Use of microalgae in ruminant nutrition and implications on milk quality - A review

Microalgae are photoautotroph unicellular or multicellular microorganisms which are smaller than 400 μm and can be used as an animal feed source. Ruminants seem to be promising targets of this new feedstuff, as they can also use non-protein nitrogens present in algae and digest the cell walls of algal organisms. Despite the potential for use of microalgae in ruminant feeding, to our knowledge the applications are still limited and there are no reviews in the literature on the effects of microalgae on milk yield and quality. This paper reviews the studies on the use of microalgae for dairy ruminant feeding in order to provide complete information on the state of the art, limitations, and their potential use. The major effects of microalgae on milk production are the changes in the milk fatty acid profile, especially related to the long chain fatty acids and the omega 3 series, in particular DHA and EPA which are beneficial for human health. These results are interesting as to date attempts to increase the omega 3 content in milk by feeding have led to limited results, since PUFA biohydrogenation in the rumen is massive. However, excessive algal supplementation might negatively impacts on palatability, feed intake, the ruminal metabolism and may have negative effecs on milk production and fat. In conclusion, careful attention should be paied in terms of the amount of algae supplemented and ruminoprotected forms should be considered in order to prevent reductions in the feed intake, and a deterioration in milk yield and quality. Further reseach is needed to identify the more appropriate species/feed and the effects of a prolonged supplementation.