The aim of this study was to analyse the effect of supplementary feeding of DHA (Docosahexaenoic Acid) rich algae product (Algae STM Alltech Inc.) on production of milk, fat and protein as well as on reproduction of high yielding Holstein dairy herd. Field trial was set up on Top 10 dairy farm in western part of Slovakia, under commercial conditions. The data of high yielding dairy cows, separated in two groups of 30 (control) and 29 (trial) animals, were recorded for period of 3 subsequent months from October to December 2015. Animals were fed once a day Total Mixed Ration based diet with different feed mixture composition in trial group (+100 g Algae STM Alltech Inc. per cow and day). Performance data were collected in accordance with official milk recording system of Breeding Services of Slovak Republic s. e. and milk samples were collected once per month according to the A4 standard methodology. The control group showed higher level of milk production compared to trial. Our study indicated that the feeding of algae caused milk fat depression and generally lower protein content in milk. Significant impact of algae feeding was found also for the level of urea in milk. In addition, the supplementary feeding of DHA may represent effective strategy to increase the percentage of pregnancies per inseminations in lactating dairy cows.