Nutritional value of microalgae for ruminants and implications from microalgae production.

Abstract Microalgae are a diverse group of microorganisms that are an interesting alternative feed resource for ruminant production. Microalgae species with high protein concentration and adequate amino acid (AA) composition can be used to substitute conventional protein feeds, whereas species with high carbohydrate or lipid concentration can be used to supply energy. Microalgal polyunsaturated acids and short-chain fatty acids have potential to improve the nutritive value of ruminant milk and meat for human consumption and mitigate enteric methane emissions. Microalgae composition is very plastid in comparison to conventional ruminant feeds and it can be influenced relatively easily by environmental conditions, such as nutrient supply. Microalgae also contain many compounds, especially carbohydrates and cell coverings, which are not usually found in ruminant feeds. Standard feed evaluation methods involving the use of crucibles or nylon bags (detergent fibre method, in vitro digestibility and in vivo rumen incubation) suit poorly to the analysis of microalgae with microscopic particle size. This paper attempts to give a general overview of the nutritive value (protein, lipids and carbohydrates) of microalgae for ruminant feeding applications and the possibilities to tailor microalgae composition for a certain ruminant feeding objectives. In addition, the key knowledge gaps related to the nutritive value of microalgae for ruminant nutrition are identified.