146 Rethinking fiber in nursery pig nutrition - balancing benefits and challenges.

Abstract Dietary fiber comprises a diverse group of cell wall polysaccharides, along with lignin, that resist digestion by endogenous enzymes in non-ruminants. Despite extensive research efforts over the past several decades, fiber remains one of the most challenging nutritional components to define, analyze, and apply effectively in nursery pig diets. Recently, fiber has gained attention as a functional ingredient in nursery pig diets, with its benefits closely linked to physicochemical characteristics such as fermentability, viscosity, and hydration capacities. While analytical advances have improved our chemical understanding of dietary fiber sources, translating these insights into clear beneficial outcomes and practical nutritional recommendations remains complex. Further complicating matters, nursery pigs face unique digestive and immunological challenges, particularly during the critical early post-weaning period. Enteric pathogens pose substantial risks to weaned pig health, leading to compromised growth performance and increased incidences of scouring. Moreover, post-weaning feed intake is low and variable, making dietary fiber inclusion potentially counterproductive by diluting nutrient density. Even with these limitations, there is a body of evidence suggesting dietary fiber can reduce pathogen burden, improve intestinal health and fecal consistency, and enhance pathogen-binding capacity. Additionally, certain fiber sources beneficially modulate gut microbial populations, potentially promoting overall gastrointestinal resilience. However, the effectiveness of dietary fiber varies considerably based on fiber type. Soluble fibers may enhance hindgut fermentation and short-chain fatty acid production but can ferment too rapidly for nursery pigs with limited digestive maturity. Conversely, insoluble fibers may contribute by reducing harmful hindgut protein fermentation, binding pathogenic bacteria, and even preventing their colonization. However, such positive responses in both fiber types have typically been observed in older weaned pigs, healthier herds, or in diets containing small grains and higher baseline fiber levels than those commonly utilized in US nursery pig diets. Recent US studies have indicated that inclusion of fiber-rich ingredients such as oat groats, wheat middlings, soy hulls, sugar beet pulp, wheat bran, among others, in nursery pig diets experiencing enteric health challenges do not yield tangible improvements in nursery pig performance, fecal scores, or gut health. Collectively, these findings highlight the necessity of carefully considering production systems, health status, fiber type, source, and context for practical application in nursery diets. This presentation will focus on navigating the complexities associated with dietary fiber use in nursery pig nutrition, emphasizing the integration of analytical, chemical, and physiological insights, while also considering the situational dependencies inherent to production systems and outlining future research directions for practical and effective fiber use.