BACKGROUND
This study examined how adding wheat bran (WB), a fiber-rich ingredient, changes where and how nutrients are digested in pigs, and whether collecting ileal digesta before fecal sampling alters the total tract digestibility values measured afterward. The authors note that dietary fiber is known to increase endogenous nutrient losses and speed digesta passage, which generally lowers digestibility, but information on hindgut digestibility is limited. They also point out that in studies measuring both ileal and total tract digestibility, feces are usually collected before ileal digesta to avoid possible carryover effects, although this assumption had not been directly tested. The specific aim was therefore 2-fold: first, to determine the effects of graded WB inclusion on apparent ileal digestibility (AID), apparent total tract digestibility (ATTD), and hindgut digestibility (HD); second, to test whether ileal digesta collection influences proceeding fecal nutrient digestibility.
METHODS
Six crossbred barrows with an initial body weight of 70.7 kg (standard deviation = 5.7), each fitted with a T-cannula at the distal ileum, were used in a replicated 3 × 3 Latin square design with 3 dietary treatments and 3 periods. The basal diet was based mainly on wheat, soybean meal, and cornstarch. Two additional diets contained 20% or 40% WB in place of cornstarch. Soybean oil was adjusted to keep ether extract concentrations similar across diets, and all diets contained 0.5% chromic oxide as an indigestible index. Feed allowance was approximately 3% of body weight per day, divided into 2 meals at 0900 and 1700 h. Each experimental period included a 7-day adaptation period and a 4-day collection period. Fecal samples were collected for 24 h starting at 0900 h on day 8, ileal digesta were collected from 0930 to 1700 h on days 9 and 10, and another 24 h fecal collection started at 0900 h on day 11. Samples were analyzed for gross energy, dry matter (DM), crude protein (CP), ether extract (EE), amylase-treated neutral detergent fiber (aNDF), ash for organic matter (OM), calcium (Ca), phosphorus (P), and chromium. AID and ATTD were calculated using the chromium index method, and HD was calculated as ATTD minus AID. Statistical significance was declared at p-values less than 0.05, with tendency defined as p-values between 0.05 and 0.10.
KEY RESULTS
All pigs remained healthy and consumed their feed allotments, although 2 observations were missing because 2 pigs lost their cannula during the last period. With increasing WB from 0% to 40%, the AID of energy, DM, OM, CP, and P linearly decreased (p < 0.05). The ATTD of energy, DM, OM, CP, EE, and P also linearly decreased (p < 0.01) as WB increased. In contrast, the ATTD of aNDF linearly increased (p < 0.05). For hindgut digestion, the HD of DM and OM linearly increased (p < 0.05) with increasing WB. The abstract also states that hindgut digestibility of ether extract linearly increased (p < 0.05), whereas the Results section specifically mentions DM and OM; exact numerical digestibility coefficients were not clearly reported in the provided text. The paper’s conclusion summarizes the dietary fiber change as an increase in dietary aNDF from 4% to 20%, which reduced digestibility of energy and nutrients but increased hindgut digestibility of DM and OM. Regarding the methodological question, there was no interaction between fecal collection period and dietary treatment for ATTD of gross energy and nutrients. The ATTD of gross energy and most nutrients did not differ between fecal collections obtained before versus after ileal digesta collection. The only exception was that ATTD of OM tended to be less when fecal samples were collected after ileal digesta collection (p = 0.076). Regardless of collection period, the ATTD of gross energy, DM, OM, CP, EE, and P decreased (p < 0.01) as WB increased from 0% to 40%.
CLINICAL IMPLICATIONS
This is not a clinical human study, but it has practical implications for animal nutrition, digestive physiology, and the design of digestibility experiments in pigs. First, adding WB consistently reduced small-intestinal and total-tract availability of most nutrients, supporting the view that replacing highly digestible cornstarch with a fiber-rich ingredient lowers nutrient utilization. Second, some of the undigested material appears to be recovered through greater hindgut fermentation, particularly for DM and OM, indicating that high-fiber diets shift digestion distally rather than simply causing uniform nutrient loss throughout the gut. Third, the absence of a meaningful difference in ATTD between fecal collections taken before and after 2 days of ileal sampling suggests that short-term ileal digesta collection by T-cannula, conducted for 7.5 h per day, does not substantially disrupt subsequent fecal digestibility estimates. That finding supports common experimental practice and may reduce concern that ileal collection necessarily biases later total tract measurements. Overall, the study shows that increasing WB from 0% to 40% worsens ileal and total tract digestibility of several nutrients while increasing hindgut digestion of selected components, and it indicates that fecal digestibility measurements remain stable despite preceding ileal digesta collection under these study conditions.