ABSTRACT
Monthly variation of magnesium [Mg] concentration in milk serum was investigated in industrial and semi-industrial dairy herds of Urmia, northeastern Iran, in 2002-3. Total number of 1, 112 milk samples from 96 herds including 615 samples from 53 industrial herds and 497 samples from 43 semi-industrial dairy herds were examined. 10-ml milk samples were collected monthly up to 12 months from each herd in the milk factory. Milk fat was separated by centrifugation. Milk serum was then separated after casein was precipitated by 0.1 N HC1. Spectrophotometery was used to measure the milk Mg concentration, using Mg kit [Ziest Chimi, Iran]. The overall mean +/- SD of Mg concentration in milk serum in industrial and semi-industrial herds was 5.47 +/- 1.15 and 5.35 +/- 1.21 mmol/l, respectively. The differences in Mg concentration between breeding systems were significant [P<0.05]. The highest monthly mean Mg concentration in industrial and semi-industrial dairy herds was 6.39 and 6.05 and the lowest mean was 4.29 and 4.02 mmol/l, respectively. The lowest monthly mean Mg concentration in industrial and semi-industrial dairy milk herds was observed in August; the highest in November. The concentration decreased from March to August and then increased gradually up to November. The mean Mg concentration in milk serum within industrial, semi-industrial herds and between two breeds had a significant [P<0.001] monthly variation-mainly in August and November [P<0.05]. The lowest and highest mean seasonal milk Mg concentration in industrial [4.61, 5.83 mmol/l] and semi-industrial herds [4.53, 5.72 mmol/l] were observed in summer and winter. The mean Mg concentration in milk serum had a significant [P<0.05] seasonal variation-between summer and other seasons. Thus, it could be concluded that milk Mg concentration in industrial herds was higher than semi-industrial dairy herds. The lowest milk Mg concentration was observed in August that could be important to supplement magnesium in food of dairy herds in Urmia