Sources of variation in milk urea nitrogen in Ohio dairy herds
Sources of variation in milk urea nitrogen in Ohio dairy herds
复制标题
DOI：
10.3168/jds.s0022-0302(03)73751-5
复制
发表时间：
2003-05-01
影响因子：
3.5
通讯作者：
Saville, WJA
中科院分区：
文献类型：
--
作者：
Rajala-Schultz, PJ;Saville, WJA
这项研究的目的是估计可归因于测试日、奶牛个体和牛群效应的牛奶尿素氮(MUN)浓度的变异量，并描述与俄亥俄州奶牛群MUN测量相关的因素。数据来自24个荷斯坦牛群，其中一半被归类为低产(LP)[滚动牛群平均产奶量(RHA)7,258公斤]，另一半被归类为高产(HP)牛群(RHA产量和GT；10,433公斤)。从奶牛每月测试日的牛奶样本中测量MUN浓度。利用MLwiN中的多水平建模技术，分别对LP和HP牛群进行分析，未调整的平均MUN分别为13.9 mg/dl和11.3 mg/dl。两组间的方差结构不同。在LP群体中，大多数变异性在测试日水平上被发现，而在HP群体中，在群体水平上被发现。两组的MUN均在哺乳期第1个月最低，且季节与MUN相关。在HP牛群中，试验日产奶量、乳脂率和SCC与MUN相关。在模型中有显著解释变量的情况下，两组在群体水平上解释的差异比例较大，而在测试日水平上解释的差异较小。HP群体中测试日之间的MUN变异性较低可能表明群内的日常喂养和管理更一致。在解释MUN时，应考虑到测试日期之间的巨大变异性，并应在一天中的同一时间采集样本，以将日常变异性降至最低。
The purpose of this study was to estimate the amount of variation in milk urea nitrogen (MUN) concentrations attributable to test-day, individual cow, and herd effects and to describe factors associated with MUN measurements in Ohio dairy herds. The data came from 24 Holstein herds, half of which were classified as low producing (LP) [rolling herd average (RHA) milk production < 7,258 kg] and half as high producing (HP) herds (RHA production > 10,433 kg). MUN concentration was measured from cow's monthly test-day milk samples. The data were analyzed using multilevel modeling technique in MLwiN, separately for LP and HP herds.The unadjusted mean MUN was 13.9 mg/dl for the HP herds and 11.3 mg/dl for the LP herds. The variance structure was different between the two groups. Most of the variability was found at test-day level in the LP herds, but at herd level in HP herds. MUN was lowest during the first month of lactation, and also season was associated with MUN in both groups. Test-day milk yield, milk fat percentage, and SCC were associated with MUN in the HP herds. With significant explanatory variables in the model, proportionally more of the variation was explained at herd level and less at test day level in both groups.Lower variability in MUN between test days in the HP herds may indicate more consistent day-to-day feeding and management within a herd. The great variability between test days should be considered when interpreting MUN and samples should be collected at the same time of the day to minimize day-to-day variability.