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J. Anim. Sci. 2002. 80:2629-2638
© 2002 American Society of Animal Science

The nutritional value of degermed, dehulled corn for pigs and its impact on the gastrointestinal tract and nutrient excretion

A. J. Moeser*, I. B. Kim{dagger}, E. van Heugten* and T. A. T. G. Kempen*,1

* Department of Animal Science, North Carolina State University, Raleigh 27695 and and {dagger} SunJin Co., Ltd., SunJin B/D 2F, # 517-8, Doonchon-Dong, Kangdong-Gu, Seoul 134-060, Korea

1 Correspondence:
phone 919-515-4016; fax: 919-515-7780; E-mail:
t_vankempen{at}ncsu.edu.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
Three experiments were designed to assess the feeding value and potential environmental benefits of feeding degermed, dehulled corn, a low fiber by-product originating from the corn dry milling process, to pigs. Twelve 27-kg (SE = 0.8) barrows were used in Exp. 1 to measure the apparent fecal digestibility of DM, GE and N of degermed, dehulled corn compared with corn grain. Two diets were formulated to contain either 96.4% of degermed, dehulled corn or corn grain plus supplemental vitamins and minerals. Digestibilities of DM, GE, and N were greater in degermed, dehulled corn (96.2, 96.0, and 93.6%, respectively) compared with corn grain (89.0, 89.0, and 78.4%, respectively) (P < 0.01). Overall, a 67 and 29% reduction in DM and N excretion, respectively, was observed. In Exp. 2, eight 70-kg (SE =1.8) barrows were surgically fitted with ileal cannulae and fed the same diets as in Exp. 1, to measure the ileal digestibility of nutrients in degermed, dehulled corn. Ileal digestibility of DM, energy, and N was 13, 15, and 7% greater in degermed, dehulled corn (P < 0.05). Apparent ileal digestibility coefficients of leucine, methionine, and phenylalanine were greater in degermed, dehulled corn compared with corn grain (P < 0.05) while a trend for a lower tryptophan digestibility in degermed, dehulled corn was observed (P = 0.067). In Experiment 3, 96 nursery pigs with an initial average BW of 8.8 kg (SE = 0.08), fed a starter diet formulated with degermed, dehulled corn or corn grain as the major grain source, were used in a 28-d growth performance study. At the end of the study, 24 pigs (1 pig per pen) were sacrificed and gastrointestinal tract measurements were taken. Daily growth rates of pigs were the same between diets (0.64 kg/d). A trend for reduced feed intake (P = 0.073) in pigs fed degermed, dehulled corn led to a 4% improvement in gain to feed (P < 0.05). Feeding degermed, dehulled corn had no effect on gut fill, gastrointestinal tract weight, or liver weight (P > 0.05). Ileal villus lengths and crypt depths were not affected by feeding degermed, dehulled corn although ileal villus widths were greater in pigs fed corn grain. Results from these trials suggest that corn processed to remove poorly digestible fiber fractions provides more digestible nutrients than corn grain. As a result, degermed, dehulled corn reduces fecal and N excretion, thus providing a means to reduce nutrient excretion.

Key Words: Digestibility • Maize • Nutrients • Pigs


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 
Dietary fiber negatively impacts energy and nutrient utilization by swine and as a consequence, increases waste production and nutrient excretion (Shi and Noblet., 1994; Canh et al., 1998; Davidson and McDonald, 1998). Although the fiber content in a standard U.S. corn-soybean meal diet is considered to be relatively low (approximately 9% NDF), any means to further reduce this fiber would improve the overall nutritional value of the diet. Corn, due to its high inclusion level in swine diets, contributes approximately 70% of the dietary fiber content in a typical corn-soybean meal diet. The fiber in the corn kernel, as with most other cereal grains, is predominantly located in the hull and germ fractions of the kernel. The hull fraction makes up approximately 5% of the total kernel weight and contributes 51% of the total kernel fiber while the germ fraction makes up 11% of the kernel weight and contributes 16% of the total kernel fiber (Watson, 1987). Therefore, removal of these fiber-rich corn fractions should have a significant impact on the nutrient composition of corn and potentially enhance the nutritional value of corn.

Degermed, dehulled corn is a product of the corn dry milling processes in which the germ and hull fraction of the kernel have been removed, thus yielding a potentially low-fiber swine feed ingredient. The objectives of this research were to assess the nutritional value of degermed, dehulled corn, its effect on the gastrointestinal tract of swine, and its effect on nutrient excretion.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results and Discussion
 Implications
 Literature Cited
 
All animal protocols were approved by the North Carolina State University Animal Care and Use Committee (IACUC).

Experiment 1.
Twelve crossbred barrows with an initial average BW of 27 kg (SE = 0.8) were used to determine the apparent fecal digestibility and balance of GE and N in degermed, dehulled corn compared with corn grain. Two diets were formulated to contain either 96.4% corn grain (control) or degermed, dehulled corn and 3.4% vitamins and minerals (Table 1Go). Vitamins and minerals were supplied to meet or exceed requirements for 20 to 40 kg pigs (NRC, 1998). Diets were formulated such that each corn product (corn grain or degermed, dehulled corn) was the sole source of protein and energy. The two diets were assigned to 12 barrows according to a randomized complete block design based on initial body weight. Pigs were housed in metabolism cages (1.5 x 2.0 m) and given ad libitum access to water.


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  		Table 1. Ingredients used in Exp. 1 and 2, g/kg as fed basis
 
Pigs were fed experimental diets twice daily (0800 and 1500) in mash form at a feeding level equal to 90 g/kg body weight0.75. The metabolism study consisted of two 9-d periods, each including a 5-d dietary adaptation period followed by a 4-d quantitative collection of feces and urine. Feces were collected twice daily, weighed, and pooled for individual pigs and stored at -20°C until subsequent sample preparation for chemical analysis. Urine was collected twice daily in plastic buckets to which 10 mL of 70% sulfuric acid was added. Urine volume was measured daily, composited, and stored at -20°C until subsequent chemical analyses.

Experiment 2.
Eight crossbred barrows with an initial average BW of 70 kg (SE = 1.8), surgically fitted with simple-T ileal cannulae, were used to measure the ileal digestibility of DM, GE, and amino acids in degermed, dehulled corn compared with corn grain. Prior to surgery, feed was withheld from pigs for 36 h. Each cannula was introduced into the distal ileum according to the procedures adapted from Sauer et al. (1983). During the post-operative period of 14 d, animals were given ad libitum access to a commercial diet. Pigs were given ad libitum access to water before and after surgery.

Diets and feeding procedures were identical to those described in Exp. 1 except that 0.3% chromic oxide was added as an inert digestibility marker, and a different batch of degermed, dehulled corn was used. Animals were housed in concrete, smooth-walled pens (1.5 x 1.0 m). At the start of the experiment, pigs were blocked by weight and assigned to test diets. The experiment was conducted according to a cross-over design that consisted of two 7-d periods each with a 5-d dietary adaptation period followed by a 2-d collection period. During the collection period, ileal digesta was collected continuously each day over a 12-h period (from 0800 to 2000) from the cannulae into an attached 125-mL, Nalgene plastic bottle (Rochester, NY). Upon collection, ileal digesta was immediately frozen at -20°C. The collected digesta samples were pooled by animal and by period for subsequent chemical analyses.

Experiment 3.
Ninety-six nursery pigs (48 barrows and 48 gilts) with an initial average BW of 8.8 kg (SE = 0.08) were used to evaluate the impact of dietary inclusion of degermed, dehulled corn in nursery pig diets on growth performance and gastrointestinal tract characteristics. At 21 d of age, pigs were weaned and transferred to nursery pens (1.73 m x 0.83 m), with four pigs per pen, and fed a commercial starter ration (3,662 kcal of DE, 1.4% lysine) for 2 wk. Following the adjustment, pigs were weighed, blocked by sex and weight, and assigned to the experimental diets. Diets were formulated to contain either degermed, dehulled corn or corn grain as the major grain source equal to 56.2 and 58.5% of the diet, respectively. Diets were formulated to contain identical ME and ileal digestibility values for degermed, dehulled corn measured in Exp. 1 and 2 (Table 2Go). Body weight and feed disappearance were measured on d 7, 14, 21, and 28 of the 4-wk growth performance trial. Water and feed were offered on an ad libitum basis.


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  		Table 2. Composition of diets used in Exp. 3, g/kg as fed basis
 
Following the 28-d performance trial, 24 pigs (randomly selected; 12 pigs per dietary treatment; 1 pig per pen) were humanely killed according to approved electrocution and exsanguination procedures (FASS, 1999). Visceral organs (liver, pancreas, and intestines) and stomach were weighed immediately after evisceration, and empty body weight was determined as body weight minus viscera. Weights of the full gastrointestinal tract, empty gastrointestinal tract, and liver were also recorded. Gut fill was determined by subtracting the empty gastrointestinal tract weight from the full gastrointestinal tract weight. The small intestine was dissected from the stomach, duodenum, and mesentery and laid out in 60-cm loops, and the midpoint of the small intestine was marked. Ileal tissue for histology was harvested by using the midpoint of the small intestine as an anatomical landmark and obtaining a 3-cm cross section of intestine halfway between the midpoint of the small intestine and posterior ileum (designating the ileum). Intestinal segments were gently stripped of digesta and immediately submerged into phosphate buffer solution (PBS, pH 7.4) on ice for approximately 5 min. Each intestinal segment was then fixed in fresh fixative solution (FEA: formalin, 95% ethanol, and glacial acetic acid solution) for 24 h. After 24 h, fixative solution was replaced by 70% ethanol and stored at room temperature until they were embedded in paraffin as previously described by Luna (1968).

Chemical Analysis
The DM content of the corn products (corn grain and degermed, dehulled corn) and feces was determined by drying samples to a constant weight in an oven at 60°C. Dried samples were then ground through a 1-mm screen in a Retsch® mill (model ZM 100; Haan, Germany) before chemical analysis. Feed and fecal samples were then analyzed in duplicate for GE content using an adiabatic bomb calorimeter (model C5000; IKA, Wilmington, NC). Nitrogen content of corn products, feces, and urine was assayed by the Kjeldahl method, and crude protein was calculated as Kjeldahl-N x 6.25 (AOAC, 1990). Analysis of amino acid and chromium levels in the diets and ileal digesta in Exp. 2 was performed in accordance with AOAC (1990) procedures by the Experimental Station Chemical Laboratories (University of Missouri-Columbia, MO). Neutral detergent fiber and ADF of corn samples and diets were analyzed nonsequentially using a modified version of the Van Soest method for fiber analysis (Van Soest, 1967) developed by Ankom Technologies (Fairport, NY) in which sealed fiber bags were refluxed in detergent solutions. Heat-stable alpha-amylase (activity range — 340,000 to 375,000 modified wohlgemuth units per mL) was added at a rate of 0.5 mL per sample to degrade the remaining starch.

Calculations and Statistical Analysis
All data were subjected to analysis of variance using the ANOVA procedure of SAS (version 8.1, Cary, NC). Pen, animal, and diet effects were included in the statistical models for Exp. 1 and 2 and for the gastrointestinal tract data in Exp. 3. The model for growth performance data in Exp. 3 included pen, diet, block, and sex. Values were considered statistically different when a treatment effect with a P < 0.05 was observed (Steel and Torrie, 1980).


   Results and Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
Implications
 Literature Cited
 
Production of Degermed, Dehulled Corn Through the Dry Milling Process
Corn dry milling represents approximately 20% of the corn grain processing in the United States. Although the main objective of dry milling is to produce flaking grits for use in human foods, several by-products are yielded in the process that can be used for human or animal consumption. Dry milling of corn involves a series of steps that are designed to physically separate the corn kernel into its anatomical constituents (endosperm, hull, and germ). The first step of the dry milling process requires the addition of dilute sulfuric acid to whole corn kernels in a tempering bin which serves to increase the moisture content of the kernel (to approximately 20%) and thus increases the resiliency of the germ in the subsequent degerming processes. The tempered corn is then processed through a Beal Degerminator, which strips the hull and germ away from the kernel by an abrading action leaving mainly intact endosperm material. A series of steps follow to separate the hull and germ fractions from the endosperm material. The germ and hull fractions separated in these steps are typically sold as animal feed ingredients whereas the endosperm material is further separated by a series of size separation steps to produce endosperm particles of different sizes. The larger endosperm particles are used for the production of flaking grits. Degermed, dehulled corn is derived from the remaining, smaller fractions of endosperm which are sent through roller mills for further reduction in particle sizes, yielding human food products such as brewers grits and corn meals for bakery and snack foods (Alexander, 1987).

Analyzed Nutrient Composition of Degermed, Dehulled Corn
Analyzed levels of nutrients in the corn products tested are presented in Table 3Go. The sample lots of corn grain and degermed, dehulled corn used in Exp. 1 were not from the same batch as the material used in Exp. 2 and 3, and therefore, nutrient compositions are reported separately within each experiment.


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  		Table 3. Nutrient composition of degermed, dehulled corn compared with corn grain, dry matter basis
 
Gross energy contents were lower in the degermed, dehulled corn compared with corn grain which most likely reflects the removal of the germ fraction from the kernel. The germ fraction of the corn kernel is the primary depository for oil (accounting for approximately 83% of the oil in the corn kernel) and, therefore, a reduction in GE content is expected (Earle, 1977). In comparison with NRC (1998) values for the protein content of ground corn grain (9.3% protein), degermed, dehulled corn samples were lower in protein content. Given that the germ contains 26% of the total kernel protein, it can be expected that the physical removal of this fraction will result in a reduction in protein content as observed in this experiment. It should be noted that the corn grain used in Exp. 1 had a low-protein content (lower than degermed, dehulled corn).

Only the corn products used in Exp. 2 and 3 were analyzed for their essential amino acid concentrations. With the exception of the amino acids methionine and tryptophan, all essential amino acids were lower in degermed, dehulled corn compared with corn grain. It is noteworthy that the most limiting amino acid lysine was 33% lower in degermed, dehulled corn compared with corn grain. This reduction in lysine content is in line with expectations as degermed, dehulled corn is mainly endosperm material in which the protein is in the form of insoluble zein proteins which are known to be lysine deficient (Wilson, 1987). On the other hand, the protein in the germ is composed mainly of albumins (35% of germ protein) and globulins (18% of germ protein), which are particularly rich in lysine compared with the endosperm fraction. Analyzed NDF and ADF contents in degermed, dehulled corn were notably lower compared with the corn grain with 61 and 32% less NDF and ADF, respectively, in degermed, dehulled corn. Although the hull of the corn kernel represents only 5% of the total kernel weight, it contributes approximately 51% of the kernel fiber. In addition, the germ fraction contributes approximately 16% of the total kernel fiber explaining the large difference in fiber content observed between the corn products (Watson, 1987).

Experiment 1. Apparent Fecal Digestibility and Balance of Energy and Nitrogen in Degermed, Dehulled Corn
Fecal digestibility of DM and energy was 8% greater in degermed, dehulled corn compared with corn grain (Table 4Go). As a result, DE contents of degermed, dehulled corn was approximately 100 kcal/kg greater compared with corn grain (3,564 and 3,464 kcal/kg for degermed, dehulled corn and corn grain, respectively). The metabolizability of energy, reported as a percentage of energy intake, followed a similar pattern as energy digestibility with an 8% improvement in the metabolizability of degermed, dehulled corn over corn grain.


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  		Table 4. Energy and N balance of degermed, dehulled corn in Exp. 1a
 
As illustrated in Table 3Go, the NDF content in degermed, dehulled corn was approximately six percentage units lower compared with corn grain. Assuming a linear relationship between the NDF content in corn and energy digestibility, this equates to a 1.2% improvement in energy digestibility for each 1% decrease in NDF content. This is in agreement with Just et al. (1983) who reported a 1.3 and 0.9% increase in energy digestibility and metabolizability, respectively, for each 1% reduction in dietary fiber content. Noblet and Perez (1993) reported similar results with grower pigs with each 1% decrease in dietary fiber resulting in an improvement in energy digestibility by 1.1%.

Nitrogen intakes were greater in pigs fed degermed, dehulled corn due to the higher protein content in the degermed, dehulled corn used in this experiment (P < 0.05). Improvements in the digestibility (by 19%) and retention of N (by 20%) were observed in degermed, dehulled corn compared with corn grain (P < 0.001). Although our N retention values are comparable with published values (Adeola and Bajjalieh, 1997; Veum et al., 2001) for corn and(or) corn-based diets for pigs, they appear to be surprisingly high irrespective of the corn feedstuff. In our study, diets contained 96.4% of corn grain or degermed, dehulled corn and therefore were not formulated to meet the essential amino acid requirements of grower pigs. Typically, N balance data from pigs fed commercial feedstuffs range between 30 to 55% retention as a percentage of N intake (NRC, 1998). In this study, N retention values were approximately 59 and 71% of N intake for corn grain and degermed, dehulled corn, respectively. This implies that certain experimental procedures, namely the urine collection, may result in excessive N loss as ammonia prior to acidification thereby inflating N retention data.

Experiment 2. Apparent Ileal Digestibility of Nutrients in Degermed, Dehulled Corn
In line with data on apparent fecal digestibility, apparent ileal digestibility of DM, energy, and N were 13, 15, and 7% greater (P < 0.05), respectively, in degermed, dehulled corn compared with corn grain.

Apparent ileal digestibility coefficients of leucine, methionine, and phenylalanine were greater in degermed, dehulled corn compared with corn grain (P < 0.05) while a trend for a lower tryptophan digestibility in degermed, dehulled corn was observed (P = 0.07). It should be noted that the reporting of ileal amino acid digestibility coefficients on an apparent basis in this study confounds results as apparent digestibility coefficients are affected by the amino acid content of the test diet (Li et al.,1993; Fan et al., 1994). In this sense, ileal digestibility data presented on a standardized basis (correcting for basal endogenous N secretions) would provide more relevant data (Stein et al., 2001). However, basal endogenous losses were not directly measured from pigs in this study, and therefore standardized digestibility coefficients were not included in Table 5Go. Using the data of Tran et al. (1999) to correct for basal endogenous losses, it was observed that the standardized ileal digestibility coefficients of all essential amino acids (with the exception of histidine, tryptophan, and threonine) were greater (P < 0.05) in degermed, dehulled corn compared with corn grain (data not shown). The greatest improvement was in the first limiting amino acid in a corn-soybean meal diet for swine, lysine, in which a 10% improvement in the standardized ileal digestibility of degermed, dehulled corn over corn grain was observed.


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  		Table 5. Apparent ileal digestibility of nutrients in degermed, dehulled corn and corn grain in Exp. 2a
 
Improvements in the ileal digestibility of amino acids in degermed, dehulled corn in this study can be explained by the low fiber content it possesses. Fiber has been shown to have diverse physiological and chemical activities in the small intestine of pigs and can impair the digestion and absorption of amino acids from both exogenous and endogenous origin. Digestive secretions from gastric, biliary, and pancreatic origin are increased when fiber is added to pig diets (Dierick et al., 1989; Low, 1989). These secretions represent endogenous N losses and are a result of the direct stimulation of fiber on the digestive secretions (Langlois et al., 1987) and the impaired absorption of secreted protein and amino acids in the presence of dietary fiber (Bergner et al., 1981). Jørgensen et al. (1996) reported a reduced ileal N digestibility in a high-fiber diet (26.8% dietary fiber) compared with a low-fiber diet (5.9% dietary fiber). Lenis et al. (1996) also reported reductions in ileal N digestibility when supplementing a purified basal diet with a purified source of fiber.

As mentioned previously, due to the removal of the germ fraction of the corn kernel in degermed, dehulled corn, a significant reduction in total lysine content (by 33%) was noted. However, standardized ileal digestibility was increased by 10% in degermed, dehulled corn. The net result was that degermed, dehulled corn and corn grain yielded approximately 1.5 and 2.1 g of digestible lysine per kg of DM intake, respectively (data not shown). Practically, this implies that additional lysine will have to be supplied to overcome this difference when formulating degermed, dehulled corn into swine diets.

Experiment 3. Effects of Degermed, Dehulled Corn on Growth Performance and Gastrointestinal Tract Characteristics of Nursery Pigs
Inclusion of degermed, dehulled corn as the major grain source in nursery pig diets had no effect on average daily gain (Table 6Go). However, pigs fed the degermed, dehulled corn diet tended to consume less feed than pigs fed the control (P = 0.091) resulting in a 4% improvement in gain to feed (P < 0.05).


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  		Table 6. Performance of pigs fed diets containing corn grain or degermed, dehulled corn in Exp. 3a
 
There are no directly comparable studies in the literature that study the effects of processing corn to remove the indigestible fiber content and its subsequent effect on animal performance. In general, growth rate and feed efficiency in pigs are reduced as the dietary fiber level is increased (Kass et al., 1980). Several mechanisms account for this phenomenon. Foremost, dietary fiber serves to dilute the dietary energy content. However, in some situations, especially in the older pig, this reduction in DE content can be compensated for by increasing feed intake given that the fiber level does not exceed 10 to 15% of the diet or cause any unpalatability or bulkiness problems (NRC, 1998). The energetic efficiency of absorbed VFA resulting from microbial fermentation of fiber in the large intestine may also explain the negative impact of fiber on growth due to the fact that energy utilization from VFA is less efficient compared with glucose absorption in the small intestine (Grieshop et al., 2001). Other factors involved in the growth-depressing effects of feeding pigs a high-fiber diet include dietary fiber-mineral interactions, reduced N utilization, and increased rates of passage (Calvert, 1988).

Dietary fiber content can significantly impact the gastrointestinal tract development and consequently alter energy metabolism. In general, the weight and volume of the gastrointestinal tract and associated visceral organs have been shown to increase in response to feeding higher levels of fiber (Coey and Robinson, 1954; Southgate, 1990; Hansen et al., 1992). Relative to their size, visceral organs have a disproportionately high rate of energy expenditure. Therefore, it is believed that the relative changes in organ size induced by high-fiber feeding may have a significant impact on energy metabolism and the efficiency of growth (Pekas and Wray, 1991). This was illustrated by Yen et al. (1989), who found that organs drained by the hepatic-portal vein (including the large intestine) consumed approximately 25% of the whole body maintenance requirement (expressed as O2 consumption) despite representing less than 4% of total body weight. It seems plausible that lowering dietary fiber content, via inclusion of degermed, dehulled corn, would result in a partitioning of dietary energy to growth rather than supporting increased digestive enzyme synthesis and visceral hypertrophy. However, lowering dietary fiber via inclusion of degermed, dehulled corn in this current study had no effect (P > 0.05) on the hypertrophy of the visceral organs (Table 7Go). It can be noted that numerical differences were observed with regards to increased gut fill, total gastrointestinal tract weight, and liver weight. However, our inability to detect any significant differences between dietary treatments may be due to the level of dietary fiber in this study. In the literature, studies (Anugwa et al., 1989; Hansen et al., 1992; Jorgensen et al., 1996) reporting significant effects of dietary fiber on the hypertrophy of the gastrointestinal tract used diets containing high levels of dietary fiber content (ranging between 20 to 40% dietary NDF), whereas in our study, the control diet contained only 6.7% NDF. In addition, the extent or short duration of the 4-wk trial may have impacted our results. This time effect was shown in the study of Anugwa et al. (1989), who fed finisher pigs a 40% alfalfa diet and found no statistically significant effects on visceral organ weights (heart, liver, spleen, small intestine, and large intestine) when measured at d 34 of the experiment. However, it was found that liver weight (relative to body weight) was higher in alfalfa-fed pigs compared with the control at d 66 of their experiment.


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  		Table 7. Gastrointestinal (GI) tract characteristics of nursery pigs fed degermed, dehulled corn in Exp. 3a
 
Intestinal morphology data of the ileal segments (villus height, villus width, and crypt depth) in this study were comparable to published values (Jin et al., 1994). We found no differences with regards to villus height or crypt depths between the degermed, dehulled corn diet and the normal corn control, although widths of the ileal villi were greater (P < 0.001) in pig fed degermed, dehulled corn (Figure 1Go). Jin et al. (1994) reported greater villus widths and deeper crypts in the ileum of grower pigs fed a high-fiber diet (16.6% NDF) compared with a low-fiber diet (11.6% NDF), whereas Moore et al. (1988) found no morphological changes in intestinal villus parameters when feeding a basal diet supplemented with high-fiber ingredients to grower pigs. The exact physiological significance of the greater villus widths observed in pigs fed degermed, dehulled corn in this study is not clear.



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  		Figure 1. Ileal villus height, villus width, and crypt depth in grower pigs fed degermed, dehulled corn or corn grain in Exp. 3. aValues represent least square means for 12 pigs per treatment. Pigs were housed four per pen in a nursery barn and consumed feed and water on an ad libitum basis. bExperimental nursery diets contained either degermed, dehulled corn (56%) or corn grain (58%) as the major dietary grain source and were fed to pigs for 28 d. On d 28, pigs were humanely killed and a 3-cm cross section of the ileum was obtained and prepared for histology slides. cFour well-oriented ileal villi and associated villus height, villus width, and crypt depth were evaluated per tissue. ***Means differ within an ileal tissue parameter at P < 0.001.

 
Environmental Implications of Degermed, Dehulled Corn
Although these studies were designed specifically to assess the nutritional value of degermed, dehulled corn as a feed ingredient in swine diets, the potential of these feed ingredients to reduce nutrient excretion can be speculated. From this study, we observed that the removal of the hull and germ components of the corn kernel results in a low-fiber feed ingredient. This reduction in fiber content had a beneficial effect on digestibility (Table 4Go), fecal excretion, and N excretion (Table 8Go). In Exp. 1, feeding degermed, dehulled corn to pigs resulted in a 67% reduction in fecal excretion compared with feeding corn grain (P < 0.001). Also, a 29% reduction in N excretion (as % of N intake) was observed in pigs fed degermed, dehulled corn compared with corn grain (P < 0.001). However, the excretory route of N was different in pigs fed corn grain compared with degermed, dehulled corn with significantly more urinary N excreted in pigs fed degermed, dehulled corn. This finding is in line with our expectations that dietary fiber content has a major impact on the N excretion pattern in swine. Fiber increases the flow of fermentative energy substrate and N (of both exogenous and endogenous origin) into the large intestines. Under fermentation conditions (as with higher dietary fiber intake), ammonia, partially derived from urea from the bloodstream, is rapidly utilized by the microflora for the "de novo" synthesis of bacterial protein and is excreted in the feces. Due to the fact that incorporation of ammonia into bacterial protein results in an overall decrease in ammonia available for absorption into the blood and subsequent assembly into urea in the liver, a shift in the excretory pattern of N takes place with more N excreted in the feces with a concomitant decrease in urinary N excretion (Low, 1985). As suggested by the ileal digestibility data in Exp. 2, feeding pigs degermed, dehulled corn resulted in less fermentable substrate presented to the large intestine thus allowing more N absorption and subsequent N excretion in the urine. The excretory route of N has a major impact on ammonia emissions (Canh et al., 1997). Ammonium N that is assimilated into an organic form via bacterial protein production in the large intestine and excreted in the feces is less rapidly degraded to volatile ammonia as compared with urinary N in the form of urea which is rapidly volatilized to ammonia. Also, the reduced fermentative properties of degermed, dehulled corn will most likely lead to lower VFA production in the large intestine, thus resulting in a higher colonic and(or) manure pH which has been shown to augment ammonia emissions (Canh et al., 1998; Mroz et al., 2000). For this matter, the increased urinary N excretion observed in degermed, dehulled corn and its potential impact on ammonia emission warrant further research.


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  		Table 8. The impact of degermed, dehulled corn on fecal excretion and N excretory patterns in grower pigs in Exp. 1a
 
Feeding degermed, dehulled corn to pigs may also have a beneficial effect on odor production. Data on ileal digestibility (Table 5Go) suggest that pigs fed degermed, dehulled corn will have 45% less DM material entering into the cecum and large intestine of the pig. Given that the production of malodorous compounds in swine feces is predominantly a result of the fermentation of undigested feed residues in the large intestine (Mackie et al., 1998), these data suggest that feeding degermed, dehulled corn to pigs has the potential to reduce odor emissions.

Although this discussion is based on data from pigs fed either degermed, dehulled corn or the corn grain as the sole energy and protein ingredient, recent data from our lab suggest that these effects will be additive when degermed, dehulled corn is incorporated into a balanced swine diet (Moeser and van Kempen, 2002). Assuming that there will be no associative effects of a complete replacement of corn grain with degermed, dehulled corn in a typical corn-soybean meal based diet (containing 74% corn and 23% soybean meal), our excretion data indicate that this will result in a reduction in fecal excretion by approximately 52%.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
Literature Cited
 
Results from this study suggest that processing corn to remove poorly digestible fiber fractions significantly improves the digestibility and retention of energy and nitrogen. In addition, reductions in dietary fiber content via addition of degermed, dehulled corn to pig nursery diets improve feed efficiency by 4%. The use of degermed, dehulled corn in pig diets has potential to greatly reduce fecal and nitrogen excretion, thus providing a potential means to reduce the negative environmental impacts of intensive pig production. Future research should focus on the effects of degermed, dehulled corn on nutrient excretion when incorporated into a complete feed and the long-term health effects of feeding this product to pigs, specifically the potential occurrences of gastric ulcers.

Received for publication December 12, 2001. Accepted for publication June 12, 2002.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results and Discussion
 Implications
 Literature Cited
 


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