## 3 Results  
Analysis of the milk samples in terms of performance and proximate composition demonstrates statistically significant differences between breeds (Table 3). The phf cows were characterized by a higher milk yield than the mb cows (23.2 kg vs. 21.7 kg). However, the milk samples from mb cows compared to the milk of phf cows had higher contents of all basic milk constituents. Significant differences were, however, only determined for the contents of lactose (\(p\leq 0.01\)) and fat (\(p\leq 0.05\)). A higher content of potassium was assayed in the milk of phf cows (1623.79 mg/L) compared to mb cows (1564.38 mg/L), but the difference was not confirmed statistically (Table 4). The milk of mb cows was, in turn, characterized by significantly higher contents of sodium, magnesium, calcium and zinc than the milk from phf cows (\(p\leq 0.01\)). The highest content of potassium was noted in milk from the middle stage of lactation of the phf breed (1674.82 mg/L; Table 5), and, together with the content in milk from the late stage of lactation, it was significantly higher than in the early stage (\(p\leq 0.01\)). The highest contents of magnesium and calcium were noted in milk from the early stage of lactation of the phf breed (95.87 mg/L and 870.90 mg/L, respectively). Statistical differences were confirmed between the early and the middle (\(p\leq 0.05\)) and late (\(p\leq 0.01\)) stages of lactation for magnesium and between the early and late (\(p\leq 0.05\)) stages of lactation for calcium. A significantly higher (\(p\leq 0.05\)) content of zinc was noted in milk from the middle stage of lactation (4.59 mg/L) compared to the late stage (3.84 mg/L). \begin{table}
\begin{tabular}{c c c c} \hline
**Specification** & **Average** & **phf** & **mb** \\ \hline
**Number of Samples** & **180** & **90** & **90** \\ \hline K (mg/L) & 1596.40 \(\pm\) 175.05 & 1623.79 \(\pm\) 158.15 & 1564.38 \(\pm\) 189.92 & 0.111 \\ Na (mg/L) & 451.45 \(\pm\) 96.18 & 419.86 \(\pm\) 49.54 & 488.45 \(\pm\) 91.93 & 0.001 \\ Mg (mg/L) & 96.09 \(\pm\) 15.73 & 87.74 \(\pm\) 10.56 & 105.88 \(\pm\) 15.22 & 0.000 \\ Ca (mg/L) & 854.15 \(\pm\) 200.26 & 763.48 \(\pm\) 172.12 & 960.30 \(\pm\) 178.88 & 0.000 \\ Zn (mg/L) & 4.54 \(\pm\) 1.07 & 4.08 \(\pm\) 0.99 & 5.08 \(\pm\) 0.90 & 0.000 \\ \hline \end{tabular}
\end{table} 
Table 4: Mineral composition of milk from different breeds (mean \(\pm\) standard deviation). \begin{table}
\begin{tabular}{c c c c c} \hline
**Specification** & **Average** & **phf** & **mb** & \\ \hline
**Number of Samples** & **180** & **90** & **90** & **\(p\)-Value** \\ \hline Daily yield (kg) & 22.82 \(\pm\) 6.81 & 23.2 \(\pm\) 7.3 & 21.7 \(\pm\) 6.2 & 0.309 \\ SCC/mL & 442.56 \(\pm\) 1112.62 & 383.3 \(\pm\) 7.06 & 496.7 \(\pm\) 1390.3 & 0.636 \\ LnSCC & 5.34 \(\pm\) 0.99 & 5.24 \(\pm\) 1.05 & 5.43 \(\pm\) 0.95 & 0.378 \\ Fat (\%) & 3.63 \(\pm\) 0.91 & 3.44 \(\pm\) 0.85 & 3.81 \(\pm\) 0.94 & 0.041 \\ Protein (\%) & 3.29 \(\pm\) 0.38 & 3.28 \(\pm\) 0.40 & 3.30 \(\pm\) 0.36 & 0.785 \\ Casein (\%) & 2.93 \(\pm\) 0.45 & 2.87 \(\pm\) 0.47 & 2.99 \(\pm\) 0.43 & 0.195 \\ Lactose (\%) & 4.73 \(\pm\) 0.15 & 4.68 \(\pm\) 0.13 & 4.78 \(\pm\) 0.15 & 0.001 \\ Dry matter (\%) & 12.35 \(\pm\) 1.03 & 12.11 \(\pm\) 0.98 & 12.58 \(\pm\) 1.19 & 0.239 \\ Non-fat dry matter (\%) & 8.72 \(\pm\) 0.36 & 8.76 \(\pm\) 0.36 & 8.68 \(\pm\) 0.35 & 0.269 \\ \hline \end{tabular}
\end{table} 
Table 3: Milk yield and proximate chemical composition depending on breed (mean \(\pm\) standard deviation). Similar to the milk of phf cows, in the milk of mb cows, the highest content of potassium was noted in milk from the middle stage of lactation (1655.14 mg/L). However, statistical differences were only confirmed between the middle and late (\(p\leq 0.05\)) stages of lactation (Table 6). The opposite situation was the case regarding the sodium content in the milk of mb cows; the lowest content of this element was recorded in the middle phase of lactation (428.92 mg/L), and it was significantly (\(p\leq 0.05\)) lower than in the early and late stages of lactation.