Abstract The aim of the study was to characterize the interrelationship between decreased ruminal fluid pH during subacute ruminal acidosis (SARA) and concentrations of principal constituents of milk and biochemical indices associated with nitrogen utilizations such as rumen ammonia nitrogen (RAN), blood urea nitrogen (BUN) and milk urea nitrogen (MUN). Ruminal fluid samples were obtained by rumenocentesis from 305 cows representing 13 dairy herds. The cows were divided according to ruminal fluid pH into three groups: low, moderate, and high rumen pH cows. The herds were divided into three groups on the basis of the percentages of cows with an assigned value of ruminal fluid pH: SARA-positive, SARA-risk and SARA-negative. SARA-positive herds were characterized by higher concentrations of RAN (12.6 vs. 6.9 mg/dL), BUN (16.2 vs. 10.1 mg/dL) and MUN (12.4 vs. 9.1 mg/dL) compared to SARA-negative herds. Similarly, low-rumen pH cows had greater concentrations of RAN, BUN and MUN than high-rumen pH cows (11.9 vs. 5.8 mg/ dL, 19.9 vs. 14.1 mg/dL, and 12.3 vs. 9.5 mg/dL, respectively). Moreover, SARA-positive herds and low-rumen pH cows had the highest lactose and the lowest fat concentrations in milk. The study demonstrated that the concentration of milk urea nitrogen could be considered one of the indirect and non-invasive indicators of the occurrence of subacute ruminal acidosis in dairy herds.

中文翻译：

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与奶牛亚急性瘤胃酸中毒相关的无创指标

摘要 本研究的目的是表征亚急性瘤胃酸中毒 (SARA) 期间瘤胃液 pH 值降低与牛奶主要成分浓度和与氮利用相关的生化指标如瘤胃氨氮 (RAN)、血尿素氮 ( BUN) 和牛奶尿素氮 (MUN)。通过瘤胃穿刺术从代表 13 个奶牛群的 305 头奶牛获得瘤胃液样本。根据瘤胃液 pH 值将奶牛分为三组：低、中和高瘤胃 pH 值奶牛。根据具有指定瘤胃液 pH 值的奶牛百分比，将牛群分为三组：SARA 阳性、SARA 风险和 SARA 阴性。SARA 阳性畜群的特征在于更高浓度的 RAN（12.6 与 6.9 mg/dL）、BUN（16.2 与 10. 1 mg/dL) 和 MUN（12.4 对 9.1 mg/dL）与 SARA 阴性牛群相比。同样，低瘤胃 pH 值奶牛的 RAN、BUN 和 MUN 浓度高于高瘤胃 pH 值奶牛（分别为 11.9 对 5.8 mg/dL、19.9 对 14.1 mg/dL 和 12.3 对 9.5 mg/dL） . 此外，SARA 阳性牛群和低瘤胃 pH 值奶牛的牛奶中乳糖含量最高，脂肪含量最低。研究表明，牛奶尿素氮浓度可作为奶牛亚急性瘤胃酸中毒发生的间接非侵入性指标之一。SARA 阳性牛群和低瘤胃 pH 值奶牛的牛奶中乳糖含量最高，脂肪含量最低。研究表明，牛奶尿素氮浓度可作为奶牛亚急性瘤胃酸中毒发生的间接非侵入性指标之一。SARA 阳性牛群和低瘤胃 pH 值奶牛的牛奶中乳糖含量最高，脂肪含量最低。研究表明，牛奶尿素氮浓度可作为奶牛亚急性瘤胃酸中毒发生的间接非侵入性指标之一。