Ryder J, Smith R F, Neary J M
Garston Veterinary Group, Garston House, Portway, Frome, BA11 1PZ, UK.
Department of Livestock and One Health, Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Neston, CH64 7TE, UK.
J Dairy Sci. 2023 Nov;106(11):8087-8097. doi: 10.3168/jds.2023-23253. Epub 2023 Aug 9.
The objectives of this observational cohort study were to assess the effect of body condition score change, back fat depth change, and muscle diameter change on the time to commencement of luteal activity and first estrus in commercial pedigree Holstein cows. A total of 140 of 200 commercial pedigree Holstein cows were enrolled in one dairy herd in Somerset, UK, over 52 wk in 2021 to 2022. The herd used 4 automatic milking machines with in-line progesterone measurement capability to determine commencement of luteal activity and time to first estrus. Cows were followed until at least 60 d postpartum, and milk progesterone was measured daily starting from 10 DIM. Body condition scoring and ultrasound measurements of back fat depth and longissimus dorsi muscle diameter were performed on cows twice, within 7 d of both calving and 60 DIM. Other explanatory variables assessed included parity, 60-d and 305-d milk yield, and subclinical ketosis (β-hydroxybutryate ≥1.2 mmol/L). Occurrence of clinical disease <60 DIM was forced into all models as a binary variable. Data were analyzed using multivariable Cox proportionate survival analyses. Muscle loss was associated with commencement of luteal activity and time to first estrus. A reduction in muscle diameter by 1.5 to 5 mm was associated with the shortest time to the start of luteal activity and first estrus. A reduction in muscle diameter >8 mm was associated with the longest times to luteal activity and first estrus. In addition to being affected by muscle loss, commencement of luteal activity was delayed by subclinical ketosis, clinical disease, and failure to gain body condition to 60 DIM. Cows that had a BCS loss of 0.25 or more between calving and 60 DIM were at least 52 ± 22% less likely to have commenced luteal activity compared with those that gained BCS. Interestingly, cows that had no change in body condition score commenced luteal activity later than those that gained body condition score. Muscle loss was associated with time to first estrus irrespective of clinical disease status. Cows that lost >8 mm of muscle diameter showed estrus behavior later than cows that lost 1.5 to 5 mm. In conclusion, our findings indicate that extensive muscle loss postpartum was associated with a delayed start to luteal activity and first estrus, irrespective of body condition change, clinical disease, and subclinical ketosis. Marginal muscle loss and a gain in body condition, however, were associated with an earlier start to luteal activity and first estrus.
这项观察性队列研究的目的是评估体况评分变化、背膘厚度变化和肌肉直径变化对商业化纯种荷斯坦奶牛黄体活动开始时间和首次发情时间的影响。2021年至2022年的52周内，英国萨默塞特郡的一个奶牛场中，200头商业化纯种荷斯坦奶牛中有140头被纳入研究。该牛场使用4台具有在线孕酮测量功能的自动挤奶机来确定黄体活动开始时间和首次发情时间。对奶牛进行跟踪，直至产后至少60天，并从产后第10天开始每天测量牛奶中的孕酮。在产犊后7天内和产后60天对奶牛进行两次体况评分以及背膘厚度和背最长肌直径的超声测量。评估的其他解释变量包括胎次、60天和305天产奶量以及亚临床酮病（β-羟基丁酸≥1.2 mmol/L）。将产后60天内临床疾病的发生情况作为二元变量强制纳入所有模型。使用多变量Cox比例生存分析对数据进行分析。肌肉损失与黄体活动开始时间和首次发情时间相关。肌肉直径减少1.5至5毫米与黄体活动开始和首次发情的最短时间相关。肌肉直径减少超过8毫米与黄体活动和首次发情的最长时间相关。除了受肌肉损失影响外，亚临床酮病、临床疾病以及未能在产后60天时增加体况都会延迟黄体活动的开始。在产犊至产后60天期间体况评分下降0.25或更多的奶牛与体况评分增加的奶牛相比，开始黄体活动的可能性至少低52±22%。有趣的是，体况评分没有变化的奶牛比体况评分增加的奶牛开始黄体活动的时间更晚。无论临床疾病状态如何，肌肉损失都与首次发情时间相关。肌肉直径减少超过8毫米的奶牛比肌肉直径减少1.5至5毫米的奶牛发情行为出现得更晚。总之，我们的研究结果表明，产后广泛的肌肉损失与黄体活动和首次发情开始延迟相关，而与体况变化、临床疾病和亚临床酮病无关。然而，轻微的肌肉损失和体况增加与黄体活动和首次发情的较早开始相关。
