EN
Magnesium (Mg) is an activator of more than three hundred enzymes and a cofactor in synthesis and release of hormones. Currently, magnesium deficiency occurs in dairy cows most frequently in subclinical form, with symptoms limited to decreased appetite and decreased milk yield. The study covered 75 cows: 50 cows, which were diagnosed with magnesium deficiency in the antenatal period. The control group consisted of 25 healthy cows. In group I (n = 25) increased supplementation was not applied; in group II (n = 25) the intake of Mg was increased, using a 7% magnesium supplement. Blood samples for tests were taken 2 weeks prepartum and 1 and 2 weeks postnatally, indicating the concentration of: total magnesium (Mg), total calcium (Ca), inorganic phosphorus (Pi), copper (Cu), zinc (Zn), total bilirubin (tB), total protein (TP), glucose (Glu) and cholesterol (TC) as well as the activity of aspartate aminotransferase (AST) and gamma-glutamyl transpeptidase (GGTP). In group 1, the highest number of cows with decreased appetite and postpartum weakness was identified, which exhibited the lowest increase rate of milk production and significantly lower mean blood calcium concentration. The highest mean concentrations of tB and the decrease in TC and Glu concentrations were also recorded in this group. Our own studies confirm the need to monitor mineral deficiencies not only during lactation but also before delivery, as well as the effectiveness of appropriate prophylactic regimen, based on oral administration of magnesium preparations which cause the slightest biochemical changes in blood. Lack of supplementation in the subclinical form of antenatal Mg deficiency may cause severe gastrointestinal and reproductive disorders in the postnatal period.