Application of feed processing methods and use of exogenous feed additives in an effort to improve nutrient digestibility of plant-based feed ingredients for swine has been studied for decades. The following review will discuss several of these topics, including: fiber characterization, impact of dietary fiber on gastrointestinal physiology, energy, and nutrient digestibility, mechanical processing of feed on fiber and energy digestibility, and the use of exogenous enzymes in diets fed to growing pigs. Taken together, the diversity and concentration of chemical characteristics that exists among plant-based feed ingredients, as well as interactions among constituents within feed ingredients and diets, suggests that improvements in nutrient digestibility and pig performance from mechanical processing or adding exogenous enzymes to diets fed to swine depends on a better understanding of these characteristics, but also relating enzyme activity to targeted substrates. It may be that an enzyme must not only match a target substrate(s), but there may also need to be a ′cocktail′ of enzymes to effectively breakdown the complex matrixes of fibrous carbohydrates, such that the negative impact of these compounds on nutrient digestibility or voluntary feed intake are alleviated. With the inverse relationship between fiber content and energy digestibility being well described for several feed ingredients, it is only logical that development of processing techniques or enzymes that degrade fiber, and thereby improve energy digestibility or voluntary feed intake, will be both metabolically and economically beneficial to pork production.

In livestock diets, energy is one of the most expensive nutritional components of feed formulation. Because lipids are a concentrated energy source, inclusion of lipids are known to affect growth rate and feed efficiency, but are also known to affect diet palatability, feed dustiness, and pellet quality. In reviewing the literature, the majority of research studies conducted on the subject of lipids have focused mainly on the effects of feeding presumably high quality lipids on growth performance, digestion, and metabolism in young animals. There is, however, the wide array of composition and quality differences among lipid sources available to the animal industry making it essential to understand differences in lipid composition and quality factors affecting their digestion and metabolism more fully. In addition there is often confusion in lipid nomenclature, measuring lipid content and composition, and evaluating quality factors necessary to understand the true feeding value to animals. Lastly, advances in understanding lipid digestion, post-absorption metabolism, and physiological processes (e.g., cell division and differentiation, immune function and inflammation); and in metabolic oxidative stress in the animal and lipid peroxidation, necessitates a more compressive assessment of factors affecting the value of lipid supplementation to livestock diets. The following review provides insight into lipid classification, digestion and absorption, lipid peroxidation indices, lipid quality and nutritional value, and antioxidants in growing pigs.

Twenty corn coproducts from various wet- and dry-grind ethanol plants were fed to finishing pigs to determine DE and ME and to generate equations predicting DE and ME based on chemical analysis. A basal diet comprised corn (97.05%), limestone, dicalcium phosphate, salt, vitamins, and trace minerals. Twenty test diets were formulated by mixing the basal diet with 30% of a coproduct, except for dried corn solubles and corn oil, which were included at 20 and 10%, respectively. There were 8 groups of 24 finishing gilts (n = 192; BW = 112.7 ± 7.9 kg). Within each group, gilts were randomly assigned to 1 of 5 test diets or the basal diet for a total of 4 replications per diet per group. Two groups of gilts were used for each set of coproducts, resulting in 8 replications per coproduct and 32 replications of the basal diet. The experiment was conducted as a completely randomized design. Gilts were placed in metabolism crates and offered 3 kg daily of their assigned test diet for 13 d, with total collection of feces and urine during the last 4 d. Ingredients were analyzed for DM, GE, CP, ether extract, crude fiber, NDF, ADF, total dietary fiber (TDF), ash, AA, and minerals, and in vitro OM digestibility was calculated for each ingredient. The GE was determined in the diets, feces, and urine to calculate DE and ME for each ingredient. The DE and ME of the basal diet were used as covariates among groups of pigs. The DE of the coproducts ranged from 2,517 kcal/kg of DM (corn gluten feed) to 8,988 kcal/kg of DM (corn oil), and ME ranged from 2,334 kcal/kg of DM (corn gluten feed) to 8,755 kcal/kg of DM (corn oil). By excluding corn oil and corn starch from the stepwise regression analysis, a series of DE and ME prediction equations were generated. The best fit equations were as follows: DE, kcal/kg of DM = −7,471 + (1.94 × GE) − (50.91 × ether extract) + (15.20 × total starch) + (18.04 × OM digestibility), with R² = 0.90, SE = 227, and P < 0.01; ME, kcal/kg of DM = (0.90 × GE) − (29.95 × TDF), with R² = 0.72, SE = 323, and P < 0.01. Additional equations for DE and ME included NDF in the instance that TDF data were not available. These results indicate that DE and ME varied substantially among corn coproducts and that various nutritional components can be used to accurately predict DE and ME in corn coproducts for finishing pigs. Copyright © 2012. American Society of Animal Science .

Feed fats and oils provide significant amounts of energy to swine diets, but there is large variation in composition, quality, feeding value, and price among sources. Common measures of lipid quality include moisture, insolubles, and unsaponifiables (MIU), titer, and free fatty acid content, but provide limited information regarding their feeding value. Lipid peroxidation is an important quality factor related to animal growth performance and health, but maximum tolerable limits in various lipids have not been established. Several indicative assays can be used to detect the presence of various peroxidation compounds, but due to the complexity and numerous compounds produced and degraded during peroxidation process, no single method can adequately determine the extent of peroxidation. Until further information is available, using a combination of peroxide value, thiobarbituric acid reactive substances (TBARS), and anisidine value appear to provide a reasonable assessment of the extent of peroxidation in a lipid at a reasonable cost. However, fatty acid composition of the lipid being evaluated should be considered when selecting specific assays. Predictive tests can also be used to estimate the stability or susceptibility of lipids to peroxidation and include active oxygen method, oil stability index, and oxygen bomb method. A review of 16 published studies with pigs has shown an average decrease of 11.4% in growth rate, 8.8% feed intake fed isocaloric diets containing peroxidized lipids compared to diets containing unperoxidized lipids of the same source. Furthermore, serum vitamin E content was generally reduced and serum TBARS content was increased when peroxidized lipids were fed in these studies, suggesting that feeding peroxidized lipids negatively affects metabolic oxidative status of pigs. However, it is unclear if antioxidants are useful additions to lipids to maintain optimal nutritional value, or if their addition to swine diets is beneficial in overcoming a metabolic oxidative challenge.

The apparent DE and ME values of crude glycerol for growing pigs were determined in 5 experiments using crude glycerol (86.95% glycerol) from a biodiesel production facility, which used soybean oil as the initial feedstock. Dietary treatments were 0, 5, or 10% glycerol addition to basal diets in Exp. 1; 0, 5, 10, or 20% glycerol addition to basal diets in Exp. 2; and 0 and 10% crude glycerol addition to the basal diets in Exp. 3, 4, and 5. Each diet was fed twice daily to pigs in individual metabolism crates. After a 10-d adjustment period, a 5-d balance trial was conducted. During the collection period, feces and urine were collected separately after each meal and stored at 0°C until analyses. The GE of each dietary treatment and samples of urine and feces from each pig were determined by isoperibol bomb calorimetry. Digestible energy of the diet was calculated by subtracting fecal energy from the GE in the feed, whereas ME was calculated by subtracting the urinary energy from DE. The DE and ME values of crude glycerol were estimated as the slope of the linear relationship between either DE or ME intake from the experimental diet and feed intake. Among all experiments, the crude glycerol (86.95% glycerol) examined in this study was shown to have a DE of 3,344 ± 8 kcal/kg and an ME of 3,207 ± 10 kcal/kg, thereby providing a highly available energy source for growing pigs. Copyright © 2008. . Copyright 2008 Journal of Animal Science

Two experiments were conducted to determine the DE and ME content of corn distillers dried grains with solubles (corn-DDGS) containing variable ether extract (EE) concentrations and to develop DE and ME prediction equations based on chemical composition. Ether extract content of corn-DDGS ranged from 4.88 to 10.88% (DM basis) among 4 corn-DDGS samples in Exp. 1 and from 8.56 to 13.23% (DM basis) among 11 corn-DDGS samples in Exp. 2. The difference in concentration of total dietary fiber (TDF) and NDF among the 4 corn-DDGS sources was 2.25 and 3.40 percentage units, respectively, in Exp. 1 but was greater among the 11 corn-DDGS sources evaluated in Exp. 2, where they differed by 6.46 and 15.18 percentage units, respectively. The range in CP and ash were from 28.97 to 31.19% and 5.37 to 6.14%, respectively, in Exp. 1 and from 27.69 to 32.93% and 4.32 to 5.31%, respectively, in Exp. 2. Gross energy content among corn-DDGS samples varied from 4,780 to 5,113 kcal/kg DM in Exp. 1 and from 4,897 to 5,167 kcal/kg DM in Exp. 2. In Exp. 1, the range in DE content was from 3,500 to 3,870 kcal/kg DM and ME content varied from 3,266 to 3,696 kcal/kg DM. There were no differences in ME:DE content among the 4 corn-DDGS sources in Exp. 1, but ME:GE content differed (P = 0.04) among sources (66.82 to 74.56%). In Exp. 2, the range in DE content among the 11 corn-DDGS sources was from 3,474 to 3,807 kcal/kg DM and ME content varied from 3,277 to 3,603 kcal/kg DM. However, there were no differences in DE:GE, ME:DE, or ME:GE among sources in Exp. 2. In Exp. 1, no ingredient physical or chemical measurement [bulk density (BD), particle size, GE, CP, starch, TDF, NDF, ADF, hemicellulose, EE, or ash)] was statistically significant at P ≤ 0.15 to predict DE or ME content in corn-DDGS. In Exp. 2, the best fit DE equation was DE (kcal/kg DM) = 1,601 – (54.48 × % TDF) + (0.69 × % GE) + (731.5 × BD) [R² = 0.91, SE = 41.25]. The best fit ME equation was ME (kcal/kg DM) = 4,558 + (52.26 × % EE) – (50.08 × % TDF) [R² = 0.85, SE = 48.74]. Apparent total tract digestibility of several nutritional components such as ADF, EE, and N were quite variable among corn-DDGS sources in both experiments. These results indicate that although EE may be a good predictor of GE content in corn-DDGS, it is not a primary factor for predicting DE or ME content. Measures of dietary fiber, such as ADF or TDF, are more important than EE in determining the DE or ME content of corn-DDGS for growing pigs. Copyright © 2013. American Society of Animal Science .