Impact of Dietary β-Mannans on the Intestinal-Nutritional Interface and Growth Performance of Chickens and Pigs: Challenges and Strategies via Exogenous β-Mannanase Based on Meta-Analysis.

The objectives of this review were to elucidate the physiological challenges induced by dietary β-mannans and to review the underlying modes of action of exogenous β-mannanase on the intestinal microbiota, intestinal health, nutrient utilization, and growth performance of chickens and pigs. The highly branched structure of β-mannans, particularly those with a high proportion of soluble β-mannans, can increase digesta viscosity and negatively modulate intestinal health by increasing the abundance of opportunistic pathogenic microbiota and reducing the abundance of bacteria associated with favorable metabolic outputs, such as short-chain fatty acids, in the small intestine. Furthermore, intact β-mannans are recognized by the intestinal immune system due to structural similarity to pathogen-associated molecular patterns in the small intestine, triggering unnecessary inflammatory responses. These combined factors damage intestinal structure and tight junction proteins and reduce nutrient utilization and growth performance in monogastric animals. Dietary β-mannanase supplementation can mitigate these challenges by breaking down the β-mannan structure. This enzymatic action reduces digesta viscosity and increases prebiotic manno-oligosaccharides in the small intestine, which positively modulates the diversity and abundance of intestinal microbiota, reduces immune responses, enhances intestinal barrier function and structure, and increases nutrient utilization. These gastrointestinal improvements enhance growth performance. Meta-analysis using a log response ratio scale (lnRR) showed that as dietary β-mannans increased, the mitigating effects of β-mannanase on intestinal health and growth performance of chickens became pronounced. When back-transformed to the percentage scale [(e