Farmers have been feeding increasing amounts of protein in the last few years. However, excess amounts lead to increased blood urea levels and lower plasma progesterone concentrations. In turn, lower plasma progesterone concentrations during the first five days after insemination could be one of the reasons for lower survival rates among early embryos and reduced pregnancy rates. Both urea and progesterone concentrations are measured in blood samples, but they can be measured more cheaply and easily in milk.

Click HERE for a milk urea nitrogen calculator.