#13-014

Complete

Date Full Report Received

08/07/2015

Date Abstract Report Received

08/07/2015

Investigation

Institution:
Primary Investigator:
Co-Investigators: Pedro Urriola, Milena Saqui-Salces

Use of high fiber feed ingredients in commercial swine diets is a common strategy to decrease feed costs during times of high corn and soybean meal prices. However, the addition of high fiber feed ingredients to diets consistently results in a decrease in nutrient digestibility and subsequent decrease in energy and nutrient utilization efficiency. This reduction in feed efficiency is unpredictable using current methods to analyze dietary fiber such as neutral detergent fiber (NDF) or total dietary fiber (TDF). Therefore, the objective of this project was to develop and validate a “nutritional tool” to measure in vitro digestibility of fiber among high fiber feed ingredients, as well as measure changes in gut physiology and function of growing pigs fed diets with high concentration of different types of dietary fiber.

The most relevant high fiber feed ingredient used in North America are distillers dried grains with solubles (DDGS), which dietary fiber is highly insoluble. Therefore, for comparison we selected wheat straw (WS) and soybean hulls (SBH) as 2 other feed ingredients with high concentration of insoluble dietary fiber. We utilized an in vitro dry matter digestibility (IVDMD) assay that mimics gastric and small intestine hydrolysis (IVDMDh) and large intestine fermentation (IVDMDf) of pigs.

We observed differences in IVDMDh among WS (14.5%), SBH (19.7%), and DDGS (55.8%).We also observed differences in IVDMDf among WS (41.7%), SBH (68.5%), and DDGS (52.7%). These differences in IVDMDf were also in agreement with our data showing greater asymptotic gas production (A, mL/g DM substrate) for SBH (383.9) than DDGS (238.1) or WS (115.6). In addition to the differences among feed ingredients, we also observed a wide range of IVDMDh (45.3 to 63.2%) and IVDMDf (41.4 to 64.2%) among sources of corn DDGS.
To further test this technique, we fed growing pigs with 3 sources of WS, SBH, and DDGS with predicted low, medium, and high IVDMDf. We observed that apparent total tract digestibility (ATTD) of TDF was least in WS (26.7%), intermediate for DDGS (43.0%), and greatest in SBH (78.9%). These observations were in agreement with predictions from the in vitro gas production results, and suggest that this in vitro gas production technique is a reliable procedure to measure ATTD of TDF.
An additional objective was to measure the impact of insoluble dietary fiber on gut function (digestion of nutrients), morphology (cell proliferation), and immunity. We observed that feeding feed ingredients with insoluble dietary fiber (WS, SBH, and DDGS) to growing pigs modified morphology of the gut, the composition of the cells, and the balance among immune cells. In pigs fed the WS diet, the area of the gut occupied by mucus producing (goblet) cells was increased in comparison with pigs fed DDGS and SBH diets. However, DDGS caused greater proliferation of all cells. This greater proliferation index is consistent with greater number of enterocytes observed from measuring the fatty acid binding protein (FABP) marker. Finally, feeding all 3 sources of insoluble dietary fiber (WS, DDGS, and SBH) to growing pigs decrease the ratio between pro-inflammatory markers (IL10) and anti-inflammatory markers (IL-12) compared with corn-soybean meal diets.
In conclusion, we observed that large differences exist in ATTD of TDF among sources high fiber feed ingredients. Fortunately, these differences in ATTD of TDF among high fiber feed ingredients can be reasonably predicted in vitro by simulation of gastric and small intestine hydrolysis and large intestine fermentation and gas production. Additionally, dietary fiber from these feed ingredients affects gut physiology and function in different fashion that it is not predicted by the concentration of TDF or NDF in the diet. Therefore, more detailed information on the carbohydrate structure and interaction with the gut epithelium is necessary to improve utilization of high fiber feed ingredients fed to growing pigs.
Key Findings:
• Digestibility of dietary fiber affects the concentration of metabolizable energy among sources of corn DDGS
• In vitro procedures can be used to measure digestibility and fermentability of fiber among sources of corn DDGS
• Our results are the first to show that there are differences in goblet cells and mucin production among pigs fed diets with insoluble dietary fiber, which suggests that the effect of dietary fiber on gut physiology and function is not only related to the concentration of fiber in the diet (TDF or NDF), but also to the botanical origin of the dietary fiber.
• Feeding feed ingredients with insoluble dietary fiber (WS, SBH, and DDGS) to growing pigs modified morphology of the gut, the composition of the cells, and the balance among immune cells, which will guide future experiments to develop feed formulation and feeding strategies to optimize fiber use in swine diets.