The experiment was conducted on 26 nursing Kamieniec ewes from a breeding herd. The animals were divided into two equal groups characterized by the same litter type, age and sex of suckling lambs: I – control and II – experimental. Throughout the 70-day lactation period, both groups were fed identical diets comprising haylage of grasses and legumes, meadow hay and CJ concentrate in daily rations of: 2.80 kg haylage of grasses and legumes, 0.6 kg meadow hay and 0.6 kg CJ concentrate per ewe. Group II animals were fed the CJ concentrate with the addition of Inter Yeast S® Saccharomyces cerevisiae dried yeast in the amount of 50 g kg–1 of the concentrate. Milk was sampled during control milking runs on lactation day 28 and 70. The collected samples were analyzed to determine the content of protein, whey protein, casein, αs, β and κ casein fractions. Blood was sampled twice from the jugular vein on lactation day 28 and 70. After separation of serum, the following nutrient concentrations were determined: inorganic phosphorus (Pin), calcium (Ca) and magnesium (Mg). No significant variations were reported in the percentage share of whey proteins in ewe’s milk during the peak and towards the end of lactation. The yeast preparation had no effect on the casein content of milk. Yeast supplementation si gnificantly influenced the proportions of casein fractions on lactation day 70. A significant drop in β-casein levels (by 2.32%) with a simultaneous increase in κ-casein concentrations (by 1.86%) were noted in the milk of group II animals. Similar calcium, phosphorus and magnesium concentrations were determined in the blood serum of both animal groups throughout the experiment (on lactation day 28 and 70) and these results were within the reference values. The results of this study indicate that the inclusion of Saccharomyces cerevisiae brewer’s yeast into the diet of lactating ewes could enhance the quality of milk proteins.

   17.1.2012