BONE METABOLISM MARKERS AND BLOOD MINERALS CONCENTRATION IN DAIRY CATTLE DURING PREGNANCY AND LACTATION

Biochemical markers of bone metabolism are substances in blood and urine that indicate how intensively bone is forming or degrading at the time of sample (blood or urine) collection. The aim of the study was to establish concentration of total calcium (Ca), inorganic phosphate (iP), magnesium (Mg), C-terminal telopeptide crosslinks of collagen I (CTx) (biochemical marker of bone resorption) and activity of total alkaline phosphatase (ALP) and bone specific alkaline phosphatase (BALP) (biochemical marker of bone formation) in blood serum of clinically healthy mature dairy cows from dry period until peak lactation. Holstein-Friesian cows (n=54) with high milk yields (average 8,463 kg/previous lactation) were enrolled in the study. Cows were divided in 5 groups according to stage of lactation: 1. approximately 1 month before calving (AP) (early dry period) (n=10), 2. 10 to 1 day AP (close-up dry period) (n=10), 3. 0-48 hours after calving (PP) (n=10), 4. 10-20 days PP (n=10) and 5. peak of lactation (35-55 days in milk) (n=14). The nadir of mean Ca and iP were in the third group and significantly lower than in other groups (P<0.05). Mean Mg was higher in groups 3 and 5 compared to groups 2 and 4 (P<0.05). The lowest mean value of BALP was established in group 1. The difference was statistically significant compared to all other groups. The highest values of CTx were measured in groups 4 and 5. These values were also significantly higher compared to groups 1, 2 and 3. The lowest CTx values were measured in the 1. group. Results of the study indicate that bone tissue is the most catabolically active 10 to 20 days after calving and the most anabolically active during the dry period. Strong negative correlation (P<0.01) was established between BALP and minerals Ca and iP.