J Sci Food Agric 1997, 74, 244È250

Diurnal Variation in the Composition of IlealDigesta and the Ileal Digestibilities of Nutrients inGrowing PigsHenry Jan Erik and Christel AnderssonJÔrgensen,* Lindberg”

Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Box 7024,S-750 07 Uppsala, Sweden

(Received 9 May 1995 ; revised version received 16 September 1996 ; accepted 20 January 1997)

Abstract : Diurnal variation in the chemical composition of digesta and its e†ecton nutrient digestibilities of diets varying in dietary Ðbre content was examinedin pigs Ðtted with a PVTC-cannula at the terminal ileum. The pigs were fed threetimes a day (08 :00, 16 :00 and 24 :00 h). A barley control diet and four barley-based diets containing two levels (100 or 200 g kg~1 diet) of alfalfa meal or whiteclover meal and as an indigestible marker were fed according to a 5] 5Cr2O3Latin square design. In each experimental period, digesta were collected for 1 hevery third hour on each of two separate sampling days, covering in total a 24 hperiod. The concentration of dry matter (DM), crude protein (CP), ash and chro-mium (Cr) in the ileal digesta varied in relation to time of feeding. However, thepatterns were similar after all three meals (08 :00, 16 :00 and 24 :00 h) and inde-pendent of diet. The maximum DM, CP and ash contents were reached 4È5 hpost-feeding. The highest (P\ 0É05) DM concentration was found in the ilealdigesta of pigs fed the barley control diet. The DM concentration decreased(P\ 0É05) as the inclusion level of alfalfa meal and white clover meal wasincreased. The lowest DM concentration was found for the highest inclusionlevel of alfalfa meal. The ileal digestibilities of both organic matter and CP werelower 1È2 h post-feeding compared with those recorded 3È5 h later, indicatingthat the less digestible components of a diet have shorter transit times. Thepooled ileal digestibilities of organic matter and CP from the three 8 h periods(08 :00È16 :00 h, 16 :00È24 :00 h, 24 :00È08 :00 h) did not di†er (P\ 0É05) fromeach other. Therefore, the estimate of digestibility can be based on digestasamples collected from any interval between two consecutive meals. However,care must be taken to obtain representative samples of digesta between meals.

Key words : pigs, digestibility, diurnal variation, digesta Ñow, Ðbre

INTRODUCTION

Digestion at di†erent sites of the digestive tract is ofinterest to animal nutritionists attempting to improvefeed utilisation. The utilisation of nutrients di†ersdepending on the site of their breakdown and absorp-

* To whom correspondence should be addressed at : DanishInstitute of Animal Science, Department of Nutrition,Research Centre Foulum, PO Box 39, DK-8830 Tjele,Denmark.” To whom reprint requests should be addressed.

tion (Just et al 1983). Over the last two decades digestahave been obtained from pigs Ðtted with ileal cannulasin order to partition the digestion of nutrients betweenthe small and large intestine (Zebrowska 1973 ; Low etal 1978 ; Sauer et al 1980). Di†erent cannulationmethods are available and have recently been compared(Ko� hler et al 1990). Knowledge of the variation in thechemical composition of digesta is necessary if collec-tion regimes are to be planned conÐdently and if under-standing of digestive processes is to be improved. Inmost studies with cannulated pigs, digesta are collected

244J Sci Food Agric 0022-5142/97/$17.50 1997 SCI. Printed in Great Britain(

Diurnal variation in ileal digesta 245

during the day following a single meal (Sauer et al 1980 ;Knabe et al 1989) assuming no or little variation in thechemical composition of digesta between di†erentmeals. Diurnal variation in the chemical composition ofdigesta has been studied (Livingstone et al 1980 ;Graham and A- man 1986) but only with a limitednumber of diets.

The present study aimed to obtain further informa-tion on the diurnal variation in the chemical composi-tion of ileal digesta and the ileal digestibilities ofnutrients in growing pigs fed diets varying in Ðbrecontent. An additional aim was to determine if a sam-pling period following one meal was representative of a24 h sampling period.

EXPERIMENTAL

Animals

Five castrated male pigs (Large White] Landrace)with an average initial weight of 41^ 4É9 kg were Ðttedwith a post-valve T-caecum (PVTC) cannula asdescribed by van Leeuwen et al (1991). With the PVTCtechnique the caecum is replaced by a T-cannula andwhen the cannula is closed, the digesta Ñows directlyfrom the ileum into the colon. The pigs were housedindividually in 3É5 m2 smooth walled pens. Aftersurgery, the pigs were allowed 14 days to recover andregain their full appetite. Particular attention was paidto keeping the pigs washed and skin irritation was mini-mised by the liberal application of a lanolin-based zincoxide cream.

Design, diets and feeding

The pigs were fed the experimental diets according to aLatin square design (5 ] 5). Each experimental periodconsisted of 9 days of adaptation followed by a 1 daycollection of ileal digesta, 1 day of rest followed by asecond day of collection.

The formulation of the Ðve experimental diets is pre-sented in Table 1. One diet contained barley as themain ingredient. The other diets contained barley andtwo levels (100 or 200 g kg~1) of alfalfa meal or whiteclover meal. All diets were supplemented with mineralsand vitamins to meet or exceed Swedish standards forgrowing pigs. In addition was included as aCr2O3marker for measuring digesta Ñow and digestibility. Alldiets were pelleted. Diets were fed at 4% of the averagebody weight of the pigs and water was freely available.The daily dietary allocation for each pig was split intoequal portion and fed at 08 :00, 16 :00 and 24 :00 h.

Digesta collection

Digesta were collected 1 h every third hour during the 2days collection as depicted in Fig 1. Collection ofdigesta began either at 08 :00 h or at 09 :30 h on theÐrst day (day 10) and either at 08 :00 h or at 09 :30 h onthe second day (day 12) of collection for a total of 16samples per animal. During the individual collectionperiods of 1 h, the pigs were restricted in space to facili-tate the collection procedure. A soft plastic tube, 0É6 min length and 25 mm in diameter, was placed over thecannula barrel and kept in place by a plastic clampthroughout the collection period. Digesta Ñowed

TABLE 1The dietary ingredients, dietary level and the chemical composition of the experimental diets

Diet Control Alfalfa meal W hite clover meal

L ow High L ow High

Ingredients (g kg~1)Barley 950 850 750 850 750Alfalfa meal È 100 200 È ÈWhite clover meal È È È 100 200Dicalcium phosphate 20 20 20 20 20Calcium carbonate 8 8 8 8 8NaCl 4 4 4 4 4Vitamin mixture 15 15 15 15 15Cr2O3 (marker) 3 3 3 3 3

Chemical composition (g kg~1 DM)Crude protein 116 121 128 127 139Crude fat 25 23 23 24 26Starch 553 494 436 495 437Sugars 2 2 2 3 5NDF 141 171 210 162 178Ash 60 68 73 69 69

246 H JÏrgensen, J E L indberg, C Andersson

Fig 1. Scheme for the collection of ileal digesta. Diets fed at 08 :00, 16 :00 and 24 :00 h (arrows).

through the tubing into a small container which wasemptied every 10 min into a larger container packed incrushed ice. The tubing was regularly squeezed by handto aid the Ñow of digesta. At the end of each hourlycollection period the ileal digesta was weighed andfrozen at [20¡C.

Analytical methods

Prior to chemical analyses all digesta samples werefreeze-dried and ground to pass through a 1-mm meshscreen. Dry matter (DM) was determined by drying at103¡C for 16 h and ash after ignition at 550¡C for 1 h.Crude protein (CP) was estimated as Kjeldahl N] 6É25(Nordisk Metodikkommitte� 1976). Crude fat was deter-mined according to EEC method B (Larsson 1989).Starch and sugars were analysed by an enzymaticmethod (Larsson and Bengtsson 1983), and neutraldetergent Ðbre (NDF) according to Robertson and VanSoest (1981). Chromium (Cr) concentration in feed andileal digesta were determined with emission spectropho-tometry on diluted samples, using the inductivelycoupled plasma (ICP) technique, after digesting theashed samples in 85% phosphoric acid according toBock (1979).

Calculations and statistical analyses

Analysis of variance was carried out using the GLMprocedure (SAS 1985) with pig as block and period anddiet as main e†ects. The chemical concentrations of theileal digesta and the ileal digestibilities were analyzed asrepeated measures. The error term diet ] period ] pigwas used to test the e†ects of diet, period and pig in thewhole plot. Time and diet ] time were included in thesplit-plot. When signiÐcant (P\ 0É05) e†ects wereobtained, di†erences between least squares means werecompared using FisherÏs least signiÐcant di†erence pro-cedure (Milliken and Johnson 1984).

RESULTS

The pigs remained healthy throughout the experimentand no feed refusals were recorded. Of the total 400samples collected, eight were lost.

Hourly collections

There was no interaction (P\ 0É05) between diets andcollection times for the chemical composition of ilealdigesta, therefore the average values from all Ðve dietsare shown in Fig 2 together with their standard errors.Although there were di†erences (P\ 0É05) betweendiets in ileal DM and Cr concentrations at some collec-tion points, the patterns of each diet were similar. TheDM of ileal digesta ranged from 106 to 120 g kg~1fresh weight ; the lowest values were observed just afterfeeding. The pattern was the same after all three meals(08 :00, 16 :00 and 24 :00 h) independent of diet, reach-ing a maximum 4È5 h post-feeding (121È128 g kg~1fresh weight). The highest DM concentration was foundin the digesta of pigs fed the barley control diet and theconcentration dropped as the inclusion level of alfalfameal or white clover meal increased. The lowest DMcomposition was observed for the high level of alfalfa

Fig 2. Diurnal variation in the chemical composition of ilealdigesta. Mean and standard errors of dry matter (g kg~1 ilealdigesta), crude protein, ash and chromium (g kg~1 DM) of theÐve diets. Diets fed at 08 :00, 16 :00 and 24 :00 h (dashed line).

Each point is the mean of 25 observations.

Diurnal variation in ileal digesta 247

meal. The ash, CP and Cr composition of the ileal DMfollowed the same pattern as for DM in fresh digestabut reached a maximum value 1È2 h later just prior tothe next feed.

The digestibility of ileal organic matter (Fig 3) andCP (Fig 4) followed a similar pattern as observed for theCr content in ileal DM (Fig 2). The lowest digestibilitywas from 0È3 h post-feeding. The organic matter digest-

ibility reached a maximum value prior to the next feed.The average digestibilities 1È2 h post-feeding were 0É585for organic matter and 0É602 for CP, the correspondingvalues 5È6 h post-feeding were 0É658 for organic matterand 0É631 for CP. In most cases the digestibilities oforganic matter were di†erent (P\ 0É05) at di†erent col-lection times. The ileal digestibility of CP between dietswas mainly di†erent (P\ 0É05) prior to feeding. The

Fig 3. Diurnal variation in the digestibility of organic matter from cereal-based diets containing 0È200 g kg~1 alfalfa meal orwhite clover meal at the terminal ileum of growing pigs. Diets fed at 08 :00, 16 :00 and 24 :00 h (dashed line). Diets di†er at

collection time : * P\ 0É05 ; ** P\ 0É01 ; *** P\ 0É001. Each point is the mean of Ðve observations.

Fig 4. Diurnal variation in the digestibility of crude protein from cereal-based diets containing 0È200 g kg~1 alfalfa meal or whiteclover meal at the terminal ileum of growing pigs. Diets fed at 08 :00, 16 :00 and 24 :00 h (dashed line). Diets di†er at collection

time : * P\ 0É05 ; ** P\ 0É01 ; *** P\ 0É001. Each point is the mean of Ðve observations.

248 H JÏrgensen, J E L indberg, C Andersson

TABLE 2Chemical composition of ileal digesta pooled from the three 8 h between feed periods from pigs fed

diets containing 0È200 g kg~1 of alfalfa meal and white clover meala

Diet Control Alfalfa meal W hite clover meal Mean ofcollection

L ow High L ow High

Dry matter (g kg~1 fresh digesta)Collection periods08 :00È16 :00 h 127 115 103 118 109 115b16 :00È24 :00 h 125 114 103 117 113 115b24 :00È08 :00 h 131 126 112 122 116 121aMean of diets 128a 118b 106d 119b 113c

Crude protein (g kg~1 DM)Collection periods08 :00È16 :00 h 123 119 120 123 123 122a16 :00È24 :00 h 126 120 115 120 122 120a24 :00È08 :00 h 121 117 112 117 119 117bMean of diets 123 119 116 120 121

Ash (minus Cr2O3) (g kg~1 DM)Collection periods08 :00È16 :00 h 137 142 137 136 143 139a16 :00È24 :00 h 142 141 141 135 143 140a24 :00È08 :00 h 135 136 131 134 142 136bMean of diets 138 140 136 135 143

a Mean values with di†erent following letters in the same row or columns are signiÐcantly di†erent(P\ 0É05).

highest digestibilities of organic matter and CP werefound for the control diet and the digestibilitiesdecreased with increasing inclusion level of alfalfa mealor white clover meal. The lowest digestibility was foundfor the highest inclusion level of alfalfa meal, this dietalso contained the highest level of Ðbre (210 g NDFkg~1 DM).

Pooled samples

In order to compare the three 8 h collection periodsbetween meals (08 :00È16 :00 h, 16 :00È24 :00 h, 24 :00È08 :00 h) the chemical composition (Table 2) and thedigestibilities (Table 3) for the 8 h periods were pooledaccording to the amount of digesta collected. There was

TABLE 3The mean ileal digestibilities of organic matter and protein from the three 8 h feeding periods by

pigs fed diets containing 0È200 g kg~1 of alfalfa meal or white clover meala

Diet Control Alfalfa meal W hite clover meal Mean ofcollection

L ow High L ow High

Organic matter digestibilityCollection periods08 :00È16 :00 h 0É686 0É642 0É576 0É647 0É613 0É63316 :00È24 :00 h 0É702 0É642 0É501 0É650 0É617 0É62224 :00È08 :00 h 0É676 0É603 0É554 0É640 0É578 0É610Mean of diets 0É688a 0É629bc 0É544d 0É646ab 0É602c

Crude protein digestibilityCollection periods08 :00È16 :00 h 0É653 0É620 0É564 0É624 0É623 0É61716 :00È24 :00 h 0É661 0É616 0É504 0É639 0É633 0É61124 :00È08 :00 h 0É654 0É587 0É577 0É641 0É606 0É613Mean of diets 0É656a 0É608b 0É549c 0É634ab 0É621ab

a Mean values with di†erent following letters in the same row are signiÐcantly di†erent (P\ 0É05).

Diurnal variation in ileal digesta 249

no interaction (P\ 0É05) between diet and the pooled8 h collection period. The ileal digesta contained 6 gDM kg~1 fresh digesta more during the night period(24 :00È08 :00 h) than during the other two periods ofthe day (Table 2). The ileal digesta from the pigs fed thecontrol diet had the highest DM content (128 g kg~1fresh digesta) and the DM content decreased as thecontent of dietary Ðbre was increased (P\ 0É05). Therewas a lower CP and ash (minus content in theCr2O3)ileal DM during the night period. However, there wasno di†erence (P[ 0É05) between the diets.

The pooled ileal digestibilities of organic matter andCP (Table 3) from the three 8 h periods did not di†er(P[ 0É05) from each other. The ileal digestibilities ofboth organic matter and CP decreased (P\ 0É05) lin-early with increased inclusion of either alfalfa meal orwhite clover meal. The largest (P\ 0É05) decreases wereobserved for the diet containing alfalfa meal.

DISCUSSION

The chemical composition of digesta sampled from pigsÐtted with a PVTC-cannula has been shown to be lessvariable than digesta collected from pigs Ðtted with asimple T-cannula or a re-entrant cannula (Ko� hler et al1990). The re-entrant cannula is considered to providemore representative digesta samples because all of thedigesta is collected (Ko� hler et al 1990). However, prob-lems with blockage may arise when studying diets highin structural cell wall material. The PVTC-cannulaemployed in the present study had a relatively largeinternal diameter (25 mm) which permits the use ofdiets with a high Ðbre content. Cannula blockage wasnot a problem in this study and the PVTC-cannulashould provide more representative samples of digestaas indicated by a nearly complete marker recovery (vanLeeuwen et al 1991). It should also be noted that in thepresent study the pigs were allowed to move freely inrelatively large pens, except during the individual collec-tions when space was restricted to a smaller area. Thiscollection procedure is more representative of normalconditions and may also help passage of digestathrough the gastrointestinal tract (Knapka et al 1967 ;Bakker and Jongbloed 1994).

The variation in the DM concentration of ilealdigesta was similar for all Ðve diets after each of thethree meals of the day (8 h sampling periods). A similarpattern, where the highest DM concentration wasobserved 4È5 h post-feeding, has also been shown byother investigators (Livingstone et al 1980 ; Drochner1984 ; Graham and A- man 1986) when pigs were fedtwice daily. Diurnal variation in DM content of ilealdigesta following each of the diets can be related mainlyto variation in Ñuid intake as well as variation inendogenous secretions. In the present study drinking

water was freely available and therefore variation inwater intake between the diets was possible. The DMfraction of digesta consists mainly of dietary material,although digesta as a whole contains signiÐcant quan-tities of endogenous material such as pancreatic juiceand bile. These secreted endogenous sources are low inDM and the secretion is relatively continuous (Corring1980 ; Juste et al 1983 ; Hee et al 1988 ; et alJÔrgensen1992) compared to the Ñow of digesta (Zebrowska 1973 ;Low et al 1978). However, there is evidence that anincreasing amount of dietary Ðbre increases the secre-tion of endogenous material (Low 1989) which could berelated to the observed reduction in the ileal DMcontent (Table 2) with higher NDF content (Table 1).

All the diets, independent of source and Ðbre level,showed similar diurnal patterns in ileal organic matterdigestibility (Fig 3). The organic matter digestibilityvaried in the same manner as the chromium concentra-tion in the ileal DM (Fig 2). The ileal digestibility oforganic matter in the present study was considerablylower 1È2 h post-feeding compared to 4È6 h post-feeding indicating di†erent rates of passage of feed con-stituents in the gastrointestinal tract. A similar timedependent variation in ileal digestibility of DM was alsofound by Livingstone et al (1980) when feeding every12 h. Graham and A- man (1986) reported that the Ðbrecontent in ileal digesta was highest during the Ðrst hourafter feeding. As shown in the present study this coin-cides with the reduction in digestibility giving supportof the hypothesis that the less digestible components ofthe diet have a shorter transit time than the more easilydigested components. Also, in mature pigs fed twice aday, a diurnal variation in faecal concentrations ofchromium has been found. The highest concentrationbeing in the morning samples (Saha and Gilbreath1991).

The pooled 8 h digesta samples collected during thenight (24 :00È08 :00 h) had a higher (P\ 0É05) DMcontent than during the other periods (121 vs 115 g DMkg~1 ileal digesta). By contrast, Zebrowska (1973) founda lower ileal DM content during the night. However, inthe study by Zebrowska (1973), water and feed weregiven in a ratio of 2É5 : 1 and feeding was at 08 :00 h and16 :00 h. In the present study drinking water was freelyavailable at all times. The e†ect of activity of theanimals in relation to transit time of digesta on DMconcentration and digestibility is complicated in experi-ments like these. The ileal digesta is collected at shortintervals during the night. So, the animals are disturbedand more active than when they are left alone the wholenight.

The digestibilities of organic matter and CP from thethree pooled 8 h (80 :00È16 :00 h, 16 :00È24 :00 h and24 :00È08 :00 h) periods did not di†er from each other(P[ 0É05). This Ðnding was in agreement with resultsreported by Sauer (1976), Zebrowska et al (1978),Livingstone et al (1980) and Jagger et al (1992). It is of

250 H JÏrgensen, J E L indberg, C Andersson

note that no signiÐcant interactions between diets andcollection time were detected.

The results of the present study show that it is impor-tant to obtain a representative sample of digestathroughout between feed intervals. It can be concludedthat when a representative sample is obtained, a validestimate of the digestibility for a 24 h period can bebased on digesta samples collected from any 8 h inter-val between feeds.

ACKNOWLEDGEMENT

This work was supported by the Swedish Council forForestry and Agricultural Research.

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