Biological treatment of crop residues for ruminant feeding: A review

Crop residues are often referred to as ‘lignocellulosics’ as they are rich in cellulose which is bound with a biopolymer lignin. Rumen microbiota (bacteria, protozoa and fungi), even with their hydrolytic enzymes, are not very competent enough to break these bonds efficiently. Biological treatment of such crop residues using white rot fungi (WRF) can break the ligno-cellulose complexes, liberating free cellulose and thus enhancing their feeding value for ruminants. Biologically treated roughages have higher digestibility for most of the nutrients (both cell walls and cell solubles) with an increase in crude protein content as compared to untreated material, besides ensuring more fermentable substrates in the rumen. Further, recent studies have indicated low methane emission from feedstuffs subjected to solid state fermentation (SSF) with ligninolytic fungi as a result of their improved digestion and nutrient assimilation. This review primarily deals with the nature and composition of crop residues, their inherent nutritive constraints as ruminant feed and to overcome the same by means of biological treatments. The progresses to date in in vitro and in vivostudies on biologically treated lignocellulosics have also been reviewed. Key words: Crop residues, ligninolytic fungi, ruminant, digestibility, methane.