Butler W R, Calaman J J, Beam S W
Department of Animal Science, Cornell University, Ithaca, NY 14853, USA.
J Anim Sci. 1996 Apr;74(4):858-65. doi: 10.2527/1996.744858x.
The objectives of this study were to relate concentrations of plasma (PUN) and milk (MUN) urea nitrogen to pregnancy rate in dairy cows and compare various methods of analysis and preparation of milk for measuring MUN. In two experiments, blood or milk samples were collected on the day of AI from Holstein cows (n = 160 and n = 155, respectively). Three methods of MUN analysis were compared. Two laboratory chemical procedures yielded similar results, whereas a quick dipstick method overestimated chemical analyses. Before and after milking strip samples had MUN concentrations equivalent to those in composite milk. Concentrations of PUN or MUN greater than 19 mg/dL were associated with decreased (P < .02) pregnancy rates (18 and 21 percentage point reduction in the two experiments). In two subset groups of cows (n = 51 and n = 23, respectively), plasma progesterone or MUN concentrations were monitored during the 5-d period after AI. Plasma progesterone concentrations increased similarly during the period for cows divided into low vs high PUN but were greater in pregnant than in nonpregnant cows on d 4 and 5 (P < .04). The MUN concentrations showed low within-cow variation (CV = 8%) but were lower in pregnant cows and had a decreasing trend over time compared with nonpregnant cows (P < .05). Based on this study, plasma and milk will yield similar results for monitoring urea nitrogen in dairy cows; PUN and MUN concentrations > 19 mg/dL were associated with approximately a 20 percentage point decrease in pregnancy rate after AI in lactating dairy cattle.
本研究的目的是将奶牛血浆尿素氮（PUN）和牛奶尿素氮（MUN）的浓度与妊娠率相关联，并比较测量MUN的各种牛奶分析和制备方法。在两项实验中，于人工授精当天从荷斯坦奶牛采集血样或奶样（分别为n = 160头和n = 155头）。比较了三种MUN分析方法。两种实验室化学程序得出了相似的结果，而快速试纸法高估了化学分析结果。挤奶前后的条带样品的MUN浓度与混合奶中的浓度相当。PUN或MUN浓度大于19 mg/dL与妊娠率降低（P < 0.02）相关（两项实验中分别降低了18和21个百分点）。在两组奶牛亚群（分别为n = 51头和n = 头）中，在人工授精后的5天内监测血浆孕酮或MUN浓度。对于分为低PUN组和高PUN组的奶牛，血浆孕酮浓度在该时间段内的升高情况相似，但在第4天和第5天，怀孕奶牛的血浆孕酮浓度高于未怀孕奶牛（P < 0.04）。MUN浓度在奶牛个体内的变异较低（CV = 8%），但怀孕奶牛的MUN浓度较低，且与未怀孕奶牛相比随时间呈下降趋势（P < 0.05）。基于本研究，血浆和牛奶在监测奶牛尿素氮方面将产生相似的结果；PUN和MUN浓度> 19 mg/dL与泌乳奶牛人工授精后妊娠率降低约20个百分点相关。
