Seasonal chnages of blood parameters and milk quality in Simmental cows from small holder dairy farm in Croatia

The aim of our study was to improve the milk production at the small-holder dairy farms in order to enhance the quality of the milk produced and to keep the animals healthy. We have introduced the quality milk and blood profile testing for the assessment of nutritional and metabolic status of cows. The blood and milk samples were collected from mid-lactating cows (70-150 DIM) with average milk production of 5800 L per cow a year at fife consecutive periods (1- spring ; 2-summer ; 3-autumn ; 4 -winter 1 ; 5-winter 2) with minimum of 7 cows per group tested. Blood profile consisted of 11 parameters. Milk composition (protein, fat, solids non fat, lactose), somatic cell count with additional superoxide dismutase (SOD) and thiobarbituric acid reactive substances (TBARS) concentration were monthly controlled. Milk protein, solids non fat (SNF) and milk fat changed over the research periods with significantly lower values measured in summer (3, 19 %, p < 0, 01 ; 8, 69%, p < 0, 05) with average of 3, 86% of milk fat, and the highest values were observed in autumn (3, 78% for proteins and 9, 15% for SNF) with significantly higher milk fat content of 5, 57 % (p < 0, 05). The SOD activity in milk was the lowest in autumn (223, 63 U/g prot.) and the highest in summer (429, 9763 U/g prot.) period, and the TBARS concentration was the highest in spring (253, 05 nmol/g prot.) and the lowest in winter (112, 49 nmol/g prot.). The concentration of blood parameters also changed significantly at some stage of the research. In the winter periods significantly higher concentration of urea, total cholesterol, albumin, and minerals calcium and phosphorus were measured (5, 21 mmol/L ; 5, 85 mmol/L, 40, 7g/L ; 2, 47mmol/L ; 2, 05 mmol/L) with the average the lowest values detected in spring. The significantly higher activity of enzyme gluthathion peroxidase (GPx) was also noted in autumn and winter periods (10858, 70 and 24085, 22 U/L ; p< 0, 001). The concentration of betahydroxibutirate (BHB) was significantly higher in the summer (0, 88 mmol/L) with the concurrent significantly lower phosphorus and urea concentration in blood (1, 65 mmol/L and 2, 12 mmol/L). The assessment of blood and milk parameters pointed to seasonal variations of the milk protein and milk fat, and physiology variations of blood parameters for the particular breed of dairy cows. The reason for the significant seasonal difference between the blood and milk parameters was attributed to imbalanced diet, particularly in summer. The results of our study promoted the preparation of the balanced diet for the following productive period at the farm.