The experiment was conducted on 30 periparturient Polish Holstein-Friesian Black-and-White cows. Animals were kept in a loose-housing system and received TMR (total mixed ration) whose qualitative and quantitative composition varied with the stage of lactation and milk yield. Blood for biochemical analyses was collected by a veterinarian three times: 1-3 weeks prepartum (I), 1-3 weeks postpartum (II), and 4-8 weeks postpartum. Blood samples were analysed for energy metabolism (glucose concentration), protein metabolism (total protein and albumins), liver status (aspartate aminotransferase and alanine aminotransferase) lipid metabolism (cholesterol and triglycerides), and minerals (calcium, magnesium, phosphorus). The parameters were stable and generally within the physiologically normal range, except protein which in lactations 2-3 and 4 slightly exceeded the reference value at the third blood sampling. The reference values were also exceeded for albumins in lactations 1, 2-3 and 4 at the third blood sampling. Differences (p≤0.01) were observed only in the cholesterol content at the peak of lactation between the first and fourth lactation. The cows yielding more than 9,700 kg milk were characterized by higher blood glucose levels, but lower protein levels compared to the cows producing less than 9,700 kg milk. At the peak of lactation, the protein level exceeded normal values regardless of the milk production level. In our study, peak lactation cows with lower milk yield showed a higher level of AST, which exceeded normal values. In our study, the lipid indicators (cholesterol and triglycerides) were within the physiologically normal range. The highest cholesterol level was observed during the dry period in the blood of lower yielding cows. All blood parameters were stable and fell within the physiologically normal range except for protein, which slightly exceeded the reference value at the third sampling.  

24.4.2019