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Department of Animal Science and Animal Health, Division of Animal Nutrition, Royal Veterinary and Agricultural University, DK-1870 Frederiksberg, Denmark and * U.S. Department of Agriculture/ARS Childrens Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030
2To whom correspondence should be addressed. E-mail: psa{at}kvl.dk.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • colostrum • immunoglobulin • disaccharidase • peptidase • intestinal closure • piglets
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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).
The large neonatal mortality in farm animals (e.g., 10–20%) (2
) indicates that the neonate often fails to adapt adequately, and in modern pig production, an increase in average litter size has further increased the risk for newborn piglets to die from starvation and lack of passive immunity. Rearing of piglets by surrogate mothers and the use of milk replacers (MR) have been employed to increase neonatal survival. It remains essential, however, that newborn piglets receive porcine Ig to achieve a sufficient degree of passive immunization. The use of bovine colostrum or MR for newborn pigs, without porcine Ig, is associated with reduced survival (3
–5
). Even when purified porcine Ig or plasma protein (including Ig) is added, passive immunization might be low because intestinal macromolecule absorption is greatly influenced by the composition of the fluid in which they are dissolved (6
,7
). There is no information on the efficiency of Ig absorption from plasma fed to newborn pigs, although plasma products have been widely used to improve digestibility and growth in weanling pigs (8
,9
).
In addition to its immunological role, colostrum has a marked stimulating effect on the growth and maturation of the neonatal gastrointestinal tract (10
–13
). Exposure to colostrum has specific effects on the processing of some brush border enzymes in neonatal pigs, such as lactase-phloridzin hydrolase, and this may affect the luminal hydrolytic activity (14
,15
). Artificial diets seem less efficient than colostrum in stimulating intestinal growth and function in newborn pigs (15
,16
). Diet-dependent effects could be most pronounced during the perinatal period when colostrum induces some fundamental changes in the enterocyte membrane in association with the endocytotic uptake of protein macromolecules (17
,18
). Few studies in neonatal pigs have followed the effects of different diets on intestinal function beyond the Ig absorption period (lasting 
24 h).
In the present experiments, we investigated the extent to which porcine colostrum (PC) was superior to bovine colostrum (BC), porcine plasma (PP) and a MR in stimulating intestinal uptake of protein macromolecules and enzyme activity in neonatal pigs. The objective of Experiment 1 was to compare the effect of feeding PC, BC, PP or porcine milk (PM) on intestinal absorption of IgG and a macromolecule marker, bovine serum albumin (BSA). In Experiment 2, macromolecule absorption was investigated in three groups of pigs fed PC, a mixture of BC and PP or a MR. In this experiment we also tested whether PC was superior to the two colostrum substitutes in mediating intestinal growth and stimulating enzyme activity.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Experiment 1. Porcine colostrum was collected manually from a number of sows (Large White x Landrace, Research Station Sjælland III, Denmark) within 6 h of birth. Porcine milk was collected from a number of lactating sows at 1–3 wks postpartum. Bovine colostrum was collected from a number of different Holstein Friesian dairy cows from the first milking after parturition. Plasma was collected after centrifugation (3000 x g for 12 min at 4°C) of blood obtained from slaughter pigs at a local slaughterhouse. Pooled PC, BC, PM and PP were stored in lots at -20°C.
A total of 23 crossbred newborn pigs (Large White x Danish Landrace, Sjælland III) were obtained from two sows immediately after spontaneous birth and before suckling. Piglets from each litter were allocated to receive PC (n = 5), BC (n = 6), PM (n = 6) or PP (n = 6). Mean body weight at birth was 1.36 ± 0.09 kg and did not differ among the four treatment groups. The pigs were housed together, provided with straw bedding and kept warm by an electric heater. The piglets were fed 15 mL/kg body using an orogastric tube (infant feeding tube 8F, PharmaPlast, Lynge, Denmark) starting at 4–5 h after birth (time 0) and ending at 12 h. The feed was heated to 30°C before feeding. At the second feeding (3 h), all piglets were administered a diet containing the macromolecule marker, BSA (50 g/L, A-4503; Sigma Chemical, St. Louis, MO). Blood samples (2 mL) were collected from the vena jugularis using heparinized syringes immediately before feeding at 3, 6, 9 and 12 h and transferred to ice-chilled EDTA glass tubes. The blood samples were centrifuged (4000 x g for 8 min at 4°C) and plasma was stored at -20°C until biochemical analyses. After the experiment, the piglets were returned to their mothers. The National Committee on Animal Experimentation, Denmark, approved all the animal experiments.
Experiment 2.
A total of 23 crossbred newborn pigs (Large white x Danish Landrace, Sjælland III) were obtained from two sows by caesarean section at term (115 d gestation). Caesarean section was performed 22 h after induction of parturition by prostaglandin F2
(175 µg, intramuscularly, cloprostenol, Estrumate, Pitman-Moore, Harefield, UK) to mimic the normal metabolic and endocrine changes in the fetus and sow associated with spontaneous delivery at term (19
,20
). The pigs were assigned to a newborn group (n = 5) or to receive PC (n = 6), BC containing PP (BCP, n = 6) or MR (n = 6) for 2 ds after birth. All piglets from the three fed groups were fitted with an orogastric tube (infant feeding tube 6F, PharmaPlast) for enteral feeding. To prevent the pigs from chewing the feeding tube, it was passed through the cheek and secured to the skin with sutures. Each piglet was also fitted with a vascular catheter (infant feeding tube 4F, Portex, UK), inserted into the dorsal aorta via the umbilical cord. The catheter was sutured to the cord and skin at 3–4 places. To prevent continuous bleeding from the cord, it was ligated with a soft cotton thread. Finally, a tight cotton body suit was fitted onto each pig to protect the catheters. All piglets were kept individually in infant incubators (Air-Shields, Hatboro, PA).
PC, BC and PP were collected as described for Experiment 1. BC was mixed with freeze-dried PP and raw bovine milk cream, in the proportion 45:40:15, respectively, such that it had concentrations of energy (6768 kJ/L) and protein (144.8 g/L) that were similar to those measured in the PC pool (6800 kJ/L and 146.5 g/L, respectively). The BC mixture was stored in small lots at -20 oC until use. The MR was made of three commercial products used for feeding infants 0–2 y of age (per L water: 80 g Pepdite 0–2, 70 g Maxipro and 75 mL Liquigen-MCT, all products kindly donated by SHS International, Liverpool, UK). The contents of macronutrients were as follows (per L solution): energy, 4140 kJ; protein (mainly whey protein concentrate), 67 g; carbohydrate (mainly glucose), 45 g; sodium, 0.30 g; potassium, 0.64 g; calcium, 0.59 g; and phophorus, 0.42 g. The energy and protein concentrations of the milk replacer were designed to match those of sow’s milk (21
). Because we wanted to study the effect of a MR diet independent of the presence of luminal Ig, no plasma proteins were included in this diet. To provide the MR pigs with some immunological protection, doses of 5 and 9 mL of maternal plasma per pig were injected at 6 and 12 h after birth, respectively, via the arterial catheter. This plasma was produced aseptically from centrifuged maternal blood (3000 x g for 15 min at 4°C), collected from a maternal uterine vein at the time of the caesarean section.
Each piglet was fed 15 mL/kg every 3 h via the orogastric tube until tissue collection 45–48 h after the first feeding. At feeding time 0 (4–5 h after birth), BSA was included in the feed as a macromolecule marker (20 g/L, A-4503, Sigma), and at time 12 h, human serum albumin (HSA) was included as a marker (20 g/L, A-1653, Sigma). Arterial blood samples were taken from the pigs via the vascular catheter at the following time points before feeding: 0, 1.5, 3, 6, 9, 12, 13.5, 15, 18 and 21 h. Finally, a blood sample was taken when the pigs were killed for tissue collection (anesthesia with sodium pentobarbitone, 200 mg/kg, intravenously). Plasma was prepared and stored for later biochemical analyses as described for Experiment 1.
Macromolecule measurements
Concentrations of porcine IgG (pIgG), bovine IgG (bIgG), BSA and HSA were determined by rocket immunoelectrophoresis (7
,17
,22
). Four different monospecific antisera, raised against BSA, HSA, pIgG and bIgG in rabbits, were used in the electrophoresis assays (BSA: Z-0229, DAKO, Copenhagen, Denmark; HSA: A-0001, DAKO; bIgG: Z-0247, DAKO; pIgG: A226/RH, Biogenesis, Poole, UK). The standards used for measuring BSA and HSA were the same as those used for the feed solutions. The standards used to measure pIgG and bIgG were obtained from DAKO (pIgG: X-0906) and Sigma (bIgG: I-5506).
Tissue collection
For all pigs in Experiment 2, the small intestine, from the pyloric sphincter to the ileocolonic junction, was rapidly removed by cutting along the mesenteric border, weighed and its length recorded in a relaxed state. The intestine was removed to an ice-cold metal plate and divided into three segments of equal length, designated proximal, middle and distal regions. From the middle of each region, a 2- to 3-cm piece was frozen in liquid nitrogen and kept at -80°C for later enzyme analyses. Another 2- to 3-cm piece was fixed in Carnoy’s fluid for 6–8 h and transferred to 70% ethanol for later histological examination. Finally, a 10-cm segment was removed from each intestinal region to measure intestinal dimensions. This segment was slit along its length for measurement of the percentage of mucosa removed by gentle scraping with a glass slide. The proportion of mucosa was determined on a dry matter basis after drying both the mucosa and the muscularis layers at 50°C for 72 h. The stomach and pancreas and a series of other internal organs (heart, kidney, liver, lungs, adrenals, spleen) were also removed and their wet weights recorded.
Intestinal morphology
Samples of fixed intestine from the proximal and distal regions were embedded in paraffin, sectioned (5 µm) and stained with hematoxylin and eosin. The mean villous height, crypt depth and intestinal circumference were quantified by an observer who was unaware of the sample source using a Axiophot microscope (Carl Zeiss, Oberkochen, Germany) and NIH image software version 1.60 (U.S. NIH, Bethesda, MD) in at least 15 vertically well-oriented villus-crypt columns.
Enzyme analyses
Frozen tissue from each of the three intestinal regions was homogenized in 1.0% Triton X-100 and the homogenates assayed for disaccharidase and peptidase activities (23
). Sucrose (0.01 mol/L; no. 194018, ICN, Aurora, OH) and lactose (0.12 mol/L; L-3625, Sigma) dissolved in sodium maleate buffer (50 mmol/L, pH 6.0) were used as substrates for sucrase-isomaltase (EC 3.2.1.48–10) and lactase-phloridzin hydrolase (EC 3.2.1.23–62), respectively. Maltose (0.0112 mol/L; L-5885, Sigma) was used to measure maltase activity, which represents the combined activity of maltase-glucoamylase (EC 3.2.1.20) and sucrase-isomaltase. Aminopeptidase N (EC 3.4.11.2), dipeptidyl peptidase IV (EC 3.4.14.5) and aminopeptidase A (EC 3.4.11.7) activities were measured using three peptidase-specific substrate solutions, i.e., 10 mmol/L L-alanine-4-nitroanilide (Merck, Darmstadt, Germany) in 50 mmol/L Tris-HCl, pH 7.3, 15 mmol/L glycyl-L-proline-4-nitro-anilide (Bachem, Bubendorf, Switzerland) in 50 mmol/L Tris-HCl, pH 8.0 and 10 mmol/L -L-glutamic acid 4-nitroanilide (synthesized at the Institute of Protein Chemistry, Hørsholm, Denmark) in 50 mmol/L Tris-HCl, pH 8.0, respectively. Activity was expressed per gram of wet intestinal tissue, and one unit of activity (U) represented 1 µmol of substrate hydrolyzed/min at 37°C.
Data analyses
All values presented in text and figures are means ± (SEM), with n as the number of pigs. The absorptive efficiency (%) of the two macromolecule markers (BSA and HSA) was calculated as the total amount present in plasma at the time of maximal concentration divided by the total intake. A plasma volume of 68 mL/kg body was assumed in the calculations (24
). The metabolic clearance of macromolecules was neglected in the calculations. For blood values (plasma IgG, BSA, HSA), the effects of treatment were evaluated using a linear model and the MIXED procedure of SAS (25
) with sample time as the repeated measure. For the tissue values (enzyme activities), the effects of treatment, region (proximal, middle, distal) and treatment x region interaction were tested using the GLM procedure (25
) with the pig (nested within treatment) as the experimental test unit. Significant differences among means (P < 0.05) were detected by the Duncan’s Multiple Range test (25
).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Immunoglobulin absorption.
The concentrations of pIgG (g/L) in the four diets were 73.5 (PC), 0.0 (BC), 0.8 (PM) and 29.7 (PP). Analyzed across the three sample times at 6–12 h after the first meal, the plasma pIgG level was significantly elevated in PC vs. PM and PP pigs (Fig. 1A
). The level of pIgG measured in the two last-mentioned groups (1–3 g/L), however, remained significantly higher than the level in BC pigs (<0.3 g/L).
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50% 9 h after BSA intake (Fig. 1B
). Relative BSA absorption in BC pigs was 30% and significantly lower than in PC pigs. In PM and PP pigs, the proportions of absorbed BSA were similar, and both were lower than in the PC and BC groups (18–20%, Fig. 1B
). Experiment 2
Immunoglobulin absorption.
Concentrations of pIgG in the PC and BCP diets were 52.2 and 13.2 g/L, respectively. The concentration of bIgG in the BCP diet was 47.5 g/L. Analyzed across sample times, the pIgG concentration in plasma was significantly different among the three treatments with the highest value in PC piglets and the lowest in MR pigs (Fig. 2A
). The pIgG in the MR group (maximum 3.0 ± 0.3 g/L at 13.5 h) originated from the injection of porcine serum (see Materials and Methods) rather than uptake of Ig from the MR. In the BCP piglets, a significant increase was observed over time for both plasma pIgG (Fig. 2A
) and bIgG (data not shown). Absorption of bIgG increased until 15 h; at that time, the concentration (5.0 ± 0.6 g/L) was similar to that of pIgG (5.4 ± 0.7 g/L, Fig. 2A
). The percentage of absorbed porcine IgG 3 h after the first meal was 22.6 ± 2.3% in the PC piglets. Correspondingly, the percentage of absorbed porcine and bovine IgG in the BCP group was 7.0 ± 3.0 and 3.3 ± 1.2% at 3 h.
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). At 0–9 h after BSA ingestion, plasma BSA increased significantly in both of the colostrum groups, but faster in the PC than in the BCP group. Plasma BSA also increased in the MR group, although the values remained much lower than in the other two groups. At the time of maximal plasma BSA levels, 29.2 ± 2.7, 23.4 ± 3.0 and 7.7 ± 1.3% of the administered BSA had been absorbed in the PC, BCP and MR groups, respectively. When HSA was included into the meal at 12 h, the relative absorption of HSA (measured at 18 h) in the PC group was similar (22.7 ± 4.7%, Fig. 2C
) to that of BSA for this group (29.2 ± 2.7%, Fig. 2B
). In contrast, the relative absorption of HSA in the BCP and MR groups was significantly lower (5.0 ± 0.6 and 1.7 ± 0.9%, respectively, Fig. 2C
) than the corresponding values for BSA (Fig. 2B
).
Organ weights and intestinal morphometry.
At the end of the 2-d protocol, there were no differences in body weight among the three fed groups (mean 1.41 ± 0.08 kg), and the mean body weights were only slightly (and not significantly) greater than those at birth. In contrast, significant increases occurred in the weights of the stomach (+31%, P < 0.05), pancreas (+81%, P < 0.001) and small intestine (+75%, Fig. 3A
, P < 0.0001), and in intestinal length (+ 30%, Fig. 3B
, P < 0.01) in all three groups from birth to 2 d. Because the proportion of dry mucosa also increased (+28%, Fig. 3C
, P < 0.001) there was a total increase in the mucosal mass of +123% from birth to 2 d of age. The mean values of these gut growth parameters did not differ among the groups of pigs fed PC, BCP or MR.
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and C
, average values across the proximal and distal intestine) in the three fed groups did not differ significantly from those in newborn pigs. There was no significant effect of intestinal region (proximal, distal) on the intestinal growth parameters. Figure 5
shows representative micrographs of the mucosal histology for the four treatment groups (proximal intestine). In the two colostrum groups (PC and BCP, Fig. 5B
and C
), the epithelium and its vacuolated cells showed diffuse protein staining as a result of the uptake of intact colostral proteins. In contrast, the epithelium from pigs fed MR (Fig. 5D
) contained enterocytes with largely empty vacuoles. Crypt depth increased significantly from birth to 2 d in the BCP and MR groups, but not in the PC group (Figs. 4B
and 5
).
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Enzyme activities.
For each enzyme, the mean activity per gram of tissue for the proximal, middle and distal intestine was calculated, and the results are presented in Figures 6
and 7. Analyzed across the three fed groups, there were significant effects of treatment for all measured enzyme activities, except that of dipeptidyl peptidase IV. There was also a significant treatment x region interaction for all six enzyme activities, except lactase activity.
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). In contrast, maltase activity was highly elevated in the BCP group compared with the other three treatment groups (Fig. 6B
). The increase in maltase activity in the BCP pigs was most pronounced in the middle and distal part of the small intestine (9-fold increase relative to newborn pigs). A pronounced increase also occurred in the PC pigs compared with newborn pigs (1.5-fold, P < 0.001 as tested by Student’s t test). Due to a large variation in maltase activity within the BCP group, this increase did not show up in the total treatment group comparison shown in Figure 6B
(Duncan’s Multiple Range test). Taken together with the increase in intestinal mass (Fig. 3A
), the increases in total intestinal maltase activity from birth to 2 d were calculated to be 3.5- and 13-fold, for the PC and BCP groups, respectively. Lactase activity was highest in the proximal and middle intestine, and across all regions, it decreased significantly from birth to 2 d of age in the MR group (to 35% of values at birth, Fig. 6C
).
The MR group did not differ from the newborn group in intestinal aminopeptidase N activity (Fig. 7A
), whereas feeding PC resulted in a marked increase, and BC feeding resulted in a decrease in this activity. These treatment effects were most pronounced in the distal small intestine. Dipeptidyl peptidase IV activity was not affected by treatment (Fig. 7B
), whereas aminopeptidase A activity (Fig. 7C
) was increased in all three fed groups, relative to values at birth, with the highest values in BCP pigs.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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,15
,16
,26
–30
). The present study has shown that newborn pigs preferentially absorb pIgG (relative to bIgG and other protein macromolecules) and that PC (rather than PM, PP or MR) is required to secure maximal macromolecule absorption during the first 24 h after birth. Colostrum obtained from another species, the cow, also allowed considerable uptake of macromolecules during the first 12 h after birth. Feeding BC mixed with PP proteins (the BCP diet) may thus provide a sufficient level of passive immunization of newborn pigs deprived of sow’s colostrum. Species-specific factors present in colostrum appear to facilitate the endocytosis of large molecules in neonatal pigs.
When the MR (containing few bioactive factors) were fed for 48 h, the increases in intestinal mucosal mass (+120%), villous height and intestinal dimensions were almost identical to the values after colostrum feeding. Nevertheless, elevated intestinal growth has been observed after feeding PC rather than a MR within the first 24 h after birth (10
,11
,15
,16
). In the latter studies, the growth effects may have been only temporary and associated at least in part with the extensive uptake of endocytosed protein into the mucosa during the immediate postnatal period. This hypothesis is supported by the finding that intestinal growth and villous structure at 7 d of age do not depend on whether PC or a MR is fed during the first 24 h after birth (31
). Rapid intestinal growth in newborn pigs is therefore not solely dependent on colostral nutrients or growth factors, although colostrum may have other important effects (immunological, biochemical) on the developing gut.
In the present study, the effects of feeding colostrum on intestinal function were indicated by both the enhanced ability to facilitate absorption of macromolecules and a different enzymatic profile of the intestinal mucosa, compared with MR feeding (less sucrase, more maltase and lactase). The lowered sucrase activity in PC-fed pigs may be related to the lower crypt height (and possibly lower enterocyte turnover) in these pigs, because the enzyme exhibiting this activity (sucrase-isomaltase) is expressed mainly on immature cells at the lower part of the crypt-villus axis (32
). The observed differences in enzyme activities are unlikely to be explained by changes in villous morphology and may thus result from direct diet-dependent effects on the biochemical characteristics of developing enterocytes. A large increase in average maltase activity from birth to 2 d of age, particularly in the BCP group (9-fold increase), indicates that maltase-specific stimulatory components are present in colostrum (both porcine and bovine) and/or in porcine plasma. Either the origin of colostrum (sow or cow) or the presence of PP in the BCP diet may explain why piglets fed the BCP diet differed from those fed the PC diet in sucrase, maltase and aminopeptidase N activities.
The circulating level of IgG in suckling pigs shows a positive relationship with disease resistance in early life (1
). Not only the total level of Ig, however, but also their antigen specificity determines the degree of immunological protection. Hence, the absorption of bIgG from cow’s colostrum by newborn pigs cannot provide notable passive immunity against pig pathogens. Nevertheless, previous studies have shown that newborn pigs survive much better if fed BC rather than MR just after birth (5
). In addition to species- and antigen-specific Ig, colostrum may therefore contain nutrients and bioactive components that have a stimulating effect on maturation, growth and disease resistance in a species-independent manner.
The amount of bIgG fed to the BCP piglets was >3 times that of pIgG, yet the resulting concentrations of the two Ig in plasma were similar. Hence, selectivity exists among the IgG from different species (33
), and absorption does not appear to occur entirely by nonspecific endocytosis of macromolecules. A preference to transport pIgG from the gut lumen to the circulation, independently of diet, could be due to the presence of specific IgG receptors on intestinal enterocytes, similar to the Fc-receptors that exist on the brush border membrane of enterocytes in young rodents (34
,35
). To date, an Fc-receptor has not been identified in the intestine of piglets or calves (36
,37
).
The presence of bioactive components in colostrum may be responsible for the enhanced uptake of macromolecules (pIgG and BSA) from the PC and BCP diets shortly after birth, compared with the PM, PP and MR diets. When macromolecule absorption was tested at 12 h, however, the absorption (using HSA as the macromolecule marker) was much lower in both the BCP and the MR groups, compared with the PC group. Thus, the lack of PC may induce an earlier cessation of macromolecule transport, also known as "intestinal closure." This must be taken into account when Ig are included in diets other than PC for artificially reared piglets. This observation, together with the finding that the diet containing BCP induced changes in brush border enzyme activities that differed from the effect with PC, shows that the intestinal mucosa is very sensitive to dietary stimuli at this critical time. Nevertheless, it appears that feeding BCP is an effective way to ensure that artificially reared newborn pigs receive both immunological protection and a stimulation of intestinal growth and function that are similar to those induced by PC.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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3 Abbreviations used: BC, bovine colostrum; BCP, bovine colostrum with porcine plasma; bIgG, bovine immunoglobulin G; BSA, bovine serum albumin; HSA, human serum albumin; Ig, immunoglobulin; MR, milk-replacer; PC, porcine colostrum; pIgG, porcine immunoglobulin G; PM, porcine milk; PP, porcine plasma.
Manuscript received June 4, 2001. Initial review completed July 23, 2001. Revision accepted September 18, 2001.
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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