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Institute of Food, Nutrition and Human Health, Massey University, Palmerston North, New Zealand
2To whom correspondence should be addressed. E-mail: W.Hendriks{at}massey.ac.nz.
KEY WORDS: • dogs • amino acid digestibility • fecal • ileal
EXPANDED ABSTRACT
Ingredients used to manufacture pet foods vary in their ability to deliver nutrients to the animal. The digestible content of nutrients in the final pet food is important to ensure that an animal can absorb sufficient nutrients from the diet to meet its requirements. To determine the digestible content of a nutrient, an estimate of the digestibility of that nutrient needs to be obtained. Traditionally with cats and dogs, digestibility measurements are made over the entire gastrointestinal tract, something that may not be accurate because of microbial fermentation in the large intestine. In other animals such as rats, chickens, pigs and humans it has been shown that there is significant metabolism of dietary nutrients in the large intestine (1–3) and subsequently the apparent fecal digestibility method has been labeled as an inaccurate method for the measurement especially of protein and amino acid digestibility. In cats and dogs, however, it can be argued that large intestinal metabolism may not be significant, given that these two carnivores have a relatively small and "underdeveloped" large intestine with a relatively low capacity and a low coefficient of differentiation (4,5).
The aim of the present study was to compare protein and amino acid digestibility at the distal ileum and over the entire digestive tract of adult dogs.
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MATERIALS AND METHODS |
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 TOP MATERIALS AND METHODS RESULTSDISCUSSIONLITERATURE CITED |
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Five healthy adult dogs (3 males, 2 females) of mixed breed with an initial body weight range of 15–25 kg (mean ± SEM, 20 ± 2.4 kg), scheduled for destruction, were housed individually in outdoor concrete kennels at Jenners Mead Farm (Fielding, New Zealand). The dogs had received a broad-spectrum anthelmintic containing pyrantel embonate, oxantel embonate and praziquantel (Canex Multi Spectrum All Wormer; Pfizer Animal Health, Auckland, New Zealand) 1 wk before the study began. The dogs were fed a commercial dry dog food containing (g/100 g): crude protein, 27; fat, 13; ash, 5; calcium, 0.5; phosphorus, 0.4; and 3.6 kcal ME/g to energy requirements [132 kcal/kg0.75 body weight (7)]. The diets were ground over a 2-mm screen and chromic oxide (2.5 g/kg diet) was homogenously mixed through the diet. Each day’s total food allowance was given in 10 equal portions, beginning hourly at 0800. The diets were fed for 10 d and water was available at all times. The dogs were exercised for 1 h/d, with care being taken to prevent the dogs from consuming other material during this time. A fecal sample from each dog was collected on d 9 of the study. On d 10, 4.5 h after the start of the hourly feeding, the dogs were killed with an intravenous injection of sodium pentobarbitone (300 mg/mL; Chemstock Animal Health, Christchurch, New Zealand), their body cavity opened and 20 cm of ileum anterior to the ileocaecal junction was immediately dissected out. The outside of the dissected ileum was washed with distilled deionized water to remove any blood and hair and then carefully blotted using an absorbent paper towel. The ileal content was gently flushed into a plastic bag using a syringe containing distilled deionized water. The entire procedure from euthanasia of the dogs to recovery of the ileal digesta took between 1 and 2 min. The samples were frozen (-20°C) immediately after collection, freeze-dried and stored (-20°C) until chemical analyses. Ileal digesta, feces and diet samples were analyzed for dry matter, organic matter, chromium, nitrogen and amino acids in duplicate, as described by Hendriks et al. (8).
Digestibility values were calculated using the chromium concentration per unit dry matter in excreta and diet. Students’ t-test was used to determine differences in digestibility values for nutrients between the distal ileum and entire digestive tract.
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RESULTS |
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TOPMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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DISCUSSION |
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TOPMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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The most accurate site for the measurement of the amount of a nutrient or group of nutrients absorbed from the diet depends on the nutrient or group of nutrients under investigation. Because measurement of digestibility aims to determine the absorption of dietary nutrients by the animal, the ability of the colon to absorb nutrients will theoretically determine the most accurate site for measurement of digestibility. The colon of the dog has been shown to have the capability to absorb amino acids in vitro (11). However, in practice, the contribution of the large intestine to overall amino acid absorption is believed to be limited in dogs (12). Therefore, any metabolism of dietary nutrients and de novo synthesis of nutrients by the microflora of the large intestine will only confound the estimation of the amino acids absorbed by the animal. The present study shows that there is a significant alteration of the digestible amino acid pattern by the large intestine of dogs and that there is a net absorption of N-containing compounds in the large intestine and as a result crude protein digestibility (N x 6.25) is overestimated in dogs fed a dry dog food. Meyer et al. (12), Muir et al. (9) and Murray et al. (10) all found lower crude protein digestibility values when measured at the distal ileum. A better estimate of overall protein digestibility can be obtained by measurement of amino acid nitrogen digestibility, given that there was no significant difference in the estimates between the two sites in the present study.
The fecal digestibility assay is relatively simple to conduct and a detailed procedure has been published by AAFCO (13) involving either total collection or the use of an indigestible marker. Obtaining a digesta sample from the distal ileum is more difficult. Cannulation, anastomosis and sampling under anesthesia are the most commonly used methods to obtain ileal digesta samples in monogastric animals. No research has been conducted to evaluate the various techniques to obtain ileal digesta samples in dogs. In growing pigs, however, the same technique as used in the present study has been found to produce similar estimates with similar variances compared to those obtained by the simple T-cannulation technique (14,15).
Although the large intestine of the dog is relatively short, dietary or endogenous nutrients entering the large intestine are metabolized by the microflora. The apparent fecal digestibility method is not an accurate method for the measurement of the absorption of crude protein and certain amino acids from canine diets.
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FOOTNOTES |
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LITERATURE CITED |
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TOPMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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1. Sauer, W. C. & Ozimek, L. (1986) Digestibility of amino acids in swine: results and their practical application. A review. Livest. Prod. Sci. 15:367-388.
2. Butts, C. A., Darragh, A. J. & Moughan, P. J. (1991) The protein nutrition of simple-stomached mammals, birds and fishes. Proc. Nutr. Soc. NZ 16:60-81.
3. Rowan, A. M., Moughan, P. J. & Wilson, M. N. (1994) Comparison of the ileal and faecal digestibility of dietary amino acids in adult humans and evaluation of the pig as a model animal for digestion studies in man. Br. J. Nutr. 71:29-42.[Medline]
4. Chivers, D. J. & Hladik, C. M. (1980) Morphology of the gastrointestinal tract in primates: comparisons with other mammals in relation to diet. J. Morph. 166:337-386.
5. Argenzio, R. A. (1993) General functions of the gastrointestinal tract and their control and integration. Swenson, M. J. Reece, W. O. eds. Duke’s Physiology of Domestic Animals 1993:325-375 Comstock Publishing Associates Ithaca, NY .
6. Anonymous (1992) Code of Ethical Conduct for the Use of Live Animals for Teaching and Research rev. ed. 1992 Massey University Palmerston North, New Zealand .
7. NRC (1985) Nutrient Requirements of Dogs 1985 National Academy Press Washington, DC .
8. Hendriks, W. H., Moughan, P. J. & Tarttelin, M. F. (1996) Gut endogenous nitrogen and amino acid excretions in adult domestic cats fed a protein-free or an enzymatically hydrolyzed casein-based diet. J. Nutr. 126:955-962.
9. Muir, H. E., Murray, S. M., Fahey, G. C., Jr, Merchen, N. R. & Reinhart, G. A. (1996) Nutrient digestion by ileal cannulated dogs as affected by dietary fibers with various fermentation characteristics. J. Anim. Sci. 74:1641-1648.[Abstract]
10. Murray, S. M., Patil, A. R., Fahey, G. C., Jr, Merchen, N. R. & Hughes, D. M. (1998) Raw and rendered animal by-products as ingredients in dog diets. J. Nutr. 128:2812S-2815S.
11. Robinson, J.W.L., Luisier, A. L. & Mirkovitch, V. (1973) Transport of amino-acids and sugars by the dog colonic mucosa. Pfluegers Arch 345:317-326.[Medline]
12. Meyer, H., Schünnemann, C., Elbers, H. & Junker, S. (1987) Precaecal and post ileal protein digestion and intestinal urea conversion in dogs. Edney, A.T.B. eds. Nutrition, Malnutrition and Dietetics in the Dog and Cat, Proceedings of an international symposium, Hannover, Germany 1987:27-30 Br. Vet. Assoc. London, UK .
13. AAFCO (2000) Official Publication of the Association of American Feed Control Officials 2000 Atlanta, GA .
14. Moughan, P. J. & Smith, W. C. (1987) A note on the effect of cannulation of the terminal ileum of the growing pig on the apparent ileal digestibility of amino acids in ground barley. Anim. Prod. 44:319-321.
15. Donkoh, A., Moughan, P. J. & Smith, W. C. (1994) Comparison of the slaughter method and simple T-piece cannulation of the terminal ileum for determining ileal amino acid digestibility in meat and bone meal for the growing pig. Anim. Feed Sci. Technol. 49:43-56.
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