Journal of Animal and Feed Sciences, 26, 2017, 359–364 https://doi.org/10.22358/jafs/81275/2017 The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, Jabłonna SHORT COMMUNICATION Effect of freshwater microalgae Nannochloropsis limnetica on the rumen fermentation in vitro D.A. Marrez 1,6 , A. Cieślak 2,6 , R. Gawad 3 , H.M. Ebeid 3 , M. Chrenková 4 , M. Gao 2 , Y.R. Yanza 2 , M. El-Sherbiny 3 and M. Szumacher-Strabel 2,5 1 National Research Centre, Food Toxins and Contaminants Department, Cairo, Egypt 2 Poznań University of Life Sciences, Department of Animal Nutrition and Feed Management, Wołyńska 33, 60-637 Poznań, Poland 3 National Research Centre, Department of Dairy Sciences, 33 Bohouth St., Dokki, 12622 Giza, Egypt 4 National Agricultural and Food Centre, Hlohovecká 2, 95141, Nitra-Lužianky, Slovakia KEY WORDS: microalgae, rumen, in vitro, fermentation, fatty acids Introduction Algae have been found to be a valuable feed source for poultry, fsh and pigs (Kotrbáček et al., 2015). However, there is no comprehensive research on the use of algae in ruminant nutrition and their effect on rumen functions (da Silva et al., 2016). There is also lack of research on specifc freshwater microalgae Nannochloropsis limnetica as potential feed additive, especially for ruminants. The main advantage of the microalgae, compared to common algae is the ability to produce highly valuable mol- ecules such as n-3 fatty acids (FA), especially doco- sahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) (Spolaore et al., 2006). The FA composition of the freshwater microalgae species N. limnetica is similar to that of marine species, however, the to- tal amount of FA is higher than in marine species (Krienitz et al., 2000). In the study of Costa et al. (2016) whole or post-lipid extraction microalgae were used as a potential crude protein supplement for cattle. ABSTRACT. It was hypothesised that Nannochloropsis limnetica due to the specifc chemical composition and fatty acids profle, may positively affect ru- men fermentation. To confrm this hypothesis the batch culture experiment was conducted to evaluate N. limnetica supplemented at 0, 2, 4 and 6% of the substrate dry matter (DM) on both fermentation and fatty acid propor- tion in the ruminal culture. It was found that microalgae N. limnetica contain (g · kg −1 DM): crude protein 238, Ca 48.7, Na 31.8 and unsaturated fatty acids (51.7 g · 100 g −1 fatty acids). Moreover, leucine and lysine were the most abun- dant essential amino acids in the analysed microalgae. The total bacteria count was negatively affected if N. limnetica algae were supplemented at more than 4%. So, the research hypothesis that microalgae N. limnetica may affect rumen fermentation was confrmed, mainly by increasing propionic acid concentra- tion without changes in the total volatile fatty acids concentration. However, a high dose (6%) decreased rumen bacteria count. Further research under commercial farm conditions should be conducted to confrm the usefulness of freshwater microalgae N. limnetica as a feed additive for ruminants. Received: 24 July 2017 Revised: 5 December 2017 Accepted: 16 December 2017 5 Corresponding author: e-mail: mstrabel@up.poznan.pl 6 Equal contribution