The aim of this study was to determine the genetic effect of cow breed on the yield and quality of cow's milk. On the selected dairy farm, cows of two different breeds Montbeliarde and Polish Holstein-Friesian between 45th -100 th days of lactation, were managed under the same environmental conditions. Milk samples were collected twice (in May and June 2008) from 97 (n = 51 and 46 for Montbeliarde and Polish Holstein-Friesian, respectively) cows. Montbeliarde cow's milk was characterized by significantly lower milk yield and somatic cell count. Higher level of C18: 2 cis-9 trans-11 and almost 2-fold C20:5 n-3 (P ≤ 0.01) was also recorded. However, Polish Holstein-Friesian cow's milk had a better composition of protein fraction (higher concentration of lactoferrin, α-lactoalbumin and β-lactoglobulin) and higher concentrations of vitamins D and E. Moreover, milk of Polish Holstein-Friesian breed was characterized by more favorable fat fraction with significantly lower concentrations of saturated fatty acids (C14:0, C18:0) as well as lower atherogenic and thrombogenic indexes and higher concentration of C18:2 trans-10 cis-12, C20:3 n-6 and C 22:6 n-3. This study was the first one comparing biological quality of Polish Holstein-Friesian and Montbeliarde milk under the same environmental conditions in Polish production systems. Cattle, somatic cell count, fatty acid, whey proteins, vitamins soluble in fat

Linseed variety significantly influenced the lipid fraction level and the basic chemical composition of cow's milk. Linseed variety should therefore be taken into consideration in subsequent experiments in addition to the quantity and physical form of linseed. The results showed that the use of a diet supplemented with linseed, especially the Szafir variety, was effective in reducing saturation, atherogenic and thrombogenic indices, yielding benefits for consumers by improving the nutritional quality of cow's milk.

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Modification of the diet of cows with fish oil and linseed significantly influenced antioxidant properties of their milk; however, the response of multiparous and primaparous cows was noticeably different to the supplement introduced.