In vitro evaluation of microalgae as a source of polyunsaturated fatty acids for ruminants

Abstract Microalgae may be adequate sources of polyunsaturated fatty acids (PUFA) for ruminants, but information regarding their dry matter (DM) digestibility is still scarce. The in vitro digestibility of various dried PUFA-rich microalgae for ruminants ( Arthrospira platensis , Nannochloropsis gaditana , Scenedesmus almeriensis , Tetraselmis chuii , and Tisochrysis lutea ) was evaluated and the ruminal biohydrogenation of their PUFA assessed. All microalgae had high content of ash (> 78.1 g kg -1 DM), total nitrogen (> 66.3 g kg -1 DM) and ether extract (> 122 g kg -1 DM). The highest levels of α-linolenic acid (C18:3 n -3), eicosapentaenoic acid (C20:5 n -3), and docosahexaenoic acid (C22:6 n -3) were found in S. almeriensis , N. gaditana , and T. lutea , respectively. Most PUFA of microalgae were extensively biohydrogenated by ruminal microorganisms, but biohydrogenation of C20:5 n -3 in N. gaditana and C22:6 n -3 in T. lutea was lower, suggesting that a substantial amount of these PUFA can escape the rumen unaffected. The in vitro total DM digestibility (TDMD) of microalgae was high (from 538 to 970 g kg -1 DM). The proportion of DM digested in the rumen in relation to TDMD ranged from 49.3 to 64.5%, indicating that a considerable DM digestion occurred in the intestine. Therefore, the microalgae N. gaditana and T. lutea are efficient nutritional sources of bypass C20:5 n -3 and C22:6 n -3 fatty acids, respectively, for ruminants.