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Intestinal morphology and enzymatic activity in newly weaned pigs fed contrasting fiber concentrations and fiber properties¹

M. S. Hedemann^*,2, M. Eskildsen^*, H. N. Lærke^*, C. Pedersen^,3, J. E. Lindberg, P. Laurinen and K. E. Bach Knudsen^*

^* Department of Animal Health, Welfare and Nutrition, Danish Institute of Agricultural Sciences, Research Centre Foulum, 8830 Tjele, Denmark; and Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management, SE-750 07 Uppsala, Sweden; and MTT Agrifood Research Finland, Animal Production Research, FIN-05840 Finland

	Abstract

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The main objective of this study was to determine the effect of fiber source and concentration on morphological characteristics, mucin staining pattern, and mucosal enzyme activities in the gastrointestinal tract of pigs. The experiment included 50 pigs from 10 litters weaned at 4 wk of age (BW 8.6 ± 1.4 kg) and divided into 5 treatment groups. Diets containing fiber of various physico-chemical properties and concentrations were formulated to contain 73, 104, or 145 g of dietary fiber/kg of DM. The diets were based on raw wheat and barley flours. Pectin and barley hulls, representing soluble and insoluble fiber sources, respectively, were used to increase the fiber concentration. The pigs were fed the experimental diets for 9 d, and then the pigs were euthanized and the entire gastrointestinal tract was removed. Tissue samples were taken from the mid and distal small intestine and from the mid colon. Inclusion of pectin in the diets significantly decreased (P < 0.001) ADFI and ADG compared with pigs fed no pectin. The villi and the crypts were shorter in pigs fed pectin-containing diets, but the villous height/crypt depth ratio was unaltered. Pectin significantly decreased the area of mucins in the crypts of the small intestine, indicating that the pigs fed the pectin-containing diet would probably be more susceptible to pathogenic bacteria, although this cannot be separated from the impact on ADFI. The lectin-binding pattern of the intestinal mucosa was unaffected by diet. The activity of lactase and maltase was increased in pigs fed diets with high fiber content, whereas sucrase activity was increased in pigs fed the pectin-containing diets. The activity of the peptidases, aminopeptidase N and dipeptidylpeptidase IV, was increased when feeding high fiber diets, whereas the activity of -glutamyl transpeptidase remained unaffected by the experimental diets. In conclusion, the reduced feed intake observed with the pectin-containing diets could explain the lower villous height and crypt depth observed in this study. However, direct effects of pectin also are possible, and thus further study is warranted. Feeding pigs high insoluble fiber diets improved gut morphology by increasing villi length and increased mucosal enzyme activity when compared with pigs fed pectin-containing diets. The mucin content as determined by staining characteristics suggests that pigs fed high insoluble fiber diets might be better protected against pathogenic bacteria than pigs fed diets high in soluble fiber.

Key Words: digestive enzyme • fiber • gut morphology • mucin • pig

	INTRODUCTION

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After the application of antibiotic growth promoters for weaners ceased as of January 2000 in Denmark, a dramatic increase in postweaning diarrhea has been observed (Callesen, 2004). This has augmented the calls for nutritional strategies that provide protection against postweaning diarrhea.

The weaning process is a unique and difficult period in a pig’s life when the animal is stressed by a change in nutrition, removal from the dam, and a change in physical environment. Associated with the weaning process are changes in gut morphology and reduction in enzyme activity of the small intestine, which causes decreased digestive and absorption capacity (Pluske, 2001). Studies in older pigs have shown that the various types of plant carbohydrates behave differently in the gastrointestinal tract of pigs. Inclusion of soluble non-starch polysaccharides (NSP) in the diet can stimulate the growth of a commensal gut flora, leading to increased production of short-chain fatty acids, and a lower pH in the large intestine (Bach Knudsen et al., 1991). Short chain fatty acids can inhibit the growth of many pathogens, the majority of which prefer neutral or slightly alkaline environment for growth (Gibson and Wang, 1994), and low pH has been shown to have negative effect on the growth of bacterial pathogens like Escherichia coli and Clostriduim perfringens (Wang and Gibson, 1993). However, soluble NSP, in particular when provided as purified sources, increases luminal viscosity leading to slower absorption with a risk of reduced ileal digestibility (Johansen et al., 1997). Insoluble NSP reduce the transit time and provide substrate that is slowly degradable by the microflora in the distal large intestine (Freire et al., 2000).

The study’s objectives are to investigate the interactions between dietary fiber (DF) concentration and components with varying physiochemical characteristics on gut morphology and enzymatic activity in the intestinal mucosa during the postweaning period.

	MATERIALS AND METHODS

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The experiment was approved by the ethical committee of the Uppsala Region, Sweden.

Animals and Housing
The study, carried out at the Swedish University of Agricultural Sciences, utilized 50 castrated males (Yorkshire x Landrace), 5 pigs/litter from 10 litters. The pigs had access to a commercial cereal-based diet from 21 d of age and were weaned at 27 ± 4 d of age (BW 8.6 ± 1.4 kg) and assigned to a dietary treatment based on BW and litter. The experiment was carried out in 5 replicates of 2 pigs per dietary treatment housed together in a pen. The pigs were weighed at the beginning and end of the experiment (9 d).

Diets and Feeding
Five experimental diets were formulated to contain carbohydrates with different physicochemical properties at different concentrations (Table 1). The carbohydrates of the basal low fiber diet (LF) were from raw wheat and barley flours. Two diets with a medium DF concentration (104 g of DM/kg) were made by including either pectin (Genu pectin type B Rapid Set, CP Kelco, Lille Skensved, Denmark) with approximately 75% degree of methylation at 71 g·kg^–1 as-fed (MFP) or barley hulls at 96 g·kg^–1 as-fed (MFH) to the basal diet. Two high fiber diets (145 g of DF/kg of DM) were formulated by adding barley hulls at 191 g·kg^–1 as-fed (HFH) or pectin and barley hulls at 71 and 96 g·kg^–1 as-fed, respectively (HFP), to the basal diet (Table 1). The pectin source used in the MFP and HFP diets contained approximately 50% sucrose. To avoid differences in the sucrose content of the diets, 2.1% sucrose was added to the LF, MFH, and HFH diets. With the purpose of balancing the reduced amount of protein from whey protein concentrate and cereals, lysine, threonine, and methionine were added to the diets to meet or exceed the requirements for AA (NCPP, 2005). The pigs were fed ad libitum, and water was supplied with a low-pressure water nipple. Daily feed consumption was recorded.

Samples for Microscopy
After 24 h in the neutral buffered formalin, the tissue samples were carefully cleaned of remaining digesta using deionized water and then transferred to a fresh solution of 4% neutral buffered formalin. Subsequently, the samples were dehydrated, infiltrated with paraffin wax, and stored. Six slides were prepared from each sample, and each slide contained a minimum of 4 sections cut at 4-µm thickness, at least 50 µm apart.

The sections were deparaffinized and hydrated, and then were processed for carbohydrate histochemistry using either the periodic acid-Schiff (PAS) reaction or the alcian blue reaction at either pH 2.5 or pH 1.0 according to Kiernan (1990). For the PAS reaction, the sections were placed in 1% periodic acid (Merck 524) for 10 min. The sections were rinsed in water and placed in Schiff’s reagent (Merck 1.09033) for 20 min. After a rinse in water, the sections were counterstained with Mayer’s hematoxylin, dehydrated, and covered with a cover slip. For the alcian blue reactions, the sections were placed in 1% alcian blue (Sigma A3157) in either 3% acetic acid (Merck 63), pH 2.5, or in 0.1 M HCl, pH 1.0, for 30 min. The sections were rinsed in 0.1 M HCl or 3% acetic acid (the solvent for the dye) and subsequently washed in water. The sections were counterstained with eosin, dehydrated, and covered with a cover slip. The PAS reaction stains for neutral mucins, the alcian blue reaction at pH 2.5 stains for carboxylated or sulfated types of acidic mucins, and the alcian blue reaction at pH 1.0 stains for sulfomucins (Kiernan, 1990).

Carbohydrate histochemistry was evaluated as described previously (Brunsgaard, 1997). Briefly, 15 well-oriented villi and crypts were selected on each slide. For each villous and crypt, the area of mucin granules with a clear positive reaction for neutral mucins, acidic mucins, or sulfomucins was determined using a computer-integrated microscope and an image analysis system (Quantimet 500MC, Leica, Cambridge, UK). This area included the mucous material present in the crypt lumen. Because the histochemical procedure used in our study stains the granules of all mucous cells (goblet cells and crypt secretory cells) as well as the apical secretion of these cells, these are all included in the measurements.

The slides stained for neutral mucins were further used to determine the area, height, and density of the crypts and villi. Moreover, thickness of the muscularis externa was measured. The area of crypts or villi was determined as the area encircled by the basement membrane and the crypt mouth, the basement membrane and the end of the villi, respectively, on 15 well-determined crypts or villi. The crypt depth was determined as the distance between the basement membrane and the crypt mouth, and the villous height was determined as the distance between the crypt mouth and the end of the villi. The density of crypts and villi was determined as the number of crypts or villi present over a defined distance across the luminal part of the mucosa.

Mitotic Counts
After 24 h in Clarke’s fixative, the tissue samples for mitotic counts were transferred to 70% ethanol and stored at +5°C. The mitotic counts in the crypts were performed as described by Goodlad (1994). The counts were performed with a small piece (2 x 2 mm) of tissue hydrated through a graded series of alcohols to 25% ethanol. The samples were hydrolyzed for 14 min in 1 M HCl at 60°C, then placed in Schiff’s reagent (Goodlad, 1994). The crypts were displayed by microdissection under a stereomicroscope (Leica MZ6, Leica Microsystems AG, Wetzlar, Germany), and the number of native mitoses in 20 crypts was counted using a 40x objective on the light microscope.

Lectin Histochemistry
Lectin histochemistry was performed as described previously by Hedemann et al. (2005) using the following biotin labeled lectins: Galanthus nivalis lectin (GNA) is specific for -D-mannose; Maackia amurensis lectin is specific for -2,3 neuraminic acid; and Sambucus nigra lectin for -2,6 neuraminic acid. The lectins were supplied by EY Laboratories Inc., San Mateo, CA.

The slides processed for lectin histochemistry were evaluated for staining frequency and intensity of the goblet cells/mucous cells, and the cytoplasm and the apical membrane of the epithelial cells. The evaluation was done separately on the epithelial cells in the villi and the crypts. The values used for scoring the frequency of cells with positive lectin reactivity were (1): no cells; (2) between 0 and 25% of cells; (3) between 25 and 75% of cells; and (4) more than 75% of cells. The values used for scoring intensity of lectin reactivity were (1) none, (2) weak, (3) moderate, and (4) heavy staining. The scorings were done using a 25x objective on the light microscope by one individual who was blinded to the treatments. The lectin score was calculated as the product of staining intensity and proportion of stained cells of each segment in each pig. The lectin scores were thus: 1 = no reactivity; 2 to 4 = low reactivity; 5 to 9 = moderate reactivity; >10 = high reactivity.

Enzyme Activity
After thawing, the mucosa of the intestinal segment was scraped from the underlying muscular layers. The mucosa was homogenized in aqueous Triton X-100 (6 mL/g of mucosa) using an Ultra Turrax T 25 (Janke & Kunkel GMBH & Co. KG, Staufen, Germany) equipped with a S25N-8G probe. A sample of the homogenate was taken for the determination of alkaline phosphatase (AP) before the centrifugation. After centrifugation (20,000 x g, 60 min) the sediment was dissolved in a similar volume of aqueous Triton X-100, and centrifugation was repeated. The activity of aminopeptidase N (APN) was determined in both supernatants, whereas the remaining enzymes were determined only in the supernatant from the first centrifugation due to very low activity in the second supernatant (M. S. Hede-mann, unpublished data).

The procedure for determining the concentration of protein in the homogenate (Lowry et al., 1951) was modified and performed in a 96-microwell plate using BSA (A 7638, Sigma Chemical, St. Louis) as the standard. The activity of APN, -glutamyl transpeptidase and dipeptidylpeptidase IV was measured using L-ala-nine-4-nitroanilide (101014, Merck, Darmstadt, Germany), -L-glutamic acid 3-carboxy-4-nitroanilide (G 5008, Sigma), and glycyl-L-proline-4-nitroanilide (L1880, Bachem Feinchemikalien AG, Bubendorf, Switzerland), respectively, as substrates (Hedemann et al., 2003).

Lactase, maltase, and sucrase activities were determined according to Dahlqvist (1968) using a glucose kit (166 391, Boehringer Mannheim, Mannheim, Germany) to determine the amount of liberated glucose. The activity of AP was measured using the AP reagent (245-20 ALP, Sigma).

The enzyme activities were expressed as units per milligram of protein, except for AP that was expressed as units per gram of mucosa. One unit was defined as the amount of enzyme that hydrolyzed 1 µmol of the substrate per min.

Chemical Analyses
All feed samples were milled through a 0.5-mm mesh screen (Cyclotec 1093 Sample mill, Foss Tecator, Hoeganaes, Sweden) before analysis. The DM was determined by freeze drying followed by drying at 105°C for 20 h, and ash was determined by combustion at 525°C for 6 h (AOAC, 1990). Crude protein (N x 6.25) was determined by the Kjeldahl method (AOAC, 1990) using a Kjell-Foss 16200 autoanalyser (Foss, Hillerød, Denmark). Total lipids (HCl fat) were extracted with diethyl ether, after acid hydrolysis (Stoldt, 1952). Sugars (glucose, fructose, and sucrose) and fructans were determined by an enzymatic-colorimetric assay (Larsson and Bengtsson, 1983) and starch by the enzymatic-colorimetric method as described by Bach Knudsen (1997). Neutral NSP and constituent sugars were analyzed as alditol acetates by gas chromatography and uronic acids by colorimetry described in detail by Bach Knudsen (1997). Klason lignin was measured gravimetrically as the residue resistant to 12 M H₂SO₄ (Theander and Åman, 1979). Content of DF was calculated as

Statistical Analyses
Performance data were analyzed using the GLM procedures of SAS (SAS Inst. Inc., Cary, NC). The pen was used as the experimental unit. The main effect of diet, with beginning weight of the pigs as covariate, was assessed. In addition, a supplementary model was applied to selectively separate the effects of fiber concentration and type of fiber. For this model, only diets MFH, MFP, HFH, and HFP were included.

The morphological and histological responses and the enzyme activities of the small intestine were analyzed as repeated measurements using the mixed procedure of SAS (Littell et al., 1996), with diet as the between-animal effect and segment as the within-animal effect according to the following model:

[1]

where _i is the effect of diet (i =LF, MFH, MFP, HFH, or HFP), U_j is the litter (j = 1,...,10), (U)_ij refers to the individual pig, _k is the segment (SI50, SI90), _ik is the interaction between diet and segment, and the term _ijk ~ N(0, ²) represents the random error.

In addition to model 1, a supplementary model was applied to selectively separate the effect of fiber concentration and type of fiber. For this model only diets MFH, MFP, HFH, and HFP were included. The supplementary model was:

[2]

where _i is the content of pectin (i = yes, no); ß_j is the fiber concentration (j = medium, high); (ß)_ij is the interaction between pectin and fiber concentration; U_k is the litter (k = 1,...,10); _l is the segment; ß_il is the interaction between pectin and segment; ß_ijl is the interaction between fiber concentration and segment; ß_ijl is the interaction between pectin, fiber concentration and segment; and _ijkl ~ N(0, ²) represents the random error. The morphological and histological responses of the colon were analyzed according to model (1) and (2), but omitting the effect of segment and the interactions between segment, pectin, and fiber concentration.

Results are expressed as least squares means and SEM. For 3 responses, the area of neutral and acidic mucins in the crypts in the colon and the activity of AP, the data were analyzed on a logarithmic scale to obtain normality. The response estimates were subsequently transformed back to the original scale. Because confidence intervals on the original scale are not symmetric around the response estimates, the confidence limits rather than the SE are presented for those responses. Treatment differences are considered significant at = 0.05.

	RESULTS

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Diets and Animal Performance
As expected, there were differences in chemical composition of the diets relative to starch, polysaccharides of NSP, and Klason lignin (Table 1). With increasing DF concentrations, NSP increased whereas starch decreased. The pectin diets contained the most soluble noncellulose polysaccharides and greatest amount of cellulose was in the LF diet and the diets containing barley hulls. The amount of sugars, where sucrose makes up the major part (results not shown), did not differ between the diets.

The diets affected ADG, ADFI, and G:F of the pigs (Table 2). Pigs fed diets containing pectin had lower ADG (P < 0.003), ADFI (P < 0.003), and G:F (P < 0.009) than pigs fed the LF, MFH, or the HFH diets.

The crypt depth differed (P < 0.001) significantly between the locations in the small intestine, whereas the number of crypts per millimeter did not differ between SI50 and SI90.

The villous height/crypt depth ratio differed by location (P = 0.04) and ranged from 0.96 to 1.19 at SI50 and from 1.06 to 1.24 at SI90 but was unaffected by dietary treatment.

The epithelial cell proliferation as determined by the number of native mitoses was affected by the fiber content of the diets in the small intestine. Pigs fed HFH and HFP had a lower number of native mitoses than pigs fed LF, MFP, and MFH. Pectin tended to lower the mitotic counts in the small intestine (P < 0.09), whereas the mitotic counts in the colon were unaffected by the experimental diets. The mitotic counts correlated to the crypt depth in SI50 (r = 0.36, P = 0.01), but there was not a correlation in the SI90 or Co50 sections (results not shown).

The experimental diets did not affect the thickness of the muscularis externa in the small intestine or the colon (results not shown). The thickness was significantly affected (P < 0.001) by the position in the small intestine with SI50 having 176 ± 6 µm and SI90 having 254 ± 13 µm. In the colon the average muscle thickness was 188 ± 7 µm.

Mucin Staining Characteristics and Lectin Histochemistry
In general, the staining area of sulfo, acidic, or neutral mucin on villi was not affected by diet, but there was a tendency (P = 0.07) toward a decrease in the area of neutral mucins on villi in pigs fed pectin diets (Table 4). Pectin significantly decreased the area of the mucins in the crypts in the small intestine. Diet had no influence on the mucinstaining pattern in the colon.

No effect of fiber concentration or interaction between fiber concentration and pectin was observed on mucin staining characteristics at either crypt or villi.

Diet did not affect the mucin staining area of the total villi or crypt area except for the area of sulfomucins on villi (results not shown). The mucin staining area on the villi accounted for approximately 2% of the total villous area (Table 5). The neutral mucins covered 6.7 and 7.9% of the crypt area in the SI50 and SI90 (P < 0.05), respectively. For sulfomucins and acidic mucins, the mucin staining area of the total crypt area differed significantly between the SI50 and SI90 being 75% greater in the SI90 (P < 0.05). In the colon, neutral mucins covered 19.4% of the crypt area and sulfomucins and acidic mucins covered 9.7 and 14.5%, respectively.

View this table: [in this window] [in a new window]   Table 7. Activity of lactase, maltase, sucrase, aminopeptidase N, dipeptidylpeptidase IV, -glutamyl transpeptidase, and alkaline phosphatase at 50 and 90% of the small intestinal length of pigs fed different fiber concentrations and sources postweaning1

	DISCUSSION

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It is widely established that postweaning feed intake is an important factor in the digestive development of pigs (Pluske et al., 1996; van Beers-Schreurs et al., 1998; Marion et al., 2002). In the current study, feed intake depended on fiber composition with pectin-containing diets having a lower feed intake. The inclusion of pectin in the diets resulted in increased luminal viscosity and water binding capacity (J. E. Lindberg, unpublished data), which may have slowed down digesta passage and increased the satiety of the pigs, leading to lower feed intakes. Additionally, the citrus pectin included in the diets may have had a negative impact on taste, mouth feel of the diets, or both.

A period of low feed intake is likely to result in damaged gut architecture (Pluske et al., 1997), and several authors have found that the effect of diet composition on mucosal integrity in the small intestine has been shown to be overridden by diminished feed intake (van Beers-Schreurs et al., 1998; Spreeuwenberg et al., 2001; Vente-Spreeuwenberg et al., 2003). Marion et al. (2002) showed that 56% of the variation in the villous height in the proximal small intestine was explained by the level of feed intake. The association between feed intake and villous height has been suggested to determine postweaning weight gain (Pluske et al., 1996), which is supported by the current study.

The pectin-fed pigs that had the lowest feed intake in the present experiment also had the shortest villi. Apart from the effect on feed intake, pectin per se may also have influenced the intestinal architecture. Feeding a diet containing carboxymethylcellulose, which increased the intestinal viscosity, reduced the villous height and increased the crypt depth (McDonald et al., 2001). However, feeding a low viscosity carboxymethylcellulose resulted in longer villi (McDonald et al., 2001). Conflicting results on the effect of soluble fiber on the intestinal morphology also exists in growing pigs, rats, and chickens (Glitsø et al., 1998; Iji et al., 2001; Kim, 2002). Feeding pectin-containing diets resulted in the shortest crypts; this is in contrast to the literature where it has been shown that the consequence of low feed intake or intake of viscous diets is crypt elongation (Pluske et al., 1996; McDonald et al., 2001). The crypt depth was correlated to the mitotic counts in SI50 in the current study, and because the crypt depth is an indication of the cell production in the crypts (Hedemann et al., 2003) this indicates that the low feed intake of the pectin-fed piglets reduced the production of new cells in the intestine.

In the current study, the fiber concentration had no influence on the morphological characteristics, and the mitotic counts in the small intestine were lower in pigs fed high fiber diets. In contrast, the inclusion of 10% wheat straw to a low fiber diet resulted in deeper crypts in the jejunum and ileum and augmented cell division in growing pigs (Jin et al., 1994). The discrepancies in the present experiment may be because the pigs were newly weaned, and the microflora was not adapted to the dietary fiber (Jensen, 1998).

Free AA were added to the medium and high fiber diets to balance the reduced amount of whey protein concentrate in these diets. The calculated content of AA in the diets all exceed the recommendations given by NCPP (NCPP, 2005). In a recent study it was shown that feeding low-protein, AA-supplemented diets did not result in any morphological changes (Nyachoti et al., 2006). Hence the morphological differences observed in the present investigation cannot be attributed to the use of crystalline AA in some of the diets.

The villous height/crypt depth ratio is a useful criterion for estimating the digestive capacity in the small intestine (Montagne et al., 2003). In this study, the maintenance of the villous height/crypt depth ratio suggests that a reduction in villous height is less deleterious when it is not accompanied by increased crypt depth. Furthermore, the number of villi and crypts per millimeter of intestine was increased in pectin-fed pigs, which increased the absorptive surface. In rats, pectin-containing diets have been shown to either increase (Tasman-Jones et al., 1982) or decrease (Brunsgaard and Eggum, 1995) the villi density.

Villous atrophy is generally assumed to be associated with reduced mucosal enzyme activity. As the cells lost are the mature enterocytes where the digestive enzymes are located, and decreased mucosal enzyme activity has generally been observed in association with weaning (Hampson and Kidder, 1986; Hedemann et al., 2003). In rats and pigs, it has been shown that soluble fiber sources increase the brush border enzyme activity (Chun et al., 1989; Lizardo et al., 1997). However, in this study, the greatest enzyme activities were observed in the pigs with the shortest villi that were fed the HFP diet. It has been observed that pectin increases the plasma glucagon-like peptide-2 concentration (Fukunaga et al., 2003), an intestinotrophic hormone that reduces mucosal atrophy by decreasing apoptosis and proteolyses (Burrin et al., 2000). This led the authors to hypothesize that the negative effect of the low feed intake in the pectin-fed pigs is counteracted by a lower level of apoptosis in the intestine of these pigs. This aspect, however, warrants further investigations. In the current study, pectin (or feed intake) exerted main effects on the intestinal morphology, whereas the fiber concentration mainly affected the enzyme activities. Hence in agreement with other studies, it may be concluded that the effects of dietary fiber on epithelial structure are not clearly associated with changes in enzymatic activities (Montagne et al., 2003).

The number of goblet cells in the small intestine has been shown to increase after weaning, whereas no changes were observed in the hindgut (Brown et al., 1988), and dietary fiber modifies the nature of the mucins secreted (More et al., 1987). The lower mucin staining area in the small intestinal crypts of the pectin-fed pigs implies a lower production and secretion of mucin. This effect was primarily seen for the acidic and sulfated subtypes, which indicates immaturity of the mucins secreted (Koninkx et al., 1988). Because acidic mucins, particularly sulfomucins, protect against bacterial translocation (Deplancke and Gaskins, 2001), the pectin-fed pigs may be more susceptible to infections.

The mucin staining area in both the small intestine and the colon was considerably lower than that observed in slaughter pigs (Brunsgaard, 1998; Hedemann et al., 2005) implying a decreased susceptibility to certain intestinal infections as the pig proceeds from the weaning through the fattening period (Brunsgaard, 1997).

Lectins are carbohydrate-binding proteins that can be used to characterize glucoconjugates covering the epithelium, which are essential to provide a barrier to invading pathogens (Neutra and Forstner, 1987). Age influences the lectin-binding characteristics (Jaeger et al., 1989), and differences in lectin binding can potentially serve as a marker for maturational status of the intestine. Mucosal lectin binding is affected by dietary changes, but none of the observed differences were specific to a particular diet. This may be due to the age of the pig and its gut maturity.

In conclusion, the morphological changes observed in the current study could be explained by the reduced feed intake in the pigs fed pectin-containing diets or as a direct effect of pectin. In contrast the mucosal enzyme activity was mainly affected by the fiber concentration. The mucin staining characteristics suggest that pigs fed pectin-containing diets may be more susceptible to pathogenic bacteria. Overall the results of the present investigation showed that pigs fed HFH had the best morphological and enzymatic characteristics 9 d post-weaning.

	IMPLICATIONS

Top Abstract INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION IMPLICATIONS LITERATURE CITED

 
Different types and amounts of fiber seem to be useful in optimizing the function of the gut of a newly weaned pig. Of particular importance may be the improvement in gut morphology and enzymatic activity when an insoluble fiber source is utilized, whereas the possible negative impact of soluble fiber sources on the feed intake should be considered. Additional investigations are necessary to determine if fiber may be useful in newly weaned pigs in lieu of antibiotics.

	Footnotes

 
¹ Financial support provided by the Nordic Joint Committee for Agricultural Research is gratefully acknowledged.

³ Present address: South Dakota State University, Animal and Range Science, Brookings 57007.

² Corresponding author: mette.hedemann{at}agrsci.dk

Received for publication June 21, 2005. Accepted for publication January 16, 2006.

	LITERATURE CITED

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