## 2 Materials and Methods  
The experimental materials comprised 380 milk samples collected from 38 Black-and-White PHF cows. The cows were in their first lactation (18 animals) and in their second, third and fourth lactation (20 animals). Milk samples were collected at two-week intervals, from the first week postpartum to the fifth month of lactation. Udder health was evaluated based on SCC, in thousands of cells per mL of milk: \(\leq\) 200--healthy udder, 201-400--risk of mastitis (due to a low number of samples in the 400-500 group, these samples were included in the 500-1000 group), 401-1000--subclinical mastitis, \(>\)1000--clinical mastitis [12].  
The cows were kept on a farm located in the Region of Warmia and Mazury (NE Poland). They were housed in free-stall barns. To eliminate the effect of the calving season on milk composition, cows with similar expected calving dates were selected for the experiment. A total mixed ration (TMR) was fed year-round. The TMR was composed of maize silage and haylage, supplemented with farm-made concentrates (protein concentrates, vitamin-mineral premixes) and feed additives that improve productivity and help balance complete diets (protein, rumen-protected fat, active yeast cultures and other energy supplements).  
Samples of fresh milk were analyzed for SCC by flow cytometry using the Bentley BactoCount instrument [13]. Milk samples were subjected to high-pressure wet mineralization involving microwave-assisted digestion (Mars Xpress 5, Candela, USA), with the use of a mixture of 6 mL of 65% Suprapur nitric acid (Merck, Germany) and 1 mL of 30% Suprapur hydrochloric acid (Merck, Germany), in accordance with the relevant standards. Each sample was analyzed in duplicate. Every mineralization procedure involved 2 blank samples and 2 samples of certified reference material (BCR-063R). The content of elements (K, Na, Ca, Mg, Zn) in the mineralized samples was determined in an atomic absorption spectrometer with flame atomization (SpectrAA240 FS, Candela, USA) [14; 15]. Mineralized milk samples were assayed for the content of Zn, Ca and Mg by atomic absorption spectrometry (AAS) with the use of hollow-cathode lamps (Varian), and for the content of K and Na by atomic emission spectroscopy (AES) with the use of the relevant standards (Sigma-Aldrich, USA).  
The results were processed statistically using Statistica 13.3 software. Milk samples collected at two-week intervals were averaged and pooled into composite monthly samples. The effects of the month of lactation and udder health on daily milk production and the content of K, Ca, Na, Mg and Zn in milk were determined by the least squares method, using the following formula:  
\[Y_{ijk}=\mu+A_{i}+B_{j}+(AB)_{ij}+e_{ij}\]  
where: \(Y_{ijk}\)--value of the analyzed parameter, \(\mu\)--population mean, \(A_{i}\)--effect of the month of lactation (1-5), \(B_{j}\)--effect of udder health (1-4), \((AB)_{ij}\)--month of lactation x udder health interaction, \(e_{ij}\)--random error.  
The significance of differences between means was determined by a Tukey's range test at \(p<0.05\) and \(p<0.01\). Since the empirical distribution of SCC was not normal, the data were log-transformed(the natural logarithm was applied). The Pearson correlation coefficient between the natural logarithm of SCC (In\({}_{\rm{scc}}\)) and the mineral content of milk was calculated.