J. Anim Sci. 2006. 84:2965-2972. doi:10.2527/jas.2006-044
© 2006 American Society of Animal Science
ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
Effects of level of feed intake on pancreatic exocrine secretions during the early postweaning period in piglets1
A. Huguet,
G. Savary,
E. Bobillier,
Y. Lebreton and
I. Le Huërou-Luron2
Unité Mixte de Recherches Systèmes d’Elevage, Nutrition Animale et Humaine, Institut National de la Recherche Agronomique, Domaine de la Prise, 35590 St-Gilles, France
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Abstract
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The objective of this study was to determine the influence of the level of feed intake and a 2-d feed restriction period on the postweaning adaptation of pancreatic exocrine secretions. At 33 d of age, 18 piglets fitted with 2 permanents catheters (for pancreatic juice collection and reintroduction) were weaned and allocated to 1 of the following 2 dietary treatments for 5 d: restricted feed allocation (restricted) or gradually increasing feed allocation (control). Pancreatic juice was collected daily during both basal and prandial periods. The basal period was defined as the period from 1400 to 1700 h (i.e., 5 to 8 h after the morning meal), whereas the prandial period was defined as the period from 30 min before to 60 min after the morning meal (given at 0900). Digestive enzyme activities and antibacterial activity were determined. Pancreatic protein secretion was 44% less (P < 0.05) in restricted piglets than in control piglets during the basal period. Trypsin secretion was affected by feed-restriction of piglets. The meal did not affect protein and trypsin secretions in restricted piglets, whereas at d 3 postweaning, protein and trypsin secretions and trypsin specific activity in control piglets were 9-, 105-, and 25-fold greater (P < 0.001) during the first 30 min after the meal than before the meal. Lipase and amylase secretions were not affected by variations in feed intake. The secretion of antibacterial activity in restricted piglets was greater (P < 0.05) than that of control piglets only at d 5. The extended feed restriction period increased the basal secretion of antibacterial activity (P = 0.09) and postprandial secretion of amylase (P = 0.05). In conclusion, a low level of feed intake during the early postweaning period decreased pancreatic protein and trypsin secretions, whereas a 2-d feed restriction period enhanced secretions of amylase and antibacterial activity. In addition, our results indicate that during periods of dietary adaptation, such as at weaning, measurements of enzyme activities in the tissue do not accurately reflect the enzyme secretion.
Key Words: antibacterial activity • digestive enzyme • feed intake • pancreatic secretion • piglet • weaning
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INTRODUCTION
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Weaning of piglets induces acute changes in both the pattern of feed intake and the composition of diet. Before weaning, most piglets have consumed very little solid feed and are unfamiliar with the starter diet. Therefore, feed intake is often very low during the first postweaning days (Brooks et al., 2001
). During this period, most of the variation in pancreatic enzyme activity measured in pancreatic tissue and in jejunal digesta has been correlated with variation in feed intake (Makkink et al., 1994; Marion et al., 2003). However, the adaptation of pancreatic enzyme secretions to variation in feed intake has not yet been evaluated. In addition, piglets having an extended feed restriction period also have a low growth rate and feed conversion efficiency during the following weeks (Bruininx et al., 2002). The extended feed restriction period potentially modifies adaptation of pancreatic digestive functions and may result in decreased digestive capacity.
Pancreatic secretion possesses antibacterial properties against many microorganisms (Rubinstein et al., 1985; Bassi et al., 1991; Pierzynowski et al., 1993a). At weaning, feed intake is the major contaminant of the small intestine, and this results in an increase of antibacterial activity secretion in pigs (Pierzynowski et al., 1992). Moreover, a 2-d feed restriction period markedly decreased the antibacterial activity secretion in cattle (Pierzynowski et al., 1992), indicating that this activity could be affected by variation in feed intake and by extended feed restriction period after weaning in piglets.
In the current study, we evaluated the influence of variation in feed intake and the effect of a 2-d feed restriction period on the postweaning adaptation of pancreatic exocrine secretions. Pancreatic enzyme secretions at basal and prandial periods as well as the pancreatic secretion of antibacterial activity were investigated in piglets the day before weaning and during the first 5 d postweaning.
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MATERIALS AND METHODS
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Animals and Dietary Treatment
The experiments were conducted under the guidelines of the French Ministry of Agriculture for Animal Research. Eighteen Pietraincross Large White x Land-race sow-reared piglets from the experimental herd of INRA (Saint-Gilles) were weaned at 33 d of age and randomly allocated to 1 of the following 2 dietary treatments for 5 d: restricted feed allocation [restricted (daily amounts of dry feed offered: 10, 10, 50, 100, and 150 g on d 1 to 5, respectively)], or gradually increasing feed allocation [control (daily amounts of dry feed offered: 50, 100, 150, 200, and 250 g on d 1 to 5, respectively)]. Body weight of the piglets was not different between dietary treatments (on average 9.2 ± 1.8 kg of BW). The feed allocation pattern of restricted piglets was designed to mimic a feed restriction period frequently observed during the first 2 d postweaning, followed by a gradual refeeding, whereas the feed allocation pattern of control piglets was a gradual increase of feed offered immediately after weaning.
No creep feed was provided during the suckling period. Weaned piglets were offered a starter wet diet (Table 1; using a 1:2 DM to water ratio on d 1 to 3, and a 2:3 ratio on d 4 and 5). Weaned piglets had access to feed for 1 h twice daily (from 0900 to 1000 and from 1800 to 1900); they had free access to water throughout the experiment. Actual feed intake was measured by weighing the feeding trough before and after the meals (Figure 1). Weaned piglets were individually housed in stainless steel, metabolic cages, which provided visual contact with each other. The room temperature was initially set at 32°C and was progressively decreased to 28°C on d 5 postweaning.
Surgical Procedure
At 28 d of age, sow-reared piglets were fitted with 2 permanent catheters (adapted from those of Le Dréan et al., 1997) under sterile conditions without antibiotics. In brief, piglets were sedated with ketamine (Imalgene, Merial, Lyon, France; 20 mg·kg of BW–1, i.m.) after a 5-h fasting period. The abdomen and the right side of the piglets were shaved and disinfected with vetedine (Vétoquinol, France). Halothane (2-bromo-2-chloro-1,1,1-trifluoromethane; Belamont, Issy Les Mouli-neaux, France) was used for general anesthesia at a rate of 2 to 3% in air supplied with oxygen (0.2 L·min–1·kg–1) throughout the surgery and given via a face mask from a closed-circuit system with spontaneous ventilation.
A 10-cm incision was made in the lateral abdomen. First, a silicone catheter (Vermed-Peters, Toulouse, France) was inserted 0.5 to 1 cm into the accessory pancreatic duct (for pancreatic juice collection) and secured with ligatures; second, a silicone catheter (Vermed-Peters) was inserted 3 to 4 cm into the duodenum (for pancreatic juice reintroduction), caudal to the accessory pancreatic duct, and fixed to the duodenum with sutures. The 2 catheters were exteriorized in close proximity to the last rib, interconnected, and placed in a bag placed that was fixed onto the back of the piglet with adhesive surgical tape. After a 3-h recovery, the piglets were returned to the sow for 4 d before pancreatic juice collection.
Pancreatic Juice Collection
Pancreatic juice was collected during basal and prandial periods. The basal period was defined as the period from 1400 to 1700 (i.e., 5 to 8 h after the morning meal), whereas the prandial period was defined as the period from 30 min before to 60 min after the morning meal (given at 0900). Pancreatic juice was collected daily during the basal period from d –1 (the day before weaning in sow-reared piglets) to d 5 postweaning, and during the prandial period from d 1 to 5. A preliminary study indicated that meals of milk from the sow did not affect the pattern of pancreatic juice and protein secretions of sow-reared piglets, which was explained by the low amount of milk intake per meal. Therefore, we did not examine the meal effects on pancreatic exocrine secretions in sow-reared piglets. In weaned piglets, pancreatic juice was collected from freely moving piglets.
At d –1, pancreatic juice was collected manually in sow-reared piglets, which were allowed to suckle during the whole sampling period. The pancreatic catheter was disconnected from the duodenal catheter and was inserted into a collection tube for 30 min. The volume of pancreatic juice secreted was measured. A constant proportion (66%) was reintroduced via the duodenal catheter into the duodenum, whereas the remainder was immediately transferred to tubes held in an ice bath. Pancreatic juice was successively collected during six 30-min periods. A pooled sample was obtained by mixing the 6 samples collected, divided into small aliquots, and stored at –20°C for later analyses. In between the sampling periods, the 2 catheters were interconnected, allowing pancreatic juice to flow toward the duodenum.
From d 1 to 5, an automatic device was designed for accurate, real-time measurement of pancreatic juice secretion, combined with collection of samples and immediate reintroduction of the remainder of the pancreatic juice into the duodenum. The automatic system was composed of 2 main elements: a juice flow detector in a small box, which was placed on the back of the piglet and connected to the pancreatic and duodenal catheters, and an integrator placed outside the cage and connected to the juice flow detector.
Briefly, pancreatic juice flowed into a storage device of 20 ± 2 µL capacity. When 2 electrodes placed at opposite sides of the storage device were in contact with the pancreatic juice, a signal was generated, driving a peristaltic pump that reintroduced all (between sampling periods) or part (66%) of the pancreatic juice into the duodenal catheter. The remainder (33%) of the pancreatic juice was collected in a tube held in an ice bath. Simultaneously, the signal was transmitted to a computer and converted to a flow value. The software operating the device was developed with LabVIEW (National Instruments, Austin, TX). During basal periods, pancreatic juice was successively collected during six 30-min periods. A pooled sample was obtained by mixing the 6 samples collected. During prandial periods, pancreatic juice was successively collected during three 30-min periods, from 30 min before to 60 min after the morning meal. Pancreatic juice samples were divided into small aliquots and stored at –20°C until analyses.
Quantifying Antibacterial Activity
The antibacterial activity of the pancreatic exocrine secretion was analyzed using the microtiter broth method adapted from Holowachuk et al. (2004). One unit (U) of antibacterial activity was equivalent to the antibacterial activity of 1 µg of gentamicin. Pancreatic juice samples were sterilized with a membrane filter (0.22 µm pore size; Fisher, Elancourt, France). Serial 2-fold dilutions of a sterile gentamicin solution (10 mg·mL–1; Sigma, Lyon, France) were prepared using sterile PBS [NaCl (130.90 mM), Na2HPO4 (8.94 mM), NaH2PO4 (0.83 mM), KH2PO4 (1.55 mM); pH 7.4]. Escherichia coli strain ATCC 25922 (LGC Promochem, Molsheim, France) was used as standard bacteria for determination of antibacterial activity (Kruszewska et al., 2004). An overnight growth of the strain [at 37°C in sterile Mueller-Hinton broth (MHB); pH 7.4, Oxoid, Dardilly, France] was diluted with MHB to a final density of 1 x 104 cfu/mL.
Assays were performed in sterile U-shaped, 96-well polypropylene microtiter plates (Dutscher, Brumoth, France). Sterile PBS (50 µL) and MHB (100 µL) were pipetted into 2 wells in the first column (sterility controls). Two adjacent wells received sterile PBS (50 µL) and the bacterial suspension (100 µL; growth controls). After adding the bacterial suspension (100 µL), the remaining wells were filled in duplicate with different concentrations of gentamicin (50 µL) ranging from 2.5 to 0.625 µg·mL–1 to generate a standard curve for bacterial growth inhibition, or with pancreatic juice samples (tests samples, 50 µL).
The plates were sealed with breathable membranes (Sigma) and incubated at 37°C for 24 h. The optical density of each well was measured at 562 nm (OD562) every 2 h with a microtiter plate reader (Argus 300, Packard, Houston, TX). Plates were automatically shaken for 15 s before each OD562 reading. The initial OD562 was subtracted from the values obtained during incubation, yielding net OD562. Net OD562 vs. time was plotted, and the area under the growth curve for each well was calculated using a program developed with Labview software. A standard curve was established from the area under the growth curves of the gentamicin standards and growth controls and used to express the antibacterial activity of pancreatic juice samples.
Protein and Enzyme Activity Assays
Protein concentration was measured according to Lowry et al. (1951) using BSA as a standard. Trypsin (EC 3.4.21.4) activity, which is the main proteolytic enzyme activity in pancreatic juice after weaning, was measured after activation, according to Lainé et al. (1993), using N-
-benzoyl-L-Arg-p-nitroanilide as the substrate. Lipase (EC 3.1.1.3) and amylase (EC 3.2.1.1) activities were determined as described previously (Le Huërou et al., 1990). The resulting enzymatic units were calculated as nanomoles of substrate hydrolyzed per minute and are reported as IU. Secretion of enzyme activity was expressed as international units per hour, and enzyme specific activity was expressed as international units per milligram of pancreatic protein–1.
Statistical Analyses
Analyses of variance were performed using the GLM procedure (SAS Inst. Inc., Cary, NC). Because of the high variability in pancreatic variables (juice flow expressed as mL·h–1, protein secretion expressed as mg·h–1, enzyme secretion and specific activity expressed as IU·h–1 and IU·mg of protein–1, respectively, and antibacterial activity secretion expressed as U·h–1) between animals, relative values were calculated and analyzed. Within piglet, daily data obtained during both basal and prandial periods were expressed relative to the value measured at d –1. Statistical analyses were performed for these relative values. The effect of dietary treatment on the variables measured during basal periods was tested using the residual variation between piglets as error, and the effects of day and dietary treatment x day interaction were also tested. The effect of dietary treatment on the variables measured during prandial periods was tested within each day using the residual variation between piglets as error, and the effects of meal and dietary treatment x meal interaction were also tested. Moreover, ANOVA using GLM was performed to examine the effect of the feed restriction period during the first 2 d postweaning. From d 3 to 5, the effect of dietary treatment was evaluated on variables using the level of feed intake as a covariate. When an effect was (P < 0.05) or tended to be (P < 0.1) significant, adjusted least square means (lsmeans) were compared using a t-test. Values presented are lsmeans ± SEM. Differences were declared significant at P < 0.05, and tendencies (P < 0.1) were included.
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RESULTS
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Pancreatic Exocrine Secretions in Sow-Reared Piglets
In our experimental conditions, sow-reared piglets had access to the sow’s teat throughout the day and sucked on average 20 times per day. Therefore, because of the frequent feeding and (subsequently) the relatively low milk intake per sucking, kinetics of pancreatic juice, protein, and enzyme secretions were not affected by consumption of milk from the sow (data not shown). In sow-reared piglets, the average pancreatic juice volume, protein, trypsin, lipase, and amylase secretions were 4.2 ± 2.1 mL·h–1, 8.8 ± 6.8 mg·h–1, 687.5 ± 1,076 IU·h–1, 115.4 ± 75 kIU·h–1, and 131.9 ± 78.8 kIU·h–1, respectively. The average trypsin, lipase, and amylase specific activities were 103.3 ± 154.3 IU·mg–1 of protein, 22.2 ± 29.7 kIU·mg–1 of protein, and 19.5 ± 12.2 kIU·mg–1 of protein, respectively. The average antibacterial activity secretion was 3.0 ± 1.6 U·h–1.
Effects of Weaning and of Variation in Feed Intake on Basal Pancreatic Exocrine Secretions
As expected, after a growth pause immediately post-weaning, BW gain of control piglets was positively increased. There was no significant dietary treatment x day interaction on the studied variables, except for the secretion of antibacterial activity. Daily protein, trypsin, lipase, and amylase secretions, but not the volume of pancreatic juice secreted, increased after weaning (Table 2). Compared with sow-reared piglets, secretions were 7-fold (P < 0.001), 49-fold (P < 0.005), 1.6-fold (P < 0.05), and 2-fold (P < 0.001) greater at d 5, respectively. Lipase and amylase specific activities were decreased after weaning, being respectively 80 and 70% less (P < 0.001) at d 5 than at d –1.
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Table 2. Relative pancreatic juice volume, and protein, trypsin, lipase and amylase secretions and specific activities in restricted piglets (R) or control piglets (C) from the preweaning day (d –1) to 5 d postweaning (d 1 to 5) during basal periods1,2
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Dietary treatment affected the pancreatic protein secretion throughout the experimental period. Protein secretion was 44% less (P < 0.05) in restricted piglets than in control piglets.
The dietary treatment x day interaction was significant for the secretion of antibacterial activity (Figure 2). In control piglets, secretion of antibacterial activity was not modified by weaning regardless of day, whereas in restricted piglets it was 2.9-, 2.6-, and 5.1-fold greater (P < 0.05) at d 1, 2, and 5, respectively, compared with d –1. Daily values measured in restricted piglets were greater (P < 0.05) than those measured in control piglets only at d 5.
Effects of Weaning and of Variation in Feed Intake on Pancreatic Exocrine Secretions During the Meal Response
The meal effect was evaluated during the preprandial (–30 to 0 min before the meal) and postprandial (0 to 30 min and 30 to 60 min after the meal) periods for protein, trypsin, and amylase secretions. For lipase secretion, the meal effect was evaluated during the preprandial (–30 to 0 min before the meal) and postpran-dial (only 0 to 30 min after the meal) periods. There was no dietary treatment x meal interaction on the studied variables, except for protein and trypsin secretions at d 2 and 3.
There was no meal effect at d 1 (data not shown) due to the very low level of feed intake at the first postweaning meal (Figure 1
). The pancreatic juice volume was not affected by the meal throughout the experimental period (data not shown). Compared with pre-prandial values, postprandial protein secretions were increased at d 3, 4, and 5 (Figure 3). At d 3, the meal did not markedly affect protein secretion in restricted piglets; in contrast, during the first 30 min after the meal, it was 9-fold greater (P < 0.001) than before the meal in control piglets. At d 4, there was no effect of dietary treatment, and protein secretion was on average 4-fold greater (P < 0.005) during the first 30 min after the meal than before the meal. Trypsin secretion followed the same pattern for the meal response as protein secretion (Figure 3). In restricted piglets, there was no meal response throughout the experimental period, whereas in control piglets at d 2 and 3, meal induced on average a 23- and 81-fold increase (P < 0.05), respectively, during the postprandial hour. At d 4 and 5, there was no effect of dietary treatment. There was no effect of dietary treatment on lipase and amylase secretions throughout the experimental period (Figure 3). Compared with preprandial values, lipase secretions were on average 2.0- (P = 0.07), 2.5- (P < 0.05), and 1.8-(P = 0.09) fold greater at d 3, 4, and 5, respectively, during the first 30 min after the meal. Meal did not affect amylase secretions.
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Figure 3. Relative values of protein, trypsin, lipase, and amylase secretions on d 1 to 5 after weaning in restricted piglets ( ) or control piglets ( ) during prandial periods (from 30 min before to 60 min after the meal) at d 2, 3, 4, and 5 postweaning. Within piglet, daily data were reported relative to the value measured at d –1. In sow-reared piglets, average values were 8.8 ± 6.8 mg·h–1, 687.5 ± 1,076 IU·h–1, 115.4 ± 75 kIU·h–1, and 131.9 ± 78.8 kIU·h–1, respectively, for pancreatic protein, trypsin, lipase, and amylase secretions. Relative values are least square means (lsmeans) ± SEM. a–cWithin a day, for a dietary treatment x meal interaction (P < 0.1), lsmeans without a common superscript letter differ (P < 0.05). x,yWithin a day, when the meal effect was significant (P < 0.1), lsmeans without a common superscript letter differ (P < 0.05).
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Effects of an Extended Feed Restriction Period on Pancreatic Exocrine Secretions
The effect of the extended feed restriction period on pancreatic variables during the d 3 to 5 postweaning period was tested using the level of feed intake as a covariate. In this way, the effect of the extended feed restriction period was evaluated between the 2 groups of piglets at a similar postweaning age. Analysis was performed on both basal and postprandial values. When the level of feed intake was adjusted, postprandial amylase secretion and basal antibacterial activity secretion were 400% (P = 0.05) and 600% (P = 0.09) greater, respectively, in restricted piglets compared with control piglets (data not shown). The other variables of the basal and postprandial periods were not affected by a 2-d feed restriction period.
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DISCUSSION
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The different in vivo methods used for pancreatic juice collection in experimental animals are mainly adapted from the technique developed by Routley et al. (1952), as reviewed by Kato et al. (1999). It allows the collection of pure, nonactivated pancreatic juice that is reintroduced into duodenum distally to the pancreatic duct. Pancreatic juice can be collected up to 2 or 3 mo in catheterized animals. However, in most experiments performed in pigs, pancreatic juice was not at all (Pierzynowski et al., 1988b, 1990) or only partially reintroduced into duodenum after a relatively long time delay (on average 1 h after secretion; Rantzer et al., 1997; Lesniewska et al., 2001), leading to changes in the secretion patterns of pancreatic juice, protein, and enzymes (Corring, 1974; Pierzynowski et al., 1988a; Houe et al., 1997). Moreover, the pancreatic juice volume reintroduced was fixed and not in proportion to the volume secreted. The consequence could be an inadequate reintroduction of pancreatic enzymes for optimal nutrient digestion. In the current study, the automatic device developed was designed to immediately reintroduce the pancreatic juice of the piglet in a constant proportion to the volume secreted, simulating physiological conditions. Because of the automatic collection and reintroduction, human attendance was reduced, and therefore stress induced by manipulation of piglets during juice collection and reintroduction was minimized.
In sow-reared piglets, our results are in agreement with values reported by Rantzer et al. (1997) in sow-reared piglets of similar age (3.7 ± 0.4 mL·h–1 and 10.6 ± 1.2 mg·h–1 for juice volume and protein secretion, respectively). After weaning, the gradual refeeding involves well-described increase of pancreatic digestive enzyme secretions at basal and prandial periods (Pierzynowski et al., 1993b, 1995; Rantzer et al., 1997). In the current study, results on pancreatic variables measured during the first postweaning week were largely in agreement with these literature data. It is noteworthy that the pattern of trypsin secretion adaptation to weaning contrasts with that of lipase and amylase. Compared with sow-reared piglets, ratios of trypsin/ lipase and trypsin/amylase secretions were 75- and 50-fold increased, respectively, at d 5 postweaning as a result of a decrease in lipase and amylase specific activities (by 80 and 70%, respectively) associated with a sharp increase in trypsin specific activity (by 1,400%). These modifications in the hydrolytic capacities are in agreement with those reported in the pancreatic tissue. Two weeks after weaning, trypsin specific activity was equal or even 170 to 316% greater than that measured in suckling piglets when lipase specific activity was 80% depressed (Owsley et al., 1986; Jensen et al., 1997; Marion et al., 2003). Adaptation of trypsin and lipase specific activities can be related to modification in the composition of the weaning diet. The transition from maternal milk rich in lipids to a weaning diet with relatively low fat content and rich in complex plant proteins induces adaptation of trypsin and lipase secretions to amounts of their respective substrate in the diet as reported in growing pigs (Corring and Saucier, 1972; Corring et al., 1982, 1984). It is notable that results from our study and of Lesniewska et al. (2001) did not record any increase in the amylase specific activity during the first postweaning week, although the starter diet contained a high amount of starch. Accordingly, amylase activity measured in pancreatic tissue was 7 to 16% less 2 wk after than before weaning (Owsley et al., 1986; Jensen et al., 1997). Adaptation of pancreatic amylase to dietary changes seems to take a longer time than for trypsin. In growing pigs, adaptation of amylase to the amount of dietary starch occurred only after a delay of 5 to 7 d (Corring, 1980).
Our results indicated that the postweaning adaptation of protein and trypsin secretions in response to the meal depended on the level of feed intake. In restricted piglets, postprandial pancreatic protein and trypsin secretions did not increase, whereas a sharp augmentation was observed in control piglets. Consequently, values in restricted piglets were on average 73 and 82% lower, respectively, during the first 30 min after the meal (from d 2 to 5) than in control piglets. This is in agreement with both the lower level of trypsin content in jejunal digesta and the greater level of trypsin activity in pancreatic tissue reported in weaned piglets with restricted feed allocation (Makkink et al., 1994; Marion et al., 2003). With restricted feed allocation, amounts of substrates in the intestinal lumen are too low to efficiently stimulate pancreatic trypsin secretion (Di-Magno et al., 1973) resulting in a poor diminution of enzymes stored into acinar cells. Among gastrointestinal hormones, cholecystokinin and gastrin, well known as stimulants of pancreatic protein and trypsin secretions (Lhoste et al., 1995; Evilevitch et al., 2003), may mediate adaptation of pancreatic trypsin secretion to feed intake level. Indeed, a previous study described a correlation between plasmatic concentrations of cholecystokinin and gastrin with the level of feed intake during the first postweaning week (Marion et al., 2003).
In our study, adaptation of lipase secretion did not depend on the level of feed intake. In contrast, it seems that amylase secretion was slightly influenced by the level of feed intake, particularly at d 5. The increase in postprandial amylase secretion in restricted piglets (by 53% at d 5) compared with control piglets is in agreement with the 70% decrease in amylase activity stored in the pancreatic tissue of weaned piglets with 7-d restricted feed allocation (Marion et al., 2003). In addition, our results indicated that the 2-d feed restriction period resulted in a 400% increase in postprandial amylase secretion during the d 3 to 5 postweaning period. These results confirm an atypical adaptation of amylase secretion in response to variation in feed intake during the early postweaning period. Disturbed peptidase activity in the small intestine was also reported in weaned piglets restricted-fed the first 2 d postweaning (Marion et al., 2005). Opposite patterns between the postweaning secretion of amylase and the amount of dietary starch intake do not agree with positive correlations reported in growing pigs (Jakob et al., 1999). The physiological significance as well as the identification of regulatory mechanisms involved in amylase secretion requires further investigations.
To our knowledge, no previous study documented the pancreatic secretion of antibacterial activity during the early postweaning period. It has been reported to be 10-fold increased 2 wk postweaning (Pierzynowski et al., 1992). In contrast, in our experimental conditions, weaning did not modify the secretion of antibacterial activity during the first 5 d postweaning in control piglets, whereas it was increased in restricted piglets, resulting in 400% greater values at d 5 postweaning compared with d –1. In addition, the 2-d feed restriction period enhanced by 600% the secretion of antibacterial activity during d 3 to 5 postweaning period compared with control piglets. This increase may be a compensatory phenomenon in maintaining bacterial homeostasis in the small intestine. Indeed, at this time period, the small intestine is presented with new bacteria and has not yet developed an effective system of defense (Pierzynowski et al., 1992; Thacker, 1999). Moreover, the invasion risk of the gut by pathogens is greater during a feed restriction period or between meals (Holowachuk et al., 2004). However, the compensatory phenomenon seems insufficient to prevent diarrhea in piglets with low level of feed intake during the early postweaning period (Madec and Josse, 1983). The regulatory mechanism of the secretion of antibacterial activity has not been established but seems to be independent of that of pancreatic juice and protein secretions, according to Pierzynowski et al. (1992) and Holowachuk et al. (2004).
Taken together, our results indicate that pancreatic adaptation to weaning is very specific for each enzyme and can be summarized as a sharp augmentation of trypsin secretion and a moderate increase in lipase and amylase secretions. In piglets with low level of feed intake, protein and trypsin secretions were reduced, whereas that of antibacterial activity was stimulated. An extended feed restriction period sharply enhanced secretions of amylase and antibacterial activity. The physiological significance of variations in amylase and antibacterial activity secretions remains to be elucidated.
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Footnotes
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1 Supported by a grant from the European Union (EU project QLK5-CT-2000-00522). The authors are solely responsible for the work described in this article, and their opinions are not necessarily those of the European Union. 
2 Corresponding author: Isabelle.Luron{at}rennes.inra.fr
Received for publication January 25, 2006.
Accepted for publication June 15, 2006.
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Abstract
INTRODUCTION
