Variability of in vitro ruminal fermentation and nutritional value of cell-disrupted and nondisrupted microalgae for ruminants

Abstract

The objective of this study was to investigate ruminal fermentation and the nutritional value of different microalgae products (MAP) for ruminants, including inter- and intra-genera variability. Furthermore, the effect of mechanical cell disruption was also evaluated. Cell-disrupted and nondisrupted MAP of four genera were investigated using the Hohenheim Gas Test. The investigations included characterization of gas production (GP), production of volatile fatty acids (VFA) and methane, organic matter digestibility, and energetic value as well as utilizable crude protein at the duodenum and ruminally undegradable crude protein (RUP). Furthermore, a three-step enzymatic in vitro system was used to estimate intestinal digestibility of RUP (IDP). Ruminal fermentation was low for all investigated microalgae genera, as indicated by overall low GP, low production of VFA, and low ruminal protein degradation. Nevertheless, all microalgae genera were characterized by high RUP concentrations (236–407 g/kg dry matter; passage rate = 8% hr −1 ), indicating that microalgae might be a promising protein source for high-performing ruminants. Low IDP (26%–49% of RUP) considerably contradicted this potential. Mechanical cell disruption in general enhanced the extent of ruminal fermentation of MAP but, as RUP was decreased and IDP was hardly affected, mechanical cell disruption appears not to be necessary when microalgae are intended for application as a protein source for ruminants. Because of the high variability in the characteristics of the nutritional value, general means are inappropriate to characterize the nutritional value of MAP. In conclusion, suitability of microalgae as a protein source for ruminants might be limited because of low IDP, although further studies are necessary to prove these findings in vivo.