evaluatIon of Selected bIochemIcal P arameterS In blood PlaSma, urIne and mIlk of daIry cowS durIng the lactatIon PerIod

The aim of our study was to determine selected biochemical parameters in the blood, urine and milk of dairy cows. Fifteen dairy cows from selected agricultural farms were divided into three groups as follow: group i- 3-4 weeks after calving (the beginning of lactation), group ii - 3-4 months after calving (the middle of lactation), and group iii - 2-3 weeks before calving (the dry period). Concentrations of selected biochemical parameters in the blood (aspartate aminotransferase – AST, urea, total proteins - Tp , glucose, and cholesterol), urine (calcium - Ca, phosphorus p, urea and pH), and milk (fats, proteins, lactose, solids, Somatic Cell Count, urea, milk freezing point and rennetability) were measured. Glucose concentration (3.22±0.21 mmol.l -1 ) was significantly lower at the beginning of lactation (p<0.05) in comparison with the middle of lactation (3.69±0.08 mmol.l -1 ) and the dry period (3.74±0.21 mmol.l -1 ). However, concentration of AST (1.42±0.31μkat.l -1 ) was significantly higher (p<0.01) at the beginning of lactation than in the dry period (0.88±0.31 μkat.l -1 ). Concentration of cholesterol (6.22±0.76 mmol.l -1 ) in the middle of lactation was significantly higher (p<0.001) than those at the beginning of lactation (3.82±0.67 mmol.l -1 ) and dry period (2.842±0.67 mmol. l -1 ). Cows in the middle of lactation had a higher freezing point of milk (526.20±1.92 -m.°C) (p<0.01) in comparison with dairy cows at the beginning of lactation (520.00±2.74-m°C). Some other symptoms leading to sub-clinical diseases, besides worsening the technological quality of the cow milk, were found.