[The usefulness of determining urea levels and the acidity of milk for evaluating protein nutrition in cows].

Samples of blood, urine and milk were examined in 94 clinically healthy cows of 10 herds. The average milk samples and the feed ration used in these herds were also examined. The determination of urea concentration and milk acidity was evaluated as to its suitability for the assessment of the protein-glycide ratio and acid-base activity of feed ration. The determination of urea content in an average milk sample was found to be an expeditious procedure. The results of this examination can be used for the evaluation of the protein supply to cows with the same reliability as the determination of serum urea. The passage of urea from serum to milk was proportional. The correlation coefficient for the relation of both parameters was statistically highly significant (r = 0.940). According to the calculated equation of regression line (f2 = 0.734 + 0.669 X f1), the values from 2.94 to 4.10 mmol/l are approximately adequate to the reference range of serum urea from 3.30 to 5.00 mmol/l in milk used in Czechoslovakia. The acidity of milk was found to have a low sensitivity for being used with success for the determination of the acid-base activity of feed ration. The examination of the net acid-base urinary output cannot be replaced by the determination of milk acidity.