Bioconversion of green algae Ulva lactuca biomass with Saccharomyces cerevisiae yeast and exogenous fibrolytic enzymes into suitable ruminant feed

Ulva lactuca algae is a fast-growing aquatic biomass that poses a serious problem to marine ecosystem and ecology. It is characterized by a high content of protein, fiber, and important antioxidant activity. However, its low fiber digestibility (22%) and net energy available for lactation (2.2 MJ/kg dry matter) are the main obstacle for large-scale integration in ruminant diets. Therefore, this research was conducted to improve their nutritional value by pretreated them for 24 h with exogenous fibrolytic enzymes (EFE) and Saccharomyces cerevisiae yeast (SCY) at two doses (0 and 4 mg/g dry matter) in a 2 × 2 factorial arrangement. Pretreatment with EFE bioconverted some fiber to simple sugars and enhanced rumen microbiota, resulting in increase in ruminal fermentation, fiber digestibility by 11%, and net energy available for lactation by 17%, and depress ruminal pH. Pretreatment with SCY lowers its polyphenol and improves rumen bacteria, resulting in increase in rumen fermentation, fiber digestibility by 6%, and net energy available for lactation by 12% without altering rumen pH. A synergistic interaction between EFE and SCY was observed, resulting in increase in fiber digestibility by 16%, net energy available for lactation by 32%, and conversion of ammonia–nitrogen to microbial crude protein without altering rumen pH. Ultimately, pretreatment of Ulva lactuca with EFE + SCY is an eco-friendly strategy to convert this abundant biomass into a cost-effective and suitable ruminant feed that does not compete with human demand for fertile farmland and freshwater resources. This strategy can be explored on a large-scale in future to evaluate its impact on ruminant performance and product quality. Graphical abstract: [Figure not available: see fulltext.].