Sequential fermentation of wheat straw and fruit-vegetable discards to produce circular feed in support of sustainable dairy production

Developing novel circular feed from plant-based biomass unfit for direct human consumption is imperative to mitigate environmental degradation. In this study, we tested a sequential fermentation strategy to treat wheat straw (WS) and preserve fresh fruit and vegetable (FFV) discards in making circular feed for ruminants. First, ground wheat straw (particle size <20 mm) moisturized (moisture content 70–80 % by weight) by pure water and by FFV were treated with feed grade fungal strains Tramates versicolor (TV) and Pleurotus ostreatus (PO) at 28 °C for six weeks. Fungal treated mixture resulted in reduced lignin content by 35–55 % and decreased lignin-to-cellulose ratio. Each fungal treated biomass was then mixed with additional FFV and anaerobically fermented at 28 °C for 16 days. Organic acids (over 80 % was lactic acid) accounted for 9–10 % dry matter of the substrates and lowered pH from 5 to about 3.5, which is adequate for preservation of the fermented feed. In vitro dry matter digestibility was not different between the standard diet and sustainability-plus diets that contained 10 % or 25 % of the double-fermented circular feed materials. Fungal fermentation coupled with bacteria-based ensiling of under-valued or wasted biomass can produce novel feeds to support sustainable dairy farming.