AbstractDefining and quantifying amino acid requirements will become an important consideration in the next generation of feeding schemes for dairy cattle beyond the current emphasis on identification of limiting amino acids. In this context different amino acid profiles of untreated, urea treated, fungal treated, and urea plus fungal treated lignocellulosic feed by both P. ostreatus wild and its two cellulase-minus/ less lignolytic mutants were analyzed. Cellulase-free mutant strains were obtained after 20 minutes of exposure to UV light and 0.4 seconds to X-rays. A UV mutant of P. ostreatus (POM1) exhibited better performance than the X-ray mutant (POM2) in terms of production of less cellulolytic and more lignolytic enzymes. Urea treatment of straw enhanced the total amino acid content by less than a factor of two, while the fungal treatment improved it by 13-14 times. Fungal treatment of urea-treated straw improved the total amino acid content by a factor of 15, indicating the importance of urea in the straw. Further, the fungal treatment of urea-treated straw enhanced the quantity of amino acids such as glutamine, glycine, aspergine, etc. by 15-20 times. The quantity of limiting amino acids such as methionine, lysine, and histidine was also enhanced by 8 to 10 times through the fungal treatment. Maximum amounts of all the amino acids were found in urea plus fungal (POM1) treated paddy straw than in only fungal treated and only urea treated paddy straws.