## 2 Materials and Methods  
The study material was the milk of 30 cows of two breeds, Montbeliarde (mb; \(n\) = 15) and black-and-white Polish Holstein-Friesian (phf; \(n\) = 15), kept at the same farm. The phf cows were matched with the mb cows by analogs considering the stage and number of successive lactations. The mean number of lactations of all cows reached 2.3 \(\pm\) 0.65. All cows calved in the spring-summer season. The animals were housed in a stanchion barn with feeding alleys alongside the lateral walls of the building. They were fed in a traditional system with feed mixtures prepared at the farm (maize silage and the pre-wilted silage of grasses) and the addition of feed concentrates. In the spring-summer period, the cows grazed on pasture and received maize silage and feed concentrates in the barn. The feed samples were collected, and the chemical composition of the diets fed to the cows was determined by standard methods [13] (Table 1). The ingredients and chemical composition of the diets are given in Table 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Traits**} & \multicolumn{5}{c}{**Feeds**} \\ \cline{2-6}  & **Pasture** & **Haylage** & **Meadow Hay** & **Maize Silage** & **Concentrate** \\ \cline{2-6}  & \multicolumn{5}{c}{**Chemical Composition (\% in Fresh)**} \\ \hline Dry matter (DM) & 22.32 \(\pm\) 2.98 & 48.81 \(\pm\) 0.34 & 72.41 \(\pm\) 0.53 & 33.31 \(\pm\) 0.35 & 88.04 \(\pm\) 0.54 \\ Ash & 1.87 \(\pm\) 0.31 & 3.33 \(\pm\) 0.13 & 5.23 \(\pm\) 0.17 & 1.27 \(\pm\) 0.06 & 5.59 \(\pm\) 0.16 \\ Crude protein & 3.27 \(\pm\) 0.69 & 7.24 \(\pm\) 0.11 & 5.98 \(\pm\) 0.14 & 2.84 \(\pm\) 0.11 & 19.63 \(\pm\) 0.21 \\ in 1000 g of DM & 146.6 \(\pm\) 3.83 & 148.4 \(\pm\) 2.92 & 82.6 \(\pm\) 1.53 & 85.3 \(\pm\) 1.36 & 222.7 \(\pm\) 3.54 \\ Crude fat & 0.19 \(\pm\) 0.04 & 1.01 \(\pm\) 0.06 & 1.22 \(\pm\) 0.04 & 0.97 \(\pm\) 0.08 & 2.81 \(\pm\) 0.08 \\ Crude fiber & 5.58 \(\pm\) 0.67 & 14.24 \(\pm\) 0.15 & 24.53 \(\pm\) 0.31 & 7.36 \(\pm\) 0.21 & 8.68 \(\pm\) 0.13 \\ in 1000 g of DM & 250.2 \(\pm\) 2.58 & 291.1 \(\pm\) 1.93 & 338.3 \(\pm\) 3.83 & 221.1 \(\pm\) 2.67 & 98.6 \(\pm\) 0.95 \\ ADF & 310 \(\pm\) 4.13 & 271 \(\pm\) 2.35 & 324 \(\pm\) 2.87 & 211 \(\pm\) 2.57 & 41 \(\pm\) 0.33 \\ FUL & 0.74 \(\pm\) 0.03 & 0.84 \(\pm\) 0.05 & 0.72 \(\pm\) 0.02 & 0.88 \(\pm\) 0.03 & 1.02 \(\pm\) 0.04 \\ PDIN & 79 \(\pm\) 0.72 & 93 \(\pm\) 0.83 & 66 \(\pm\) 0.68 & 52 \(\pm\) 0.59 & 139 \(\pm\) 0.86 \\ PDIE & 82 \(\pm\) 0.73 & 72 \(\pm\) 0.54 & 78 \(\pm\) 0.62 & 67 \(\pm\) 0.53 & 137 \(\pm\) 0.77 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of feeds used for the dairy herd (mean \(\pm\) standard deviation). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Item** & **Winter Period** & **Summer Period** \\ \hline Pasture & - & 9.6 \\ Maize silage & 5.5 & 3.4 \\ Haylage & 7.5 & - \\ Meadow hay & 3 & 3 \\ Concentrate & 2 & 2 \\ Dry matter (g/kg) & 523.6 \(\pm\) 0.83 & 429.7 \(\pm\) 0.76 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Ingredients (kg DM) and chemical composition of diet (mean \(\pm\) standard deviation). Milk for analysis was collected from each cow six times during lactation on the 1 st, 2 nd, 5 th, 6 th, 9 th and 10 th month of lactation. Milking was performed twice a day using a milking pipeline machine. Representative milk samples were collected during the official test milking. Approximately 50 mL milk samples were collected in glass containers with 1 mL (20% \(w/v\)) of 2-bromo-2-nitropro-pane-1,3-diol (bronopol; VWR International AB, Stockholm, Sweden). The milk samples were transported at a refrigeration temperature to the laboratory. The fresh milk was analyzed for its proximate chemical composition (protein, fat, lactose and dry matter) using the infrared spectrophotometry method with a MilkoSan FT 120 apparatus (FossElectric, Hillered, Denmark), and for the somatic cell count (SCC), the method of flow absorption was employed using a BactoCount apparatus (Bentley, Maroeuil, France).