Genetic engineering approaches to address lignin-related challenges in ruminants feeding: Implications for environmental and animal health

Lignocellulosic straw from cereal crops such as wheat, rice, maize, and barley constitute one of the most abundant yet underutilized agricultural residues globally, offering a renewable, low-cost feedstock for ruminants nutrition. However, its high lignin content limits microbial access to cellulose and hemicellulose, while the limited capacity of the rumen microbiome to degrade lignin contributes to poor feed efficiency, reduced animal productivity, methane emissions, and crop-residue burning. This review explores the potential of genetic engineering to develop genetically modified ruminants capable of producing synthetic lignin-degrading enzymes in saliva, thereby facilitating lignin breakdown in the oral cavity and enhancing straw utilization. The biochemical challenges to lignocellulose degradation, existing lignin-degradation mechanisms in ruminants, and proof-of-concept evidence from transgenic models are examined, with emphasis on their implications for feed efficiency, livestock productivity, and environmental sustainability. The available evidence indicates that expressing lignin-degrading enzymes in ruminants could improve the utilization of crop residues by making cellulose and hemicellulose more accessible, thereby reducing feed costs, improving animal productivity and promote environmental sustainability. With proper safety evaluation and suitable feeding and management practices, this approach could offer a promising strategy for better and more sustainable utilization of cereal crop residues in ruminants.