The Diamond V XPO preparation is obtained in fermentation process of corn grains with use of Saccharomyces cerevisiae yeast. The experimental material constituted 60 dairy cows of Black-and-White breed upgraded with 70-90% of HF. The animals were kept on straw in the stanchion barn. The cows were by analogue method divided into two experimental groups, and feed during whole year with the same diets. Cows from experimental group additionally received Diamond V XP preparation, given individually to the animal at dose 60 gּdayּhead^-1 in dry period and 100 gּdayּhead^-1 during lactation. Once per month during 305 days of lactation milk yield and composition were controlled. For cows received in daily ration addition Diamond V XP daily milk yield during 3 month of lactation were by 3.7 kg higher. The milk yield for 305 days of lactation was 9976 kg and was by 686 kg higher than in control group. There was no influence of Diamond application on milk composition. During 2 months of lactation the level of minerals in milk and blood serum were higher.

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