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Nutrient Metabolism

Pullulans and -Cyclodextrin Affect Apparent Digestibility and Metabolism in Healthy Adult Ileal Cannulated Dogs^1,2

Department of Animal Sciences, University of Illinois, Urbana, IL 61801 and ^* Ross Products Division, Abbott Laboratories, Columbus, OH 43215

³To whom correspondence should be addressed. E-mail: gcfahey{at}uiuc.edu.

	ABSTRACT

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Pullulan and -cyclodextrin are incompletely digestible, glucose-based, nonstructural carbohydrates synthesized by microorganisms. To determine their effect when incorporated into a complete liquid diet on ileal and total tract nutrient digestibility, ileal cannulated dogs (n = 8) were used in a repeated 4 x 4 Latin-square design. Twice daily, diets were offered containing 30% (DMB) maltodextrin, high-molecular-weight (MW) pullulan (MW 100,000), low-MW pullulan (MW 6300), or -cyclodextrin. Fecal and ileal samples were collected for the last 4 d of each 10-d period. Dogs consuming high-MW pullulan had lower (P < 0.05) dry matter, organic matter, crude protein, fat, carbohydrate ileal and total tract digestibilities, and fecal DM, and higher (P < 0.05) fecal output and fecal scores (indicating looser stools). To evaluate glycemic and insulinemic responses to pullulans, food-deprived dogs consumed 25 g maltodextrin, high-MW pullulan, or low-MW pullulan in a repeated 3 x 3 Latin-square design. Glucose and insulin responses were determined for 180 min. Consumption of 25 g -, ß-, and -cyclodextrin resulted in regurgitation within 60 min. High-MW pullulan reduced (P < 0.05) blood glucose concentration at 15, 30, 45, and 60 min. Compared with maltodextrin, low-MW pullulan and -cyclodextrin did not alter nutrient digestibilities or fecal characteristics to any extent, and low MW pullulan did not affect glycemic response. Although high MW pullulan decreased glycemic response, consumption of large amounts negatively affected nutrient digestibility and fecal characteristics.

KEY WORDS: • canine • digestibility • -cyclodextrin • glycemic index • pullulan

The control of blood glucose in humans with noninsulin-dependent (Type 2) diabetes mellitus is of paramount importance for the long-term management of this disease (1,2). Concomitant use of diet as adjunctive therapy for the management of blood glucose may further enhance the quality of life and reduce the risk of hypoglycemia and weight gain. The formulation of novel foods that attenuate the postprandial glycemic excursion should enhance the use of nutrition as adjunctive therapy for humans suffering from this condition.

As part of a healthy nutritional regimen, it is recommended that diabetic individuals consume diets low in fat and high in complex carbohydrates and dietary fiber (1). Diets that contain complex carbohydrates attenuate the glycemic response due to a slower rate of carbohydrate digestion. Dietary complex carbohydrates that provide energy yet do not exacerbate hyper- or hypoglycemic conditions are of particular importance to diabetic patients (1). Additionally, incorporation of soluble complex carbohydrates in liquid diets serves a critical role for diabetic individuals who are unable to consume adequate solid foods. Several novel soluble glucose-based polymers have been developed as potential ingredients in nutritional beverages for diabetics.

Experimentation with pullulans and cyclodextrins supports their use for humans and animals with diabetes (3,4). Pullulan is a linear homopolysaccharide of glucose that is an -1,6 linked polymer of maltotriose subunits (5). Cyclodextrins are cyclic oligosaccharides composed of -1,4-glycosidic-linked glucose residues. There are 3 major types of cyclodextrins categorized by number of glucose molecules: -, ß-, and -cyclodextrins are composed of 6, 7, and 8 glucose units, respectively (6). Pullulans and cyclodextrins are incompletely digestible, glucose-based, nonstructural carbohydrates (5,6). Although a fraction of these polymers is digested and absorbed in the stomach and small intestine, the remainder is resistant to digestion and passes into the large intestine. Previous research has demonstrated that high-molecular-weight pullulan decreases the glycemic response in healthy humans (3). No published research has been conducted comparing the glycemic response of cyclodextrins, even though they are considered incompletely digestible nonstructural carbohydrates.

To incorporate novel glucose polymers into nutritional beverages, the digestibility and glycemic response of these carbohydrates must be determined. The objectives of this research were as follows: 1) to determine the effects of novel glucose polymers as components of a complete liquid diet on ileal and total tract apparent digestibilities of dry matter (DM),⁴ organic matter (OM), fat, crude protein (CP), and carbohydrate, and 2) to evaluate the glycemic and insulinemic response to low- and high-molecular-weight pullulans in healthy adult ileal cannulated dogs.

	MATERIALS AND METHODS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Expt. 1

    Animals. Purpose-bred female dogs (n = 8; Butler Farms USA) with hound bloodlines, an initial body weight of 22.2 kg (range, 18.8–27.8 kg), and 2.0 y old (range, 0.9–5.7 y) were surgically prepared with an ileal cannula according to Walker et al. (7). Surgical and animal care procedures were approved by the University of Illinois Animal Care and Use Committee before initiation of the experiment. After surgery, dogs were closely monitored and allowed a 2-wk recovery period before the experiment. Dogs were housed individually in kennels in a temperature-controlled room (21°C) at the animal care facility in the Edward R. Madigan Laboratory, University of Illinois. A 16-h light:8-h dark schedule was used.

    Dietary treatments. Enteral formulas (n = 4) were evaluated in the study (Table 1). Ingredients were identical except for the type of carbohydrate added. Carbohydrates used were high-molecular-weight pullulan (MW = 100,000; Hayashibara), low-molecular-weight pullulan (MW = 6300; Hayashibara), -cyclodextrin (Wacker Biochem), and maltodextrin (control: Polycose, Ross Products Division, Abbott Laboratories). High-molecular-weight pullulan, -cyclodextrin, and maltodextrin were dry powders; low-molecular-weight pullulan was a syrup. To ensure that the same amount of carbohydrate was added to diets on a DM basis, 63.0 g of the dry carbohydrates was used, whereas 86.5 g of the low-molecular-weight pullulan syrup was added at each feeding. Vitamins and minerals were added to meet the AAFCO (8) recommendations for dogs at maintenance. Diets contained 50% carbohydrate (50% of this was the test carbohydrate, 25% was maltodextrin, and 25% was sucrose), 24% protein, 15% fat, and 5% ash. By using low concentrations of digestible protein and fat sources and adding high concentrations of carbohydrate, it is possible to investigate whether consumption of high concentrations of the test carbohydrates would have negative effects on both digestibility and fecal characteristics. Because this study was specifically examining digestibility of the test carbohydrates and their effects on stool quality, the liquid diet composition was different from the composition of a typical beverage. Diets were mixed immediately before feeding. Dogs were provided 1 L (1000 g) of diet twice daily (0800 and 2000 h). Diets were formulated to supply 8370 kJ metabolizable energy/d. Chromic oxide was used as a digestion marker. Dogs were dosed with 0.5 g Cr₂O₃ at each feeding via gelatin capsule for a total of 1.0 g marker/d. Water was consumed ad libitum.

View this table: [in this window] [in a new window]   TABLE 1 Ingredient composition of dietary treatments for dogs consuming maltodextrin (control), high-molecular-weight pullulan, low-molecular-weight pullulan, or -cyclodextrin in an enteral formula (Expt. 1)

Total feces excreted during the collection phase of each period were removed from the floor of the pen, weighed, composited, and frozen at –20°C. During the 4-d collection phase, all fecal samples were scored (by one individual) according to the following system: 1 = hard, dry pellets; small hard mass; 2 = hard, formed, dry stool; remains firm and soft; 3 = soft, formed, and moist stool; 4 = soft, unformed stool; assumes shape of container; 5 = watery; liquid that can be poured.

    Sample handling. Ileal samples were frozen at –20°C in their individual bags. At the end of the experiment, all ileal effluent samples were combined for each dog for each period, and then refrozen at –20°C. Before analysis, dietary treatments and ileal effluent were lyophilized in a Dura-Dry MP microprocessor-controlled freeze-drier (FTS Systems). Feces were dried at 55°C in a forced-air oven. After drying, diets, fecal samples, and ileal samples were ground through a 2-mm screen in a Wiley mill (model 4, Thomas Scientific).

    Chemical analyses. Diets, feces, and ileal samples were analyzed for DM, OM, and ash using AOAC (9) methods. CP concentrations were calculated using Leco® nitrogen values (N x 6.25) for all samples using AOAC (9) methods. Total lipid content was determined by acid hydrolysis followed by ether extraction according to the American Association of Cereal Chemists (10) and Budde (11). Fecal samples were prepared for diaminopimelic acid (DAPA) analysis by acid hydrolysis (12), and DAPA concentrations were determined using ion-exchange chromatography (13) on a GoldDV711 chromatograph (Beckman Instruments). To prevent coelution of DAPA with methionine, Beckman System 6300 High Performance Amino Acid Analysis Buffer Na-F^TM (Beckman Instruments) was diluted at a rate of 1.6:1 with water, resulting in an increase in total program time of 7 min. This led to an improved selectivity of the peaks, with methionine eluting at 34 min, DAPA at 34.7 min, and a total program time of 80 min. Gross energy content of dietary treatments was determined by use of a bomb calorimeter (Parr Instrument; Parr Instrument Manuals). Chromium in feces and ileal samples was analyzed according to Williams et al. (14) using an atomic absorption spectrophotometer (Model 2380, Perkin-Elmer).

    Calculations. The carbohydrate content of all samples was calculated as the difference between OM and the sum of CP and lipid concentrations. DM (g/d) recovered as ileal effluent was calculated by dividing the Cr intake (mg/d) by ileal Cr concentrations (mg Cr/g ileal effluent). Ileal nutrient flows were calculated by multiplying DM flow by the concentrations of the nutrient in the ileal DM. Ileal nutrient digestibilities were calculated as nutrient intake (g/d) minus the ileal nutrient flow (output, g/d), divided by nutrient intake (g/d). The same calculations were performed with fecal samples to determine total tract nutrient digestibilities. Bacterial N concentrations as a percentage of total N in fecal samples were determined by dividing the standard value of N:DAPA of bacterial rich samples isolated from canine feces of 18 [(as determined in (15)] by the N:DAPA ratio found in fecal samples.

Expt. 2

    Animals. Purpose-bred female dogs (n = 6; Butler Farms USA) with hound bloodlines, an initial body weight of 28.9 kg (range, 27.2–30.9 kg), 4.2 y old (range, 2.8–7.7 y), and possessing an ileal cannula were used.

    Dietary treatments. Three carbohydrates were evaluated in this experiment: 1) maltodextrin (Control; Polycose, Ross Products Division, Abbott Laboratories), 2) high-molecular-weight pullulan (mean-molecular-weight of 100,000; Hayashibara), and 3) low-molecular-weight pullulan (mean molecular weight of 6300; Hayashibara). Dogs consumed 25 g of carbohydrate in 240 mL distilled-deionized water for the meal tolerance test. Dose amount was measured using a disposable 60-mL syringe (without needle) and offered to dogs over a 10-min period.

    Experimental design. A repeated 3 x 3 Latin-square design was used in which dogs were subjected to 3 separate 3-h meal tolerance tests. Tolerance tests were spaced 7 d apart. After 15 h of food deprivation, dogs consumed their allotted treatment.

All dogs were fed the same commercial diet (Iams Weight Control® Iams). The main ingredients of the diet were cornmeal, chicken, ground whole-grain sorghum, chicken by-product meal, ground whole-grain barley, and fish meal. Water was freely available. At 1700 h on the evening before each meal tolerance test, any remaining food was removed, and dogs were food deprived for 15 h, during which they consumed only water.

The morning of the meal tolerance test, a blood sample was obtained from food-deprived dogs. Dogs then were dosed with the appropriate carbohydrate solution, and additional blood samples were taken at 15, 30, 45, 60, 90, 120, 150, and 180 min postprandially. Approximately 5 mL of blood was collected via jugular or radial venipuncture and placed in vacutainer serum separator tubes for analyses. An aliquot of blood was taken immediately for glucose analysis. Tubes were kept at room temperature for transportation back to the laboratory. Tubes were centrifuged at 1240 x g at room temperature for 10 min, and serum supernatant was stored at 4°C for analysis.

    Chemical analyses. Immediately after collection, blood samples were assayed for glucose by the glucose oxidase method utilizing a Precision-G Blood Glucose Testing System (Medisense). The precision of this testing system for the range of values obtained was 3.4–3.7% (CV), as reported by the manufacturer.

Serum insulin was analyzed by RIA using the Immunolite analyzer (chemiluminescence; Diagnostics Products) by a contract laboratory (Antech Diagnostics).

    Statistical analysis. Data for Expts. 1 and 2 were analyzed by the Mixed models procedure of SAS (SAS Institute). Expt. 1 was a replicated 4 x 4 Latin-square design. Expt. 2 was a repeated 3 x 3 Latin-square design. The statistical model for both experiments included the fixed effect of treatment and the random effects of animal and period. Treatment least-squares means were compared using Tukey’s method. A probability of P < 0.05 was accepted as significant although, for Expt. 2, differences with P < 0.10 were accepted as trends and results discussed accordingly.

	RESULTS

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Expt. 1

    Animals and dietary treatments. One dog was removed from the study due to low food intake unrelated to treatment. Dietary treatments contained similar concentrations of all components measured (Table 2).

View this table: [in this window] [in a new window]   TABLE 2 Chemical composition of dietary treatments for dogs consuming maltodextrin (control), high-molecular-weight pullulan, low-molecular-weight pullulan, or -cyclodextrin in an enteral formula (Expt. 1)

View this table: [in this window] [in a new window]   TABLE 3 Nutrient intakes, digestibilities, and proportion of fecal N of bacterial origin in dogs consuming maltodextrin (control), high-molecular-weight pullulan, low-molecular-weight pullulan, or -cyclodextrin in an enteral formula (Expt. 1)1

Total tract DM, OM, and carbohydrate digestibilities were 15% lower (P < 0.05) for dogs consuming the high-molecular-weight pullulan–containing diet compared with all other dietary treatments (Table 3). Total tract CP digestibilities were 12 percentage units lower (P < 0.05) for dogs fed the high-molecular-weight pullulan diet than for those fed other dietary treatments. Dogs had lower (P < 0.05) total tract CP digestibilities when fed -cyclodextrin–containing diets compared with the low-molecular-weight pullulan and maltodextrin diets. Total tract digestibility of fat was lower (P < 0.05) in dogs consuming high-molecular-weight pullulan– and -cyclodextrin–containing diets than in those fed the maltodextrin-containing diets.

    Fecal characteristics. Fecal output (g/d), expressed on an as-is and a DM basis, was much higher (P < 0.05) for dogs consuming the high-molecular-weight pullulan diet than in the other 3 groups (Table 4). When fecal output was expressed as as-is output/g DM consumed, the output of dogs consuming the high-molecular-weight pullulan diet was 600% higher than that of other groups (P < 0.05). Fecal DM was lowest (P < 0.05) for dogs fed the high-molecular-weight pullulan-containing diet than for dogs in the other groups. Fecal scores were higher (P < 0.05) for dogs fed the high-molecular-weight pullulan diet than for all other dogs, indicating that they had very loose stools. Dogs fed the maltodextrin diet had a lower (P < 0.05) fecal score than did those fed the -cyclodextrin diet.

View this table: [in this window] [in a new window]   TABLE 4 Fecal characteristics of dogs consuming maltodextrin (control), high-molecular-weight pullulan, low-molecular-weight pullulan, or -cyclodextrin in an enteral formula (Expt. 1)1

    Animals. One dog was removed from the study due to treatment refusal.

    Incremental blood glucose and serum insulin concentrations. At 15, 30, 45, and 60 min postprandial, blood glucose of dogs consuming high-molecular-weight pullulan was lower (P < 0.05) than that of dogs consuming maltodextrin (Fig. 1). At 15 min postprandial, blood glucose concentrations were lower (P < 0.05) for dogs consuming high-molecular-weight pullulan than those consuming low-molecular-weight pullulan.

View larger version (24K): [in this window] [in a new window]   FIGURE 1 Incremental change from baseline in capillary blood glucose response for dogs consuming 25 g of carbohydrate from maltodextrin (control), low-molecular-weight pullulan, or high-molecular-weight pullulan (Expt. 2). Values are least-squares means ± SEM, n = 5. Least-squares means at a time without a common letter differ, P < 0.05.

View larger version (28K): [in this window] [in a new window]   FIGURE 2 Incremental change from baseline in serum insulin response for dogs consuming 25 g of carbohydrate from maltodextrin (control), low-molecular-weight pullulan, or high-molecular-weight pullulan (Expt. 2). Values are least-squares means ± SEM, n = 5.

	DISCUSSION

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Ileal nutrient digestibilities by dogs not consuming the high-molecular-weight pullulan diet were similar to ileal digestibilities by dogs fed other enteral formulas [e.g., mean ileal DM digestibility of 88% (16)]. Low ileal nutrient digestibilities by dogs consuming high-molecular-weight pullulan may be due to differences in digesta flow rate. Although the mean flow rate for dogs consuming the low-molecular-weight pullulan–, -cyclodextrin–, and maltodextrin-containing diets was 43.7 g DM/d, the mean flow rate for dogs consuming the high-molecular-weight pullulan diet was 117.7 g DM/d. This high flow rate would decrease retention time in the small intestine, impeding nutrient absorption, and is most likely due to an osmotic effect of high-molecular-weight pullulan. When incompletely digestible nonstructural carbohydrates are not absorbed in the small intestine, they exert an osmotic effect in the intestinal lumen (17). The osmotic effect increases the water flow rate, and may induce abdominal pain and, eventually, diarrhea if the capacity of the colon to absorb water and electrolytes is exceeded. These processes lead to an elevated water load entering the colon when osmotically active, incompletely digestible nonstructural carbohydrates are ingested (17).

Differences noted in total tract digestibility perhaps were due to an increased digesta flow rate as mentioned above. Total tract nutrient digestibilities by dogs not consuming the high-molecular-weight pullulan diet were similar to those for dogs fed other enteral formulas [e.g., total tract DM digestibility of 93% (16)].

Fecal characteristics of dogs consuming high-molecular-weight pullulan were not desirable and reflected the increased digesta flow rate experienced by the dogs consuming this diet. Fecal DM output by dogs consuming maltodextrin, low-molecular-weight pullulan, and -cyclodextrin diets were slightly lower than mean fecal DM output values for dogs fed dry extruded diets [e.g., 45 g/d; (16)]. The slight decrease in fecal output is due to the high digestibility of the enteral diets.

Digestibility and fecal characteristics of dogs consuming high-molecular-weight pullulan reflect general attributes of incompletely digestible nonstructural carbohydrates. A portion of high-molecular-weight pullulan is available for enzymatic hydrolysis in the small intestine, and another portion is available for fermentation in the colon (5). Certain incompletely digestible nonstructural carbohydrates have a high rate of fermentation in the colon, leading to greater quantities of SCFA and gases [carbon dioxide, hydrogen, and methane (18)]. Abdominal discomfort, flatus, and diarrhea may result from this process. In addition, rapid fermentation of these carbohydrates may yield lactate and SCFA at a faster rate than can be absorbed, temporarily promoting diarrhea (18).

Reducing the molecular weight of pullulan appears to make it more available for rapid enzymatic digestion in the small intestine. Okada et al. (19) investigated the digestion and fermentation of pullulans with different molecular weights (5000–200,000) in vitro. During simulated hydrolysis, the amount of glucose produced increased as pullulan molecular weight decreased, indicating that small intestinal enzymes more readily hydrolyze lower-molecular-weight pullulans. When pullulan molecular weights were >65,000, the amount of glucose formed from small intestinal enzymatic digestion was constant at 1.5%, indicating that high-molecular-weight pullulans are more resistant to small intestinal enzymatic hydrolysis. Reducing the molecular weight of the pullulan molecule increases its availability for digestion and absorption in the small intestine.

This study demonstrated that although high-molecular-weight pullulan decreased the postprandial glucose response, low-molecular-weight pullulan caused a postprandial glycemic response similar to that of maltodextrin. High-molecular-weight pullulan decreased (P < 0.05) the blood glucose response at 15, 30, 45, 60, and 90 min postprandial compared with maltodextrin fed to humans (3). At 120, 150, and 180 min postprandial, dogs consuming both pullulans had higher blood glucose concentrations than those consuming maltodextrin. These results are similar to other pullulan glycemic index research in which plasma glucose was maintained above baseline at 150 and 180 min postprandial when human subjects consumed high-molecular-weight pullulan [molecular weight of 100,000 (3)]. An elevated plasma glucose concentration at 3 h postprandial indicates that both pullulans are absorbed more slowly than maltodextrin.

The postprandial serum insulin response was similar to the glycemic response; however, serum insulin data were much more variable than plasma glucose data. Samples taken from the peripheral blood represent the net effect of a number of postabsorptive processes. The liver extracts a substantial portion of the total insulin secreted from the pancreas; therefore, insulin concentration in the peripheral blood is much lower than concentrations observed in the portal blood (20). Variation in insulin response is attributable to substantial (40–80% of total insulin) and variable hepatic insulin extraction (21).

The regurgitation response noted when dogs consumed -, ß-, and -cyclodextrin has never been documented previously. Previous research with a toxicological emphasis involved feeding dogs higher amounts than what was offered in the glycemic study. Bär and Lina (22) fed beagle dogs 10 g -cyclodextrin/kg BW (20% of the diet) with no adverse side effects except transient diarrhea. Bellringer et al. (23) fed beagle dogs 50,000 mg/kg diet ß-cyclodextrin [1900 mg/(kg BW · d)] and reported a higher incidence of diarrhea. Till and Bär (24) reported that beagle dogs consumed 7.7 g/kg BW -cyclodextrin without adverse effects. Koutsou et al. (25) examined the gastrointestinal tolerance of -cyclodextrin in healthy humans. After a single dose of 8 g maltodextrin or -cyclodextrin in 100 g, subjects reported flatulence after -cyclodextrin consumption, indicating carbohydrate malabsorption. Raben et al. (4) studied the glycemic response of starch enriched with 2% ß-cyclodextrin in healthy adult humans, and no adverse effects were reported. In Expt. 1, dogs consumed 63.0 g of -cyclodextrin in an enteral diet without regurgitation or diarrhea resulting. In each of these studies, cyclodextrins were included in a diet matrix; perhaps this is key for cyclodextrin tolerance by dogs.

Regurgitation could be caused by consumption of a bolus of cyclodextrin in water only, which may affect palatability or molarity. The cyclodextrin solution may have been unpalatable to dogs. Cyclodextrins are not tasteless, but they are commonly used in complexes to enhance or suppress flavors (26). Calculated molarity, a measure of solution concentration expressed in moles of solute per liter of solution, was higher for the cyclodextrin solutions compared with either pullulan. Molarity of the cyclodextrin solutions was 0.11, 0.09, and 0.08 mol/L for -, ß-, and -cyclodextrin, respectively, whereas the respective molarity for low-molecular-weight and high-molecular-weight pullulans was 0.001 and 0.02 mol/L. The higher concentration of cyclodextrins in the solution may have caused regurgitation by affecting electrolyte balance or water binding. The hydrophobic interior of the cyclodextrins allows these carbohydrates to form inclusion bodies with hydrophobic molecules, thus changing their physicochemical properties (27).

In conclusion, although the carbohydrates fed to dogs in this study contained only glucose, differences in digestibility, fecal characteristics, and glycemic index were noted. Maltodextrin is a linear carbohydrate composed of -1,4 bonds that are rapidly hydrolyzed and absorbed. Although pullulan is linear as well, it contains -1,6 bonds resistant to mammalian small intestinal enzymes. In addition, it is clear that pullulan chain length affects digestibility, with higher-molecular-weight pullulans being less digestible. Although -cyclodextrin is composed entirely of -1,4 bonds, the cyclical structure of this novel glucose polymer results in steric hindrance of amylases. These novel carbohydrates, although composed entirely of glucose, result in very different responses when consumed due to their unique bonds and stereochemistry.

	FOOTNOTES

 
¹ Presented at Experimental Biology 05, April 2005, San Diego, CA [Spears, J. K., Karr-Lilienthal, L. K. & Fahey, G. C., Jr. (2005) Apparent digestibility of pullulans and -cyclodextrin when incorporated into an enteral formula, and glycemic and insulinemic responses to pullulans in healthy adult ileal cannulated dogs. FASEB J. 19: A1349 (abs.)].

² Funded in part by Ross Products Division, Abbott Laboratories, Columbus, OH 43215.

⁴ Abbreviations used: CP, crude protein; DAPA, diaminopimelic acid; DM, dry matter; MW, molecular weight; OM, organic matter.

Manuscript received 9 March 2005. Initial review completed 15 April 2005. Revision accepted 9 May 2005.

	LITERATURE CITED

TOP ABSTRACT MATERIALS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 

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