Lower Milk Urea Research Articles

The relationships between seasonal variations in the concentration of urea in bulk milk and the production and fertility of dairy herds.

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.

The effect of additional feeding on the fertility of high-yielding dairy cows.

One hundred and ninety three pairs of cows were selected from 38 herds, and the numbers of each pair were assigned at random to experimental and control groups. Each control cow was fed according to its yield with the feedstuffs normally used by the herd. Each experimental cow was fed in the same way and, in addition, received 500 g of a feed additive twice daily from the 40th day of lactation until first insemination or to the 75th day of lactation if no visible oestrus had been observed between days 40 and 75. One kg of the feed additive contained glucogenic substances (glycerol and Ca-propionate) equivalent to 1.90 moles of glucose, 13.6 MJ metabolizable energy, and 180 g digestible crude protein. There were no significant differences between the groups with respect to their mean daily milk yield, their plasma glucose concentrations at first insemination, or the interval between calving and first insemination. However, the experimental cows had a significantly shorter interval between calving and last insemination (mean difference 11.0 days). The pregnancy rate was significantly higher among cows with high than among cows with low plasma glucose concentrations. There was also a tendency towards a reduced pregnancy rate among cows with either high (greater than 7.0 mmol/litre) or low (less than 4.0 mmol/litre) milk urea concentrations.