Carlsson J, Pehrson B
Experimental Station, Veterinary Institute, Skara, Sweden.
Zentralbl Veterinarmed A. 1993 Apr;40(3):205-12. doi: 10.1111/j.1439-0442.1993.tb00618.x.
The concentration of urea was measured in bulk milk samples taken on seven occasions during a period of 13 months from 1,658-1,815 of the 2,100 suppliers of milk to a dairy. The mean concentration of urea was significantly higher when the cows were grazing than when they were housed, but there were no significant variations within either of these periods. In herds with very low milk urea concentrations while they were housed (< 2.4 mmol/l) the mean increase during the grazing season was approximately 2.0 mmol/l, whereas in herds with very high urea concentrations while they were housed (> 6.0 mmol/l) there was a slight decrease in urea concentration during the grazing season. The annual milk yield of herds with low urea concentrations was significantly lower than the yield of herds with intermediate or high concentrations. The interval between calving and first insemination was significantly longer in herds with low milk urea concentrations, but these herds also had a higher 56-day non-return rate.
在13个月的时间里，从向一家乳制品厂供应牛奶的2100家供应商中选取了1658 - 1815家，在七个不同时间采集了散装牛奶样本，并测定了尿素浓度。奶牛放牧时尿素的平均浓度显著高于圈养时，但在这两个时期内均无显著变化。在圈养时牛奶尿素浓度很低（< 2.4 mmol/l）的牛群中，放牧季节的平均增加量约为2.0 mmol/l，而在圈养时尿素浓度很高（> 6.0 mmol/l）的牛群中，放牧季节尿素浓度略有下降。尿素浓度低的牛群的年牛奶产量显著低于尿素浓度中等或高的牛群。牛奶尿素浓度低的牛群中，产犊与首次输精之间的间隔明显更长，但这些牛群的56天不返情率也更高。
