PSI-18 - Soluble dietary fiber, insoluble dietary fiber, and total dietary fiber in feed ingredients used in swine diets

Abstract: Dietary fiber is defined as the undigestible carbohydrates and lignin fractions of plant-feed ingredients. The most complete and representative analysis of fiber is the total dietary fiber (TDF) analysis, which includes the soluble dietary fiber (SDF) and the insoluble dietary fiber (IDF). There is, however, a lack of data for concentrations of SDF, IDF, and TDF in feed ingredients commonly used in diets for pigs. Therefore, work was conducted to quantify fiber fractions of plant feed ingredients to establish a database for SDF, IDF, and TDF in feed ingredients commonly used in animal nutrition. A total of 794 samples were analyzed for dry matter (DM; method 930.15; AOAC Int., 2019) and for IDF and SDF (method 991.43; AOAC Int., 2019) using the AnkomTDF Dietary Fiber Analyzer (Ankom Technology, Macedon, NY, USA). Analyzed values for SDF, IDF, and TDF were corrected to 88% DM. Means for each ingredient were obtained using the UNIVARIATE procedure of SAS (SAS Stat Inc., Cary, NC, USA) and analyzed using the MIXED procedure of SAS, where the type of ingredient (i.e., cereal grains, cereal grain coproducts, oilseed coproducts) was the fixed effect. Results indicated that cereal grains on average contain 1.75 ± 1.62% SDF, 12.92 ± 7.76% IDF, and 14.67 ± 8.58% TDF, with the least TDF (2.78 ± 1.10%) obtained in rice and the greatest (35.06 ± 3.85%) in oats (Table 1). The SDF in cereal grain coproducts (1.95 ± 1.16%) was not different from cereal grains, but IDF and TDF (28.06 ± 18.63 and 29.98 ± 19.06%, respectively) were greater (P < 0.05) in cereal grain coproducts than in cereal grains, with the least TDF (7.47 ± 3.76%) being in corn gluten meal and the greatest (67.61 ± 5.01%) in oat hulls. Thus, cereal co-products contain more TDF than cereal grains because the fiber components are concentrated during processing. Oilseed coproducts contain more SDF (3.46 ± 1.71%; P < 0.05) than cereal grains and cereal grain coproducts and more (P < 0.05) IDF and TDF (28.48 ± 16.94 and 31.95 ± 18.02%, respectively) than cereal grains. Among oilseed coproducts, soybean hulls had the greatest TDF (67.8 ± 1.98%) and fermented soybean meal had the least (17.24 ± 1.51%). The greater concentration of SDF in oilseed co-products than in cereal grains and cereal grain coproducts demonstrate their potential to provide a readily fermentable substrate that may increase microbial activity and production of short-chain fatty acids, increase water retention, and increase the viscosity of the digesta. In conclusion, determining dietary fiber fractions as SDF, IDF, and TDF provides information about the fiber composition of feed ingredients, which may be used to determine and optimize nutritional strategies and promote the health and growth performance of animals.