Changing distillers grains: Implications for cattle performance and managemen

In the past decade, the ethanol industry has begun changing their production processes to capture more value from the corn kernel, altering the nutrient profile of distillers grains (DG). One of the first methods of value extraction includes partial removal of corn oil, resulting in a decreased oil or fat content of DG. Although the majority of ethanol plants are currently extracting oil from DG, limited research has been conducted regarding the use of new generation DG in finishing cattle diets. Previous research with decreased fat DG has shown varying results in cattle performance when compared to traditional DG. The inconsistency in performance results could be attributed to variation in oil extraction methods and thus, variation in the nutrient profile of new generation DG. Likewise, research evaluating the interaction of corn processing methods and decreased fat DG is limited. Therefore, this research was designed to determine: 1) if feeding moderate levels of wet DG (WDG) plus solubles (WDGS) would decrease the acidosis risk associated with further grain processing and allow fine grinding of corn to improve starch utilization and cattle performance and 2) the impact of feeding WDG produced from a novel cellulosic ethanol process for conversion of corn kernel fiber into cellulosic ethanol (C-WDG) on nutrient digestibility and feedlot performance of ruminants compared to traditional WDG (T-WDG). In experiment 1, it was hypothesized that because WDGS are low in starch concentration, increasing corn surface area would allow for improved starch digestibility while inclusion of WDGS would moderate the risk of acidosis. In diets containing 35% WDGS, apparent total starch digestibility was improved for steers fed finely ground corn (500 microns) compared to steers fed a traditional, dry-rolled corn (2350 microns). However, improved starch digestibility did not translate into improved performance with steers finished on finely ground corn having lighter final BW and decreased DMI and ADG. More recently, the ethanol industry is going beyond oil extraction moving towards fiber extraction. Therefore, a digestibility study utilizing lambs and a steer feedlot study to determine performance were designed to answer the second objective of this thesis. In the first experiment, DM digestibility was lesser in C-WDG compared to T-WDG at both the 30% and 45% inclusions of WDG. While NDF digestibility did not differ across treatments, ADF digestibility was not different between 30% T-WDG, 30% C-WDG, or 45% C-WDG. However, ADF digestibility was greater in lambs fed 45% T-WDG compared to other treatments, suggesting that the secondary fermentation process may be hindering the bioavailability of some portion of the remaining fiber in the C-WDG. In the performance study, steers fed T-WDG had similar final BW and ADG compared to C-WDG. However, steers fed C-WDG had an increased DMI and thus, less efficient G:F which could be explained by the differences in DM digestibility noted in the lamb study. Based on cattle performance, the estimated energy value of C-WDG was decreased by 25% compared to T-WDG. However, based on an economical simulation, the break-even price of C-WDG is similar to T-WDG when calculated based on cattle performance in this study. While digestibility was not evaluated, the addition of corn condensed distillers grains ( CCDS) to C-WDG in the feedlot trial resulted in similar feed efficiency while DMI and ADG were decreased compared to C-WDG-fed steers. In summary, new generation DG still added value to finishing diets compared to corn-based diets. These data suggest that feeding 35% WDGS when feeding finely ground corn results in increased starch utilization; however, additional research is needed to determine the optimal particle size and WDGS inclusion to maximize feedlot cattle performance. Furthermore, although WDG produced from secondary fermentation process for converting corn kernel fiber into cellulosic ethanol did result in decreased DM digestibility in lambs, final BW and ADG of steers were still similar to steers fed T-WDG. Overall, addition of new generation WDG in finishing diets maintained an advantage over a corn-based control diet based on cattle growth performance.