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ANIMAL NUTRITION |
Department of Animal Sciences, University of Kentucky, Lexington 40546
| Abstract |
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Key Words: Amino Acids Digestibility Dogs Soybean Meal Whole Soybeans
| Introduction |
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Stachyose and raffinose are two types of oligosaccharides that cannot be cleaved in the intestine due to absence of
-1,6-galactosidase in the small intestinal tract (Zuo et al., 1996
). Yamka et al. (2003)
evaluated soybean meal (SBM) as a protein source in canine foods. When dogs were fed foods containing 3.3 to 5.2% stachyose, they observed a dramatic decrease in small intestinal DM digestibility.
The presence of phytate (myoinositol hexaphosphate) in the diet can limit the availability of P and other minerals (Biehl et al., 1995
; Traylor et al., 2001
). The presence of phytate can decrease nutrient and mineral availability due to the lack of phytase in the gastrointestinal tract of dogs and other monogastric species (Lonnerdal et al., 1999
; Schoenherr et al., 2000
).
More information is needed on the antinutritional factors and their relationship to nutrient availability of soy products in canine foods. Incorporation of whole soybeans into canine foods can lower the expense associated with adding fat and fiber. Thus, the objective of this experiment was to evaluate low-oligosaccharide, low-phytate whole soybeans and SBM as potential feed ingredients for canine foods.
| Materials and Methods |
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Eight mature female mongrel dogs (19.3 ± 0.1 kg) were fitted with ileal cannulas (Walker et al., 1994
) and used to evaluate protein and AA disappearance at the terminal ileum. The dogs were located in the Division of Laboratory Animal Research Facility at the University of Kentucky (Lexington) and were cared for in accordance with Institutional Animal Care and Use Committee-approved protocols. Dogs were housed in an environmentally controlled room at 22°C, with a light:dark cycle of 14:10. The kennels were 1 m x 1.5 m, with a slotted floor sitting 0.2 m above ground. The kennels were adapted to allow for total urine collection. Each kennel was cleaned twice daily, following feeding. Dogs were allowed 25 min of exercise twice daily during adaptation and ileal collection. During total fecal and urine collection, dogs were confined to the cages to ensure that all urine and feces were collected. Water was available ad libitum throughout the experiment.
Feeding and Treatments
The ingredient and chemical composition data for each treatment are presented in Tables 1
and 2
. Each food was kibbled and formulated in accordance with the AAFCO (2000)
nutrient guide for dogs and balanced to meet maintenance requirements. Differences among the four treatments were based on the protein source used in the dry food. The sources of CP were low-oligosaccharide, low-phytate soybean meal (LLM), conventional SBM, low-oligosaccharide, unprocessed low-phytate whole soybeans (LLB) and unprocessed conventional whole soybeans (WSB). Chromic oxide was added to each food at 0.2% of dietary DM to serve as an indigestible marker to determine digestibility. Food was weighed daily and divided into two equal portions and fed at 0700 and 1700 in stainless steel bowls. Each dog was allowed 20 min to consume the food, after which bowls were removed, and orts were weighed and recorded. Throughout the experiment, food samples were collected daily and pooled into plastic collection bags for nutrient content analyses.
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Each experimental period was 14 d long. To avoid meal refusal and gastric upset, dogs were fed a 1:1 mixture of their current food and their respective next experimental food during the first 2 d of the period. Dogs were allowed 6 d for adaptation to each new food.
On the first day of fecal and urine collection (d 7), all feces and urine were removed from the cages and discarded before 0730. Fecal output was collected from this point on for the next 5 d at each mealtime and placed into labeled plastic bags. Fecal scores were determined visually at each collection on a scale from 1 to 5 for volume, stickiness, adhesiveness, and moisture (Table 4
). Samples were frozen as they were collected, and pooled by dog within each period. Urine output was collected via a gutter system at the end of the cage and collected into a plastic container containing 5 mL of 6 M H3PO4. At mealtime, all urine samples were weighed and pooled as they were collected and kept refrigerated until further analyses.
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Analyses
On collection, fecal and ileal samples were stored frozen until they were lyophilized using a Dura-Dry MP Freeze-Drier (FTS Systems, Stone Ridge, NY). Dry matter was determined as the difference in sample weight before and after lyophilization. Fecal samples were then ground to pass a 0.5-mm screen in a Cyclotec 1093 Sample Mill (Tecator, Hoganas, Sweden). Ileal samples were ground using a mortar and pestle. Food samples were ground using a blender (Hamilton Beach/ Proctor-Silex, Inc., Glen Allen, VA). The dried and ground samples were then stored in labeled plastic bags at room temperature until further analysis.
Ileal, fecal, and food samples were dried, ashed, and digested as described by Williams et al. (1962)
. The solutions were allowed to settle and were analyzed the following day using an ATI Unicam 99 atomic absorption spectrophotometer (Cambridge, U.K.) to determine Cr concentrations in the samples. Protein content (N x 6.25) of ileal, fecal, feed, and urine samples were obtained using a Leco CNS2000 (Leco Corp., St. Joseph, MI) N analyzer. Food samples were analyzed for phytate using an ion exchange procedure (Method 986.11; AOAC, 1995
).
Samples of food, ileal, and control samples were prepared for AA analyses according to Methods 988.15 (sulfur and regular) and 994.12 (tryptophan) of the AOAC (1995)
. The resulting solutions were derivatized with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate and AA concentration was determined by reverse phase liquid chromatography using Millipore Waters AccQTag System, as described by Liu et al. (1995)
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Sucrose, raffinose, and stachyose were determined using the following procedure. Ground samples (0.5 to 1 g) were placed into a screw-cap test tube, to which 10 mL of 50:50 (vol/vol) ethanol-water were added. Samples were well mixed, and test tubes were placed into a shaker bath at 40°C for 30 min. The samples were then placed into a sonicator for 10 min. Samples were placed into the shaker bath for an additional 30 min. Following shaking, samples were centrifuged at 750 x g for 15 min, and 1 mL of the supernatant fluid was transferred into a microcentrifuge tube. Samples were then dried using a rotary evaporator (3 to 4 h) and derivatized as described by Knudsen and Li (1990). The resulting solution was analyzed using the Hewlett Packard 5890 Series 2 gas chromatograph with autosampler (Quantum Analytics, Inc., Foster City, CA), as described by Molnár-Perl et al. (1984)
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Calculations and Statistics
Nutrient digestibility was calculated as described by Merchen (1988)
using chromic oxide as an indigestible marker. Marker intakes for digesta flow calculations were corrected for marker recovery in the feces during the 5-d fecal collection. Large intestinal digestibility was calculated as a percentage of that entering the large intestine.
Data were analyzed as a replicated 4 x 4 Latin square using the GLM and REG procedures of SAS (SAS Inst., Inc., Cary, NC). Each dog represented an experimental unit. The model included square, treatment, period within square, and dog within square, and the error was residual error mean square. Preplanned contrasts were used to separate treatment means: LLM vs. SBM, LLB vs. WSB, and SBM and WSB vs. LLM and LLB. Differences were considered significant at P < 0.05.
| Results |
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Nitrogen digestibility and retention data are shown in Table 5
. Although diets were formulated to be isonitrogenous, small differences were observed between treatments resulting in small differences in N intake. Soybean meal resulted in a higher N intake than LLM (P < 0.001), and N intake with LLB was greater than N intake with WSB (P < 0.001). No differences in fecal output or ileal flow were observed for LLM vs. SBM; however, LLB had a higher N fecal output than WSB (P = 0.029). Soybean meal had a higher urine N output than LLM (P = 0.004), and LLB had a greater N urine output than WSB (P < 0.001). Nitrogen retention did not differ among treatments. Small intestinal N digestibility did not differ between LLM- and SBM-containing foods or between LLB and WSB. Large intestinal N digestibility did not differ between LLM- and SBM-containing foods or between LLB and WSB. Total-tract N digestibility did not differ between LLM- and SBM-containing foods or between LLB and WSB.
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| Discussion |
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-galactosidase. The presence of oligosaccharides can also alter digestion by increasing the viscosity of digesta, which can interfere with digestion by decreasing the interaction of digestive enzymes with substrates in the intestine (Smits and Annison, 1996
The WSB and SBM digestibilities observed in the present study are similar those reported by Zuo et al. (1996)
and imply that a low to moderate oligosaccharide content (
3.1%) does not affect small intestinal digestibility of canine foods. Zuo et al. (1996)
investigated the effects of feeding low oligosaccharide SBM and conventional SBM in canine foods. Graded levels (0, 18.6, and 37.1% of DM) of either type of SBM were added to a poultry meal-based diet (8.0 to 20.0% of DM) to determine the effect of oligosaccharides on nutrient digestibility. Stachyose concentrations ranged from 0.1 to 2.7%. Average small intestinal DM and CP digestibility for all soy diets was 61.0 and 68.7%, respectively. The authors concluded that oligosaccharide content of the SBM did not alter the digestibility of the foods. The lower digestibility observed in their study was believed to be the result of utilizing low-quality poultry meal; however, interpretation of these results was confounded by the use of two protein sources.
These studies are not consistent with recent data, which suggest that oligosaccharide content can alter nutrient digestibility. Yamka et al. (2003)
fed graded levels of SBM (15.0 to 46.0% of DM) and found a decrease in small intestinal digestibility. Small intestinal DM digestibility decreased from 80.7 to 33.8%, and small intestinal CP digestibility decreased from 65.1 to 51.1%. The SBM used in their study contained 11.2% stachyose, and the resulting foods contained levels of stachyose ranging from 0.5 to 5.2% of the DM and produced a dramatic decrease in small intestinal DM digestibility (approximately 40 percentage units) when fed to dogs. The levels of stachyose in their foods far exceeded the range of stachyose levels (0.1 to 2.7%) used by Zuo et al. (1996)
and those in the present study. These studies suggest that dogs are affected by oligosaccharides in soy and can tolerate levels up to 3.0% stachyose before a decrease in digestibility is detected, thereby indicating that screening of oligosaccharide content before incorporation into dog foods is essential.
Other antinutritional factors are believed to affect digestibility as well. The presence of phytate in soy products can reduce the digestibility of minerals and other nutrients (Biehl et al., 1995
; Traylor et al., 2001
). This decrease in nutrient availability can occur because of a lack of phytase in the digestive tract of dogs and other monogastric species (Schoenherr et al., 2000
). Reduction of phytate in cereals and oilseeds has been shown to increase mineral availability in monogastrics (Lonnerdal et al., 1999
; Spencer et al., 2000
). Phytase addition to cornSBM-based diets also resulted in increased mineral availability in poultry (Biehl et al., 1995
), as well as increasing the digestibility of methionine, arginine, lysine, proline, histidine, cysteine, lysine, and tryptophan in swine (Mroz et al., 1995
). Although phytase has consistently improved P availability, the interaction of phytate with AA has been more controversial (Adeola and Sands, 2003
). Yamka (2003)
studied the effects of phytate levels on the digestibility of whole soybeans in ilealcannulated dogs. Their study concluded that phytate concentrations
0.15% of the food did not affect the digestibility of canine foods because no differences were observed for small intestinal DM, CP, or AA digestibilities of low-oligosaccharide whole soybeans and LLB foods. The average small intestinal DM and CP digestibilities for their study were 77.2 and 73.4%, respectively. Average AA digestibilities in their study ranged from 66.2 (tryptophan) to 87.4% (methionine). The presence of phytate in this study is not believed to have affected digestibility of the SBM and WSB foods because no differences were observed in small intestinal digestibility for any nutrients evaluated, with the exception of tryptophan, for LLM vs. SBM and LLB vs. WSB.
The effect of processing WSB on canine digestibility has been previously determined. Kendall and Holme (1982)
evaluated the digestibility of various plant products in canine foods. They found that micronized whole soybeans had lower DE and digestible protein when compared with full-fat soy flours and extracted soybean meal. The effects of processing can also be seen in the present study. The two soybean meal (SBM and LLM) diets had higher average digestibilities than the two whole soybean diets (WSB and LLB). When added to foods, unprocessed whole soybeans contain higher levels of antinutritional factors such as tannins, ß-mannans, lectins, saponins, as well as high levels of soluble fiber, which can lower nutrient digestibility (James et al., 1998
; Liener, 2000
). The WSB and LLB used in this study were unprocessed before extrusion. The extrusion process uses high temperatures and pressure, which would inactivate heat labile antinutritional components such as tannins. Unfortunately, extrusion does not inactivate all antinutritional components or decrease the soluble fiber component of the WSB and LLB.Lower digestibilities associated with feeding WSB were demonstrated by the approximately 11.3 percentage unit lower small intestine N digestibility than the two meal diets. This N digestibility data are further supported by the lower amino acid digestibilities in whole soybean diets (LLB and WSB) than in the meal diets (LLM and SBM). Essential AA digestibilities ranged from 5.1 (methionine) to 12.9 percentage units (histidine) lower than for the two meal diets. The LLB diet consistently produced the lowest small intestinal digestibility, raising concerns with AA availability for this diet. Nonessential AA digestibilities were also 5.0 (cysteine) to 11.3 (tyrosine) percentage units lower for the WSB diets.
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| Footnotes |
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2 Correspondence: 814 W. P. Garrigus (phone: 859 257 7515; fax: 859 257 3412; e-mail: dharmon{at}uky.edu).
Received for publication June 10, 2004. Accepted for publication November 17, 2004.
| Literature Cited |
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