PL
W wysoko wydajnej populacji krów rasy czarno-białej przeprowadzono badania składu mleka (tłuszcz i białko). Współczynnik odziedziczalności całożyciowej zawartości tłuszczu wyniósł 0,39, a białka 0,33. U co trzeciej krowy (31,3%) stwierdzono ponad 1% różnicę w zawartości tłuszczu do białka. Odsetek takich zwierząt malał wraz ze wzrostem wydajności mlecznej. Z przeprowadzonych badań wynika konieczność uwzględniania, w programach doskonalenia bydła w typie mlecznym, kwestii składu mleka, a szczególnie udziału w nim białka.
EN
Data of lifetime performance of 1633 cows of Black-White breed, kept in years 1980-1995 in outstanding in dairy performance herd in south-western part of Poland were processed. Cows’ population was divided into groups to make the analysis of eventual changes in milk composition, due to upgrading with HF cattle genes, possible. There were 4 groups: I - pure Black-White cows and with 0.25 share of HF genes (n = 289), II — F₁ cows of B-W x HF (n = 478), III - cows with 0.51 to 0.874 share of HF genes (n = 569), and IV - cows with more than 0.874 share of HF blood (n = 297). Statistical model was used where effect of sire was random and effects of cow‘s genotype group, year of the commencement of dairy performance, reason of culling and regression on age at 1-st calving were fixed. The following values of heritability estimates h² were obtained: milk production from 0.19 to 0.36, lifetime milk fat content = 0.39, lifetime milk protein content = 0.33 and length of performance = 0.28. It was found that every 3-rd cow (31,3%) was characterised with the difference between milk fat and protein contents greater than 1%. Performed analysis of milk composition due to level of milk production and genotype showed that the lowest fat content was characteristic for the highest milk yielding cows, regardless of genotype. Similar relations, but lower in magnitude, were found for milk protein content. It seems urgently needed nowadays to incorporate, with the right accent, milk composition and especially protein content traits to the breeding programs dealing with improvement of dairy type cattle in Poland.