In vitro evaluation of macroalgae as unconventional ingredients in ruminant animal feeds

Abstract

Macroalgae may comprise an alternative feed resource to ruminant animals contributing to a more sustainable livestock production. A wide range of effects on the ruminal fermentation parameters have been reported in short-term in vitro studies, but longer term fermentations are scarce and their effects on the rumen function remain largely unknown. Hypothesizing that ruminal fermentation might be differently affected by the extent of the in vitro fermentations, the present study investigated the effects of Ulva rigida, Gracilaria vermiculophylla, and Saccharina latissima inclusion on gas and methane production, on fermentation parameters, digestibility, and bacterial fatty acids in a RUSITEC system, after a potential adaptation of the rumen microbes to the experimental treatments. Green (U. rigida), red (G. vermiculophylla) or brown (S. latissima) macroalgae produced in an integrated multitrophic aquaculture system were included at 25% (dry matter basis) in a single total mixed ration (TMR) diet and incubated in a RUSITEC system along with a control (100% TMR) over an experimental period of 8 days, following an adaptation period of 7 days. Macroalgae inclusion did not affect gas and methane production. Volatile fatty acids production was not affected by macroalgae but its profile was; the proportion of acetic acid increased and that of propionic acid and butyric acid decreased. Compared to control, macroalgae inclusion only reduced the fermentation efficiency by 1%. The inclusion of macroalgae increased the dry matter and organic matter digestibility, decreased the crude protein digestibility, and did not affect the neutral detergent fiber digestibility. The odd- and branched-fatty acids profile of the bacteria associated to the solid or the liquid fractions was not affected by macroalgae inclusion. Overall, the absence of effects on rumen fermentation suggest U. rigida, G. vermiculophylla, and S. latissima to be suitable alternative feed ingredients to be used in ruminant nutrition up to 25% inclusion.