Sustainability of feeding plant by-products: A review of the implications for ruminant meat production

Ruminant meat production is associated with a large environmental cost compared to other livestock products. Feed production, transport, and utilisation play a major role in global food security and greenhouse gas emissions from livestock production. Replacement of edible feed crops with human-inedible biomass in animal diets is a potential strategy that could reduce food-feed competition and mitigate the environmental impacts of livestock. Globally, plant by-products (PBP) represent an important human-inedible feed resource for livestock production. These waste streams can be obtained from agro-industrial processes such as distillery and biofuel production, oilseed processing, fruit and vegetable processing, sugar production, root and tuber processing, and herb, spice and tree processing. The microbial population in the forestomach (rumen) of ruminants allow PBP to be used effectively compared to monogastric livestock. Assessing and improving the utilisation of PBP may enhance the environmental sustainability of ruminant meat production without compromising the quality attributes and consumer acceptability of meat. Some PBP contain a considerable amount of residual bioactive compounds such as vitamins, unsaturated fatty acids, and phytochemicals. Feeding innovations based on the utilisation of bioactive-rich PBP may reduce enteric methane and nitrogen emissions in ruminants while improving the nutritional composition and shelf-life quality of meat and meat products. This review examines the dual-impact of dietary PBP on environmental sustainability and meat quality attributes in ruminant production. In addition, the paper highlights the implications of this alternative feeding strategy on meat safety and the strategic interventions pertinent to its practical application for ruminant meat production.