evaluation of the monthly and seasonal correlations between milk protein and urea concentrations in dairy holstein cows in oromiah region

monthly and seasonal concentrations of milk protein and urea and their relationships were investigated in 614 milk samples from 61 industrial holstein dairy herds in urmia, iran. milk samples were prepared monthly interval up to 12 months. the amount of 10 ml milk was prepared from each dairy herd when they were delivering to the milk factory. milk protein and urea concentration was evaluated by titration and spectrophotometer methods, respectively using commercial kits after separation of the milk casein. results were analyzed by anova and correlation tests. the overall mean for milk urea and protein was 14.77 mg/dl and 3.15%, respectively. the lowest concentrations of milk urea and protein was found in may (7.13 mg/dl) and april (3.1%) and the highest in september (26.3 mg/dl) and march (3.22%), respectively. the range for milk urea concentration was from 0.01 to 49.8 mg/dl and for protein between 2.18 to 3.94%, respectively. the lowest concentrations of milk urea and protein were observed in winter (10.9 mg/dl, 3.11%) and the highest was in summer (20.9 mg/dl) and autumn (3.19%), respectively. anova showed significant monthly and seasonal differences for milk urea and protein concentrations (p<0.01). the lowest 95% confidence interval for milk urea was found in april (2.69 mg/dl) and the highest in september (29.6 mg/dl). for the milk protein the lowest 95% confidence interval was observed in september (3.06%) and the highest in december (3.2%).the results of the monthly and seasonal correlations between milk urea and protein concentrations showed no differences except for february (r=-0.35, p<0.05). it is concluded that there is a concentration of urea exists in cow’s milk in that it is different between months and seasons. the lack of correlations between parameters in cow’s milk indicates that they are independent parameters and not correlated to each other.