Milk urea nitrogen (MUN) has been introduced as a means to estimate urinary nitrogen (N) excretion and protein status of dairy cattle. For Holstein cows, the amount of urinary N excreted (g/d) was originally reported to be 12.54 x MUN (mg/dl), but recently urinary N (g/d) was reported to equal 17.64 x MUN (mg/dl). The objectives of the present study were to evaluate models to predict urinary N and expected MUN, by using older and newer data sets, and to quantify changes that may have occurred in MUN measurements over time. Two data sets were used for model evaluation. Data set 1 was from the spring of 1998 and data set 2 was from the spring of 1999. Similar cows and diets were used in both studies. By using data set 1, the newer model underestimated MUN by an average of 3.8 mg/dl, whereas the older model was accurate. By using data set 2, the older model overestimated MUN by 4.8 mg/ dl, but the newer model was accurate. In the period between the two studies, the MUN measured appeared to decrease by an average of 4.0 mg/dl. By using current wet chemistry methods to analyze for MUN, urinary N (mg/dl) can be predicted as 0.026 x MUN (mg/dl) x body weight (kg). Because of changes in methodology that occurred in the fall of 1998, target MUN concentrations have decreased to 8.5 to 11.5 mg/dl for most dairy herds compared with previous target concentrations of 12 to 16 mg/dl.
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机译:牛奶尿素氮 (MUN) 已被引入作为估计奶牛尿氮 (N) 排泄和蛋白质状况的一种手段。对于荷斯坦奶牛,最初报告的尿氮排泄量 (g/d) 为 12.54 x MUN (mg/dl),但最近报告的尿氮 (g/d) 等于 17.64 x MUN (mg/dl)。本研究的目的是通过使用较旧和新的数据集来评估预测尿氮和预期 MUN 的模型,并量化 MUN 测量中可能随时间发生的变化。使用两个数据集进行模型评估。数据集1是1998年春季的数据,数据集2是1999年春天的数据。两项研究都使用了类似的奶牛和日粮。通过使用数据集 1,新模型平均低估了 3.8 mg/dl,而旧模型是准确的。通过使用数据集 2,旧模型高估了 4.8 mg/dl,但新模型是准确的。在两项研究之间的期间,测得的模拟联合国似乎平均下降了4.0毫克/分升。通过使用当前的湿化学方法分析 MUN,尿氮 (mg/dl) 可以预测为 0.026 x MUN (mg/dl) x 体重 (kg)。由于1998年秋季方法发生了变化,大多数奶牛群的目标模拟联合国浓度已降至8.5至11.5毫克/分升,而以前的目标浓度为12至16毫克/分升。
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