[Urea content in the blood serum and fertility in cows]

The interrelation between dietary protein, total protein level and blood serum urea, and conception rate in cows has been studied in the course of two four-month periods on two dairy farms with a total of 150 test cows that were fed on varying rations. It has been demonstrated that the level of serum urea corresponded to the amount of protein in the diet (in percent of dry matter) and could be used in meeting the protein requirements of cows. The content of total protein has not proved to be a suitable index for the same purpose. A weak or moderate negative correlation (from r=-0.07 to r=0.43) has been found to exist between the amount of total protein and that of urea in the serum. The correlation method of Orlov - Dounyov has been used to determine the interrelation between the level of total protein and urea in the blood serum, on the one hand, and the total conception, the conception rate at first insemination, and the cases of anaphrodisia, on the other. It has been found that cows with urea levels closer to the Blowey values (optimal level of 25 mg%) show higher conception rate. The high content of protein in the rations, resp. of urea in the blood serum is an important factor in the etiology of anaphrodisia in cows. No such correlation has been established with regard to total protein.