Effect of dietary ®bre source on total tract
digestibility, caecum volatile fatty acids and
digestive transit time in the weaned piglet
J.P.B. Freire
a,*, A.J.G. Guerreiro
a, L.F. Cunha
a, A. Aumaitre
b aDpto. de Producao Agricola e Animal, Seccao de Producao Animal, Instituto Superior de Agronomia,Tapada da Ajuda, 1349-017 Lisbon, Portugal
bUnite Mixte de Recherches sur le Veau et le Porc, 35590 St. Gilles, France
Received 20 October 1999; received in revised form 25 April 2000; accepted 5 July 2000
Abstract
Effects of the use of 200 g of either wheat bran, sugar beet pulp, soya bean hulls or alfalfa meal per kilogram diet on the digestive process of the weaned piglet were studied on 24 DurocLandrace male piglets, weaned at 28 days of age. Piglets had an initial mean live weight of 7.92(1.1) kg and were randomly distributed in six successive blocks of four animals. The total tract apparent digestibility (TTAD) was 0.872, 0.887, 0.815 and 0.824 for energy and 0.847, 0.833, 0.665 and 0.795 for nitrogen for the wheat bran, sugar beet pulp, soya bean hulls and alfalfa meal diet, respectively P<0:01. The TTAD values for NDF were 0.615, 0.861, 0.721 and 0.593, and for ADF were 0.390, 0.779, 0.708 and 0.457 in diets based on wheat bran, sugar beet pulp, soya bean hulls and alfalfa meal, respectively P<0:01. The level of volatile fatty acids (VFAs) in the caecum contents changed from 3.80 to 4.96 mg gÿ1when sugar beet pulp replaced soya bean hulls, respectively, the later producing a higher proportion of acetic acid P<0:05. The average molar proportions were 0.635, 0.245 and 0.10 for acetic, propionic and butyric acid, respectively. Soya bean hulls in the diet increased the level of total VFA by 15 or 30% when compared with the wheat bran or with the sugar beet pulp and the alfalfa meal, respectively
P<0:05. For a constant nitrogen intake, the diet containing soya bean hulls supported the lowest nitrogen retention. The mean retention time was 51.5, 49.9, 56.9 and 37.7 h for diets based on wheat bran, sugar beet pulp, soya bean hulls and alfalfa meal, respectively P<0:01. In contrast to alfalfa meal, the soya bean hulls reduced the chromium excretion rate by 40% and delayed the in¯exion point of the excretion curve by 11 h, and consequently the digestive transit time. In conclusion, sugar beet pulp has the highest degradation rate of NDF and ADF fractions. The inclusion of soya bean hulls leads to a decrease in the energy and nitrogen digestibility of the
87 (2000) 71±83
*Corresponding author. Tel.:351-21-3653408; fax:351-21-3630734
E-mail address: jpfreire@isa.utl.pt (J.P.B. Freire).
weaning diet. Finally, alfalfa meal was the most effective ®bre source to regulate the digestive transit time.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Piglets; Dietary ®bre; Digestibility; Volatile fatty acids; Transit time
1. Introduction
The bene®cial effect of using non-starch polysaccharides (NSPs) in the diet of the weaning piglet is based on the improvement of their health status (Aumaitre, 1969). In fact, dietary ®bre can stimulate the digestive compartments (Longland et al., 1994) and regulate the digestive transit time by an increase of the faecal volume (Knudsen and Hansen, 1991).
Nevertheless, in the growing pig, the digestibility of energy is negatively affected by the neutral detergent ®bre content of the diet (Noblet et al., 1993). In the piglet, the use of NSP from wheat and barley in the weaning diet is generally associated with a reduction of the total tract apparent digestibility (TTAD) of dry matter (DM) and energy (Bengala Freire et al., 1990; Freire et al., 1998).
However, this depressive effect of dietary ®bre source on TTAD depends on its composition due to different degradation rates in the hindgut (Chabeauti et al., 1994) and to differences in the digestive transit time (Aman and Graham, 1991; Chesson, 1991). In fact, the ability of 4-week old piglets to digest particular ®bre sources such as sugar beet pulp without the depressive effects on TTAD of other dietary components has been clearly demonstrated (Lizardo et al., 1997).
In the growing pig, digestive contents remain in the large intestine for more than 40 h, mostly depending on the bulk capacity of the dietary ®bre (Knudsen and Hansen, 1991). In the case of soluble and easy to ferment ®bre, the increase of faecal volume is small. In contrast, ®bre sources with more ligni®ed cell walls have low water holding capacity but are more resistant to the micro¯ora activity, and more effective in increasing the faecal volume and reducing the digestive transit time (Chesson, 1991). Moreover, in contrast to the digestive transit time measurements performed with growing pigs (Pond et al., 1986) or peccary species (Comizzoli et al., 1997), the mean retention time (MRT) of the undigested material in the digestive tract has never been determined in 4-week old piglets.
Acetic, propionic and butyric acids are the major end products of ®bre degradation in the hindgut of pigs (Ratcliffe, 1991). Therefore, the level of the volatile fatty acids (VFAs) in the caecum contents can provide good prediction of the degree of fermentation of the dietary ®bre. In the growing pig, this level ranges between 80 and 140 mmol lÿ1, varying with the contents and composition of the dietary ®bre (Sauer et al., 1991; Knudsen et al., 1993). The VFAs are known as an energy source for pigs (Dierick et al., 1989), in particular butyric acid can be used by the intestinal epithelium as an energy source (Argenzio and Southworth, 1974) and can support the development of the digestive intestinal enzymes (Lizardo et al., 1997).
caecum VFAs concentration and the digestive transit time of the weaned piglet in order to explain differences in the TTAD values of the diets.
2. Materials and methods
2.1. Animals and diets
The effect of NSPs on the digestive process of the weaned piglet was studied using 24 DurocLandrace male piglets, weaned at 28 days of age and with an initial average live weight of 7:921:1 kg. The piglets, housed individually in metabolism cages, were from six sows (four pigs per sow) and those within each litter were allotted, according to their liveweight, to four groups. Each group received, on a pair feeding basis, one of four experimental diets, presented as 3 mm diameter pellets. The diets contained similar crude protein contents and total amino acids, calcium and phosphorus levels. Wheat bran, sugar beet pulp, soya bean hulls and alfalfa meal commercially available were incorporated at 200 g kgÿ1diet as the major ®bre sources in diets 1, 2, 3 and 4, respectively (Table 1). The chemical composition of the ®bre sources is presented in Table 2.
After a short adaptation period of 4 days, individual measurements were performed during three consecutive periods of 7 days. Faeces and urine were individually collected on the ®rst and third period for determination of TTAD and nitrogen balance. Subsequently, the digestive transit time was controlled during a subsequent period of 5 days. For this purpose, the four sources of ®bre were ®rst marked with 123, 158, 119 and 133 mg of Na2Cr2O7per gram of wheat bran, sugar beet pulp, soya bean hulls and alfalfa meal, respectively, and then incorporated in each experimental diet replacing 50% of the non-marked ®bre, respectively. The marked ®bre sources were prepared according to Uden et al. (1980), the quantity of Na2Cr2O7was adjusted to obtain a concentration of 120 mg Cr gÿ1of NDF. In the ®rst day of this period, the piglets received 300 g of the marked diets in the morning, and 300 g of the non-marked diets in the afternoon. On the following days, each piglet received 600 g of non-marked diets offered in two meals. The faeces were collected every 2 h during the ®rst and second day, every 4 h during the third day and the ®rst half of the fourth day, and every 12 h afterwards. Faeces were weighed and stored atÿ208C for analysis of DM and chromium. At the end of the experiment, the 58-days old piglets were slaughtered under general anaesthesia, after a 16 h-fasting period, the digestive tract was weighed, emptied and the caecal content was collected for analysis.
2.2. Analysis
At the end of each collection period, a representative sample of faeces and urine was individually prepared. Samples of faeces were freeze dried and ground in a hammer mill through a mesh of 1 mm. Similarly, samples of diets were ground to 1 mm before analysis. DM was analysed by oven-drying at 1058C and ash by incineration at 5508C. Gross energy was measured with a peribol calorimeter (Parr 1261, Moline Illinois, USA). The cell wall constituents were analysed for NDF, ADF and ADL determination in a Fibertec apparatus (Tecator 1020, Hogonas, Sweden) according to Van Soest et al. (1991).
Table 1
Composition of the experimental diets (g kgÿ1) and chemical composition (g kgÿ1fresh weight)
Diets
Wheat bran Sugar beet pulp Soya bean hulls Alfalfa meal
Corn starch 408.0 403.2 403.8 404.0
Wheat bran 200.0 ± ± ±
Sugar beet pulp ± 200.0 ± ±
Soya bean hulls ± ± 200.0 ±
Alfalfa meal ± ± ± 200.0
Dry milk 100.0 100.0 100.0 100.0
Fish meal 100.0 100.0 100.0 100.0
Potato protein 100.0 100.0 100.0 100.0
Soya bean oil 50.0 50.0 50.0 50.0
DL-Methionine 1.0 1.5 1.0 1.0
L-Tryptophan ± 0.3 0.2 ±
Calcium carbonate 10.0 ± ± ±
Dicalcium phosphate 16.0 30.0 30.0 30.0
Sodium chloride 5.0 5.0 5.0 5.0
Vitamin trace mineral mixa 10.0 10.0 10.0 10.0
Chemical composition
DM 920.4 926.6 952.4 956.7
Ash 64.2 75.3 68.4 73.6
Crude protein (N6:25) 200.8 202.3 207.8 199.7
NDF 128.0 159.7 130.4 155.9
ADF 34.5 71.3 81.1 87.0
ADL 12.1 6.1 8.0 29.1
Starch 411.2 349.7 337.8 376.9
Gross energy (MJ kgÿ1) 17.87 17.47 17.86 17.72
aMineral and vitamin mixture supplied per kilogram of diet Ð Vit. A: 12,000 IU, Vit. D3: 2000 IU, Vit. E:
20.0 mg, Vit. B1: 1.0 mg, Vit. B2: 4.0 mg, Vit. B6: 1.50 mg, Vit. B12: 0.020 mg, Vit. K3: 2.0 mg, Vit. H2: 0.10 mg, nicotinic acid: 25.0 mg, folic acid: 0.50 mg, panthotenic acid: 15.0 mg, choline chloride: 400.0 mg, calcium iodate: 0.60 mg, manganese (oxide): 40.0 mg, ferrous sulphate (5H2O): 125.0 mg, zinc (oxide):
100.0 mg, copper sulphate (5H2O): 160.0 mg, sodium selenite: 0.150 mg, cobalt sulphate: 0.400 mg,Bacillus
toyoi: 100.0 mg, carbadox: 50.0 mg, ¯avours: 500.0 mg, antioxidant (BHT): 60.0 mg, phosphoric acid: 1050.0 mg, citric acid: 150.0 mg.
Table 2
Chemical composition of the ®bre sources (g kgÿ1fresh weight)
Wheat bran Sugar beet pulp Soya bean hulls Alfalfa meal
DM 886.3 914.7 901.0 898.3
Crude protein (N6:25) 150.9 116.2 147.0 148.2
NDF 406.9 526.5 396.4 442.6
ADF 118.8 224.1 303.0 322.8
Nitrogen of feeds, faeces and urine was analysed by the Kjeldahl method. Starch of feeds was determined enzymatically (Bengala Freire et al., 1990). At slaughter, the caecal content was immediately diluted (in a 10:1 proportion) with an additive prepared with a 1% (w/w) solution of mercuric chloride and 5% (v/v) orthophosphoric acid in distilled water for preservation, according to the methodology of Jouany (1982). Afterwards, the samples were centrifuged at 5000gfor 5 min and the VFAs analysed in the supernatant by gas chromatography in a Perkin Elmer (Model Sigma 3) chromatograph using a Capilar Column Chromopack 7486. Only the three major VFAs were recorded and iso acids were not determined. Chromium in feeds and faeces was analysed by atomic absorption spectrophotometry after digestion of the samples for 2 h at 1408C in 15 ml of concentrated HCl and 5 ml of concentrated nitric acid (Berrow and Stein, 1983).
2.3. Computations and statistic analysis
The TTAD and nitrogen balance results were compared by analysis of variance according to a split-plot design, considering the mean square associated to the interaction litterdiet as the residual error to test the effect of the diet. Data concerning growth performance, weight of the digestive organs and VFA level (expressed by g of cascal content) were compared by an analysis of variance according to a complete block design with the effect of the litters confounded with the effect of blocks.
The cumulative percentage of the marker recovered in faeces was plotted to the time after feeding. These curves expressed a delay in the ®rst appearance of the marker in the faeces and an in¯exion point, so chromium excretion was adjusted according to a non-linear equation (Dagnelie, 1975). The function that better ®tted the excretion of the chromium was the non-linear logistic equation:
YA 1eÿKtÿM
whereYis the cumulative chromium excreted expressed as a percentage of the chromium intake, A the chromium excreted during the time 0 to1 expressed as a percentage of intake,Kthe chromium excretion rate (% hÿ1),tthe time after the intake of the marked feed (h), andM a parameter related with the time of occurrence of the in¯exion point.
The MRT was calculated according to the formula of Faichney (1975): MRTPmiti=
P
mi, where mi is the fraction of the marker excreted at time ti. The digestive transit time was analysed by analysis of variance of the MRT and the parameters (A, K, M) of the logistic equation. When the F value in the analysis of variance was signi®cant, the means were compared by a Duncan's multiple range test (Dagnelie, 1975). All the analysis of variance and the Duncan's test were performed by the SAS program, procedure GLM (SAS, 1991). The computation of the chromium excretion curves was under-taken by the SAS program, procedure NLIN, using the DUD adjustment method (SAS, 1989).
3. Results
The nature of the dietary ®bre signi®cantly changed both growth rate and feed conversion of the weaned piglets. For a constant feed intake, the addition of soya bean
hulls to the diet reduced the daily growth rate by 20% and increased the feed conversion by 17% when compared with the other ®bre sources (Table 3). The sugar beet pulp diet, in comparison with the wheat bran, increased the TTAD of DM and energy (E) by 2.4 and 1.7%, respectively (Table 4). In contrast, the replacement of wheat bran by soya bean hulls or alfalfa meal decreased P<0:01the TTAD values of DM by 4.5 and 4.2% and the TTAD of nitrogen by 21.5 and 6.1%, respectively. Among the four cell wall sources, the sugar beet pulp-based diet showed the highest digestibility for NDF, ADF, hemicellulose (NDF±ADF) and cellulose (ADF±ADL) fractions. Fibre from wheat bran was generally less degraded by the young piglet. In general, TTAD of hemicellulose was high, particularly in the case of the sugar beet pulp-based diet. TTAD of cellulose was also high and similar for sugar beet pulp and soya bean hulls diets but was considerably lower for both wheat bran and alfalfa diets P<0:01. With the exception of the hemicellulose and cellulose fractions, the TTAD was signi®cantly increased between the ®rst and the third experimental period.
The source of ®bre in the weaning diet changed signi®cantly the relative weight of the gut compartments (Table 5). Soya bean hulls increased P<0:05the relative weight of the total and empty small intestine by 15 and 13%, and the weight of the total and empty large intestine by 35 and 16%, respectively P<0:01. The presence of soya bean hulls almost doubled the weight of the large intestine contents when compared with sugar beet pulp.
The concentration of the total VFA levels in the caecum contents at slaughter (Table 6) depended signi®cantly on the source of dietary ®bre. The use of soya bean hulls in the weaning diet increased P<0:05 the concentration of total VFA by 11.2, 30.5 and 27.2% when compared with the wheat bran, the sugar beet pulp and the alfalfa diets, respectively. This effect was associated with an increase in the level of acetic acid, and of the ratio acetate:propionate and acetate:butyrate, which were signi®cantly higher in animals fed with the soya bean hulls diet P<0:01.
For a constant nitrogen intake, soya bean hulls reduced P<0:01the daily nitrogen retention by 25%, when compared with the other ®bre sources (Table 4). Likewise, in
Table 3
Effect of dietary ®bre source on performance of piglets between 32 and 53 days of age
Dietsa Statistical analysisb
Initial weight (kg) 8.03 8.05 7.67 7.92 * NSc 1.15
Final weight (kg) 15.85 15.67 13.88 15.80 NS NS 1.55
Feed intake (kg per day) 0.444 0.434 0.424 0.445 NS NS 0.02 Average daily gain (kg per day) 0.372 a 0.362 a 0.295 b 0.375 a NS ** 0.03
Feed conversion 1.20 a 1.20 a 1.45 b 1.19 a NS ** 0.09
aMeans with the same letters on the same line are not signi®cantly different. bL: litter, D: diet, RSD: residual standard deviation.
animals fed with the diet containing soya bean hulls the amount of retained nitrogen, expressed as a percentage of intake or absorbed, was reduced by 14 and 10 percentage units, respectively.
The analysis of the parameters used to control the digestive transit time (Table 7, Fig. 1) shows a decrease in the transit time with the inclusion of 200 g of alfalfa per kilogram diet. In mean terms, alfalfa almost doubled the chromium excretion rate (K). As a consequence, the excretion time for 25 and 50% of the total chromium intake was reduced by 13 and 22 h, respectively and the MRT was reduced by 15 h P<0:01. In
Table 4
Effect of dietary ®bre source and experimental period on total tract apparent digestibility (TTAD) of dietary components, digestible and metabolizable energy and nitrogen balance
Dietsa Periodsb Statistical analysisc
Wheat
Hemicellulosed 0.698 a 0.927 b 0.742 c 0.764 c 0.678 0.689 ** NSe 0.02
Cellulosed 0.317 a 0.755 b 0.688 b 0.341 a 0.773 0.792 ** NS 0.08
Gross energy 0.872 a 0.887 a 0.815 b 0.824 b 0.837 0.862 ** ** 0.02
DE (MJ kgÿ1)f 16.87 a 16.72 a 15.44 b 15.24 b 15.80 16.31 ** ** 0.42
ME (MJ kgÿ1)g 14.91 a 14.78 a 12.95 b 13.23 b 13.90 14.10 ** NS 0.95
N balance
N intake (g per day) 13.68 13.95 13.79 13.99 10.43 17.46 NS ** 0.36 N retention
(g per day) 10.13 a 10.70 a 7.58 b 9.93 a 6.43 12.92 ** ** 0.95 (% of daily gain) 2.99 a 4.24 b 5.60 c 4.04 b 4.88 3.56 ** ** 0.82 (% of N absorbed) 85.6 ab 90.4 a 78.4 b 88.0 a 80.3 91.3 * ** 8.52 (% of N intake) 72.3 a 75.4 a 52.5 b 70.0 a 61.5 74.1 ** ** 8.54
aFor diet effects, means with the same letters on the same line are not signi®cantly different. bPeriod 1: 32±39 days of age, period 3: 46±53 days of age.
cD: diet, P: period, DP: interaction dietperiod, RSD: residual standard deviation. Interaction DP
was only signi®cant (P<0:01) for N retention expressed in % of daily gain.
dHemicellulose and cellulose are NDF±ADF and ADF±ADL, respectively, according to Van Soest et al.
(1991).
addition, the soya bean hulls reduced the chromium excretion rate by 40% and delayed the in¯exion point of the excretion curve by 11 h.
4. Discussion
4.1. Digestibility
The decrease in the daily growth rate and the increase in feed conversion veri®ed with the incorporation of soya bean hulls in the weaning diet is associated with the decrease of the digestible energy content of the diet (Table 4), which is in agreement with data reported with the growing pig (Quiniou et al., 1999). Furthermore, once the diets were balanced in total essential amino acids, the increase in the urinary nitrogen excretion with the incorporation of soya bean hulls may be the result of a higher microbial production of ammonia in the large intestine, which is then excreted as urinary urea (Ratcliffe, 1991). The increase in DM digestibility with the use of sugar beet pulp may be a consequence of its high level of digestible NDF, ADF, pectins and their constituent monosaccharides and uronic acids (Longland et al., 1994). This result is in accordance with the high fermentation level of this ®bre source, found not only in the growing pig (Graham et al., 1986; Chabeauti et al., 1994) but also in the 6-week old piglet (Lizardo et al., 1997).
Table 5
Effect of dietary ®bre source on the fresh weight of the stomach, the small and large intestine and the intestinal contents (g kgÿ1live weight)
Dietsa Statistical analysisb
Total 10.04 10.73 10.40 10.21 NSc NS 1.44
Empty 7.80 a 9.12 b 8.52 ab 7.79 a NS * 0.76
Stomach content 2.24 1.61 1.88 2.41 NS NS 0.99
Small intestine content 6.11 5.68 7.35 6.00 * NS 2.01
Large intestine content 16.60 a 13.35 a 24.82 b 18.59 a NS ** 4.94
Caecum content 2.63 1.87 2.96 1.20 NS NS 1.05
aMeans with the same letters on the same line are not signi®cantly different. bL: litter, D: diet, RSD: residual standard deviation.
Effect of dietary ®bre source on the concentration of VFAs and pro®le in the caecal contents at slaughter
Hemicellulose (NDF±ADF) (g kgÿ1) 93.5 88.4 49.3 68.9
Cellulose (ADF±ADL) (g kgÿ1) 22.4 65.2 73.1 57.9
aMeans with the same letters on the same line are not signi®cantly different (n6 piglets per diet). bL: litter, D: diet, RSD: residual standard deviation.
cNS: nonsigni®cant.
dVFA concentration (mg gÿ1of caecal content). *P<0:05.
**P<0:01.
Table 7
Effect of dietary ®bre source on the parameters of the mathematical model of chromium excretion
Dietsa Statistical analysisb
aMeans with the same letters on the same line are not signi®cantly different. bD: diet, RSD: residual standard deviation.
cChromium recovered during the period 0 to
1.
dNS: nonsigni®cant. eChromium excretion rate.
fIn¯exion point of the chromium excretion curve. gTime (h) for recovery of 25% of the chromium intake. hTime (h) for recovery of 50% of the chromium intake. iMean retention time.
The lower TTAD of nitrogen (Table 4) for the soya bean hulls diet may be explained by the presence of residual antitrypsin factors (Bengala Freire et al., 1991; Fan et al., 1995) or by an increase in the microbial nitrogen faecal excretion (Stanogias and Pearce, 1985a). In fact, the presence of 50 ga-galactosides per kilogram soya bean hulls can be used as an energy source by the gut micro¯ora with an increase in its fermentative activity (Bengala Freire et al., 1991). Furthermore, the relatively low digestibility of cell walls fractions of the wheat bran or alfalfa diets might be explained by their higher level of lignin (Graham et al., 1986; Kass et al., 1980a). The signi®cant increase in the TTAD of energy and ®brous components with the age of piglets seems to demonstrate a progressive maturation of the digestive tract, which is in agreement with Longland et al. (1994).
4.2. Fermentative activity in the caecum
Considering the mean value for all diets, the levels of acetic, propionic and butyric acid corresponded to 65, 25 and 10% of the total VFA, respectively. These values are in accordance with previous data presented by Kass et al. (1980b) and Sauer et al. (1991). The maximum level of total VFA was observed for soya bean hulls-based diet. This result suggests a high degradation rate in the caecum, and is in agreement with the high digestibility values of the NDF and ADF fractions. The relatively lower values of VFA
measured in the sugar beet pulp diet could also be associated with a higher absorption rate of its metabolites in the caecum. The higher level of butyric acid found in the caecum content of the piglets fed with the wheat bran diet may be generated by small quantities of endosperm that escape digestion in the small intestine and are fermented in the large intestines, lowering the pH in the caecum. The VFA may also stimulate the epithelial mucosa, changing the fresh weight of the small and the large intestine, particularly for the diet based on soya bean hulls (Stanogias and Pearce, 1985b).
4.3. Digestive transit time
The mathematical model describing the chromium excretion ®ts the model reported by Pond et al. (1986) comparing the use of different markers to describe the transit of undigested materials in the growing pig. The alfalfa diet decreased not only the digestive transit time but also the digestibility of the NDF and ADF fractions. These results corroborate the hypothesis of Knudsen and Hansen (1991) that indicated an increase in the transit passage with less degradable ®bres, due to their higher water holding capacity. The delay in the in¯exion point of chromium excretion curve represented a slower digestive transit. According to Knudsen and Hansen (1991), the use of soluble ®bres in the diet such as sugar beet pulp may increase the viscosity of the intralumen contents of the gut, delaying the digestive transit in the small intestine and completing the digestive process in the piglet.
In conclusion, the effect of the sugar beet pulp on the digestible energy of the weaning diet is minimized by the high degradation rate of its NDF and ADF fractions. On the other hand, the soya bean hulls seemed to be less appropriate to the low digestive capacity of the young pig, probably due to the presence of antitrypsin factors and a-galactosides. Finally, among the four ®bre sources studied, the alfalfa meal was the most effective in regulating the digestive transit time. However, its negative effect on the digestible energy of the weaning diet must be considered before recommending its incorporation in the starter diet of piglets.
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