Although common coproducts such as dried distillers grain with solubles (DDGS), wheat middlings, sugar beet pulp and soybean hulls are economically priced, the concentration of dietary fiber (DF) in these coproducts limits the ability of pigs to use energy and nutrients, thereby reducing caloric efficiency.
More recently, and because of this functional characteristic, feeding high-fiber diets has been used as a strategy to slow the growth of pigs to avoid oversupplying U.S. pork processing plants due to the COVID-19 pandemic.
As a result of the many diverse properties of DF, it has become a popular topic among scientists, nutritionists and pork producers.
Because our current knowledge on fiber classification, functionalities and sources is limited, our ability to predict the impacts of feeding fibrous coproducts on growth, physiological responses and intestinal function of pigs is still in its infancy.
Because chemical structures and functions of fibers are not identical, the term DF is used to describe the total content of carbohydrates in a feed ingredient that is indigestible in the small intestine. Based on the chemical structure of plant carbohydrates, DF is the sum of nonstarch polysaccharides plus lignin (Choct, 2015).
Therefore, total dietary fiber, which is the sum of soluble and insoluble fiber, is the most suitable analytical assay that fits the functional definition compared with other common measurements such as crude fiber and neutral detergent fiber.
Traditionally, the fiber concentration obtained from chemical analysis has been monitored when formulating swine diets because of the inverse relationship between fiber content and nutrient digestibility in pigs (Moeser and Van Kempen, 2002).
However, these fiber measurements do not provide sufficient information on physiological effects of DF that may be used to improve the accuracy of estimating effects of fiber intake on energy digestibility, satiety and intestinal function and health status.
Saqui-Salces et al. (2017) and Vila et al. (2018) reported that pigs fed similar amounts of DF from different fiber sources exhibited different physiological responses, such as changes in intestinal nutrient sensors and transporters, mucin expression and immune responses.
These results suggest that determining the chemical composition of DF is insufficient for understanding its effects on physiological responses.
Indeed, fiber structure and physical-chemical properties impact physiological responses and nutrient metabolism that play a significant role in production performance (Guillon and Champ, 2000).
Among physical-chemical properties of DF, viscosity has a strong effect on digestive physiology.
Effects include but are not limited to the flow behavior of digesta (e.g., mean retention time; Schop et al., 2020); influence of digestibility…