品中的β-羟基丁酸血药浓度，并使用1.4 mmol / L的阈值定义高酮血症。在5号和7号乳汁中的几周内，对母牛的孕酮血样进行采样，并使用1 ng / mL的阈值定义黄体活性。生殖信息和通过畜群记录获得淘汰日期。使用逻辑回归模型和生存分析分别评估治疗对黄体活动和妊娠危险的影响。使用类似的模型来研究早期泌乳性高血钾症对生殖结局的影响。不完全挤奶的母牛黄体活动的几率是传统挤奶的母牛的1.1倍（95％置信区间：0.72-1.7）。治疗对怀孕危害的影响随时间，胎次和育种期的开始而变化。在开始育种期<55 d的第二胎母牛中，不完全挤奶的母牛的妊娠危险（95％置信区间）为576.3（240.0–1,383.7），36.9（18.9–72.1），6.8（3.3–13.8） ，2.5（1.0-5.9）和0.13（0.07-0。26）分别是自愿等待期后1到21、22到43、44到65、66到87和> 87 d的常规奶牛的两倍。该处理对第三胎或以上胎的母牛或在开始繁殖期≥55d的母牛的妊娠危险没有影响。早期泌乳性高酮血症与任何生殖结局均无关。总而言之，不完全挤奶方案对黄皮活动没有影响，对自愿等待期短（<55 d）的第二胎母牛的妊娠危害有积极影响。我们没有观察到早期泌乳性高血钾对黄体活动或妊娠危险的影响。该处理对第三胎或以上胎的母牛或在开始繁殖期≥55d的母牛的妊娠危险没有影响。早期泌乳性高酮血症与任何生殖结局均无关。总而言之，不完全挤奶方案对黄皮活动没有影响，对自愿等待期短（<55 d）的第二胎母牛的妊娠危害有积极影响。我们没有观察到早期泌乳性高血钾对黄体活动或妊娠危险的影响。该处理对第三胎或以上胎的母牛或在开始繁殖期≥55d的母牛的妊娠危险没有影响。早期泌乳性高酮血症与任何生殖结局均无关。总而言之，不完全挤奶方案对黄皮活动没有影响，对自愿等待期短（<55 d）的第二胎母牛的妊娠危害有积极影响。我们没有观察到早期泌乳性高血钾对黄体活动或妊娠危险的影响。不完整的挤奶规程对黄体活动没有影响，对自愿等待时间短（<55 d）的第二胎母牛的妊娠危害有积极影响。我们没有观察到早期泌乳性高血钾对黄体活动或妊娠危险的影响。不完整的挤奶规程对黄体活动没有影响，对自愿等待时间短（<55 d）的第二胎母牛的妊娠危害有积极影响。我们没有观察到早期泌乳性高血钾对黄体活动或妊娠危险的影响。