diurnal variations in milk macro-mineral concentrations in holstein dairy cows in urmia, iran

milk samples from high and low milk producer holstein cows, were obtained during the morning and afternoon milking over a one week period. overall, 1064 samples were tested within 14 times sampling in urmia, iran. milk macro-mineral concentrations in the morning milking and in low producers were greater than in the afternoon and in high producers. the highest and lowest concentrations were observed in na+ and mg++, respectively. mean milk values between low and high producers in the morning, afternoon and daily milking times were different (p < 0.05). the individual comparison of milk parameters between both groups in the different milking times were also different (p < 0.05). the results of correlation among macro-minerals in the morning, afternoon and overall milking showed significant and positive correlations among all macro-minerals except for na+ and k+, in which there was a significant negative correlation (p < 0.05). the highest and lowest correlations were found between ca++ and inorganic phosphorus (ip) (r=0.37, p < 0.05) and na+ and ip (r=0.10, p < 0.05), respectively. it is concluded that the concentration of macro-minerals in different producers varied between milking times. the sodium concentration was the highest while mg++ was the lowest among macro-minerals. the correlation between ca++/ ip was the highest, while na+/k+ revealed a negative correlation. therefore, by organizing the appropriate macro-minerals in the ration, it would be possible to achieve an optimal purpose from animal husbandry.