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Dietary fiber is an important component of the raw materials used in the production of feeds for the monogastric market. It is primarily found in by-products, grains, and cereals that are carbohydrate sources in the feed. Some of these carbohydrates are not digested by the digestive enzymes of the small intestine and remain available for bacterial fermentation throughout the intestine, particularly in the large intestine.

As a significant agent whose role is not yet fully understood by the scientific community, and is often overlooked by nutritionists, recent research has explored its function and importance in relation to nutritional digestibility and gut health concerning the microbiota. This research ranges from understanding non-starch polysaccharides (NSPs) that make up different portions of ingredients to addressing the quantitative requirements of various fiber fractions to meet diverse needs.

Polysaccharides in Plant Cell Walls and Their Impact on Metabolism

The polysaccharides that make up plant cell walls vary widely in their chemical composition, intermolecular associations, and chain lengths, leading to differing effects on metabolism and microbiota composition (McRorie et al., 2017; Molist et al., 2014). Due to this heterogeneity, dietary fiber can be classified based on various physicochemical properties, such as water solubility, viscosity, gel formation, water-binding capacity, and fermentability (Blackwood et al., 2000).

Before delving into the research the scientific community has conducted on this fascinating fiber dynamics, it is essential to understand the quantification of raw materials. The most accurate estimation method currently available is the analysis of total dietary fiber, which is the sum of non-starch polysaccharides and lignin. However, obtaining individual monomers through enzymatic and chemical hydrolysis, followed by quantification using gas or liquid chromatography, is time-consuming and labor-intensive. Consequently, transitioning from the traditional concepts of crude fiber (CF) or neutral detergent fiber (NDF)—two widely used methods for quantifying different fiber portions in feed formulations—to the new concepts regarding NSPs is also a costly and lengthy process. Moreover, the roles played by fibers at the metabolic level, within intestinal cells, and in interactions with the microbiota have yet to be fully understood and unraveled.

Despite the diversity of quantification methods leading to results that are difficult to compare in the literature, various aspects at different levels have been investigated regarding the impact of fiber on the nutrition and gut health of monogastrics. According to Spiller (2011), soluble fibers have a high degree of hydration, capable of forming gels and viscous solutions, and they ferment more rapidly compared to insoluble fiber. Kim et al. (2012) and McRorie (2015) added that an increase in the viscosity of the digesta prolongs retention time in the gastrointestinal tract, delaying the interactions between digestive enzymes and nutrients. This slows the breakdown of complex nutrients and the absorption of glucose and other nutrients in the intestinal microvilli (reducing digestibility), which can increase the incidence of diarrhea due to bacterial dysbiosis.

However, some portions of soluble NSPs that do not alter or increase the viscosity of the digesta can be utilized by bacteria in the large intestine, contributing to the production of short-chain fatty acids (SCFAs). When absorbed, these SCFAs provide energy to the animals, creating a cascading effect that reduces the inclusion of net energy in the diet and decreases the production of branched-chain fatty acids, which are indicators of protein fermentation (Kim et al., 2012). For example, in sows, the inclusion of fiber in the diet provides approximately 30% of the net energy needed for maintenance (Serena et al., 2009).

Furthermore, these SCFAs, particularly butyrate and propionate, regulate the production of secretory IgA in the lamina propria and IgG in systemic tissues, stimulating the strengthening of the mucosal barrier as well as the systemic immunity of monogastric animals (Kim et al., 2018).

Insoluble NSPs (cellulose, lignin, and some hemicelluloses), when present in large quantities, are associated with an increased passage rate of digesta through the gastrointestinal tract (GIT). This is due to their ability to retain water molecules, which softens the fecal matter and increases its volume, facilitating intestinal transit and reducing transit time (Spiller, 2001). However, this can also lead to reduced nutritional digestibility and increased endogenous amino acid loss. Conversely, when included in small amounts (2-4%), the reduction in prolonged digesta retention in the GIT decreases the risk of excessive bacterial growth in the small intestine while stimulating feed intake in animals, as the digesta passage rate increases, thus improving performance (Molist et al., 2010).

More specifically, other research has shown that dietary fiber plays a crucial role in the productive and reproductive performance (such as farrowing) of breeding sows. The intense genetic selection for increased prolificacy has resulted in longer farrowing durations, which in turn negatively affects the productive and reproductive parameters of the sow (Björkman et al., 2018) and impacts the vitality, survival, and performance of piglets (Langendijk; Plush, 2019). Thus, nutrition and management during the peripartum period are critical factors related to disturbances in parturition, where the inclusion of fiber is fundamental for systemic health and balance.

In summary, Fischer (2003) concluded that an animal’s response to different types and amounts of dietary fiber is variable and depends on its physiological status, microbial community, environmental conditions, and health status. Similarly, changes in the microbiota of a herd due to environmental stress or an outbreak of clinical or subclinical disease will alter the animal’s response to the various NSP fractions in the diet.

Also, read “Control of Broiler Intestinal Health for Sustainable Production” and check out our Linkedin for updates.