<p>Feed efficiency is a critical economic trait that influences the productivity, profitability, and sustainability of the livestock industry. The gut microbiota plays a significant role in enhancing intestinal health through various mechanisms, including morphology development, immune responses, dietary nutrient digestion and absorption, and host energy metabolism. These processes ultimately promote animal body weight gain and feed efficiency. Over the past few decades, increasing evidence has underscored the importance of gut microorganisms and their metabolites in animal feed efficiency. However, the mechanisms underlying microbial contribution to this trait remain poorly understood, thereby hindering the development of microbial strategies to enhance animal production efficiency. In this review, we focus on the current research findings related to feed efficiency-associated microbiota in the domestic animals that are most commonly used for human food production. We also discuss the potential molecular mechanisms through which the gut microbiome and postbiotics contribute to feed efficiency, aiming to provide novel insights into future research directions on animal gut microbiome and the development of feasible microbial products to improve feed efficiency in the livestock industry.</p>