Utilization of energy in high-fiber diets fed to pigs

Five experiments were conducted to investigate the utilization of energy in high-fiber diets fed to pigs. Experiment 1 determined the DE, ME, and NE of diets with 0, 15, or 30% wheat bran added to a corn-soybean meal-based diet fed to growing pigs. Indirect calorimetry also was used to determine O2 consumption and CO2 and CH4 production to calculate heat production by pigs. Results indicated that daily O2 consumption and CO2 and CH4 production by pigs fed increasing concentrations of wheat bran linearly decreased (P ≤ 0.05) resulting in a linear decrease (P ≤ 0.05) in heat production. The DE (3,454, 3,257, and 3,161 kcal/kg), ME (3,400, 3,209, and 3,091 kcal/kg), and NE (1,808, 1,575, and 1,458 kcal/kg) of diets decreased (P ≤ 0.05) linearly as wheat bran inclusion increased. Experiments 2 and 3 were conducted to determine effects of dietary fiber concentration and addition of a Bacillus-based direct-fed microbial (DFM) on wean-to-finish pigs. Results indicated that nursery pigs fed high-fiber diets had reduced (P ≤ 0.05) BW at the end of the nursery compared with nursery pigs fed low-fiber diets. This was because nursery pigs fed high-fiber diets had depressed (P ≤ 0.05) ADFI compared with nursery pigs fed low-fiber diets, indicating that diet bulk may be a hindrance to nursery pig feed intake. However, once pigs entered the grow-finish phase of the experiment (Exp. 3), high-fiber fed pigs experienced compensatory growth and, therefore, BW of high-fiber-fed pigs was not different compared with low-fiber-fed pigs at the end of the finisher. The addition of the Bacillus-based DFM to low- or high-fiber diets improved (P ≤ 0.05) G:F in nursery pigs. We hypothesized DFM addition would increase dietary fiber fermentation, thereby increasing VFA concentration and available energy; however, this was incorrect and we observed no effect of DFM supplementation on VFA concentration in the cecum or feces of nursery pigs. Results also indicated that pigs fed high-fiber diets had decreased (P ≤ 0.05) dressing percentage because weight of the large intestine was increased (P ≤ 0.05) compared with pigs fed low-fiber diets. The objective of Exp. 4 was to determine the effects of dietary fiber, a Bacillus-based DFM, and feeding duration on apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of nutrients and energy by growing pigs. Results indicated that AID of starch increased (P ≤ 0.05) as period (i. e., feeding duration) increased, regardless of diet type, which increased (P ≤ 0.05) ME as period increased. Contrary to our hypothesis, the ATTD of ADF or NDF was not increased as period increased. Addition of DFM to the low-fiber diet increased (P ≤ 0.05) the AID of ADF, NDF, Lys, Phe, and Glu. Experiment 5 was conducted to determine the disappearance of energy and dietary fiber fractions in the stomach and small intestine, cecum, and colon of pigs fed a corn-soybean meal basal diet or the basal plus distillers dried grains with solubles (DDGS), wheat middlings, or soybean hulls. The apparent cecal digestibility (ACD) and ATTD of soluble dietary fiber was not different among pigs fed experimental diets. Pigs fed the basal diet, or the basal diet plus wheat middlings, had greater (P ≤ 0.05) ACD of insoluble dietary fiber compared with pigs fed the basal diet plus DDGS or soybean hulls, whereas pigs fed the basal plus DDGS diet had greater (P ≤ 0.05) ACD of insoluble dietary fiber compared with pigs fed the basal plus soybean hulls diet. Wheat middlings had greater (P ≤ 0.05) disappearance of dietary fiber fractions compared with DDGS and soybean hulls. Physical characteristics of dietary fiber in experimental diets were not correlated with digestibility of nutrients and energy by pigs. In conclusion, utilization of energy by pigs fed high-fiber diets, especially diets with a substantial concentration of insoluble dietary fiber and a minimal concentration of soluble dietary fiber, was not improved because of increased dietary fiber digestibility or fermentability, but was improved by increased gastrointestinal tract weight that allowed for increased intake of a high-fiber diet