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© 2004 The American Society for Nutritional Sciences J. Nutr. 134:2141S-2144S, August 2004

Supplement: WALTHAM International Science Symposium: Nature, Nurture, and the Case for Nutrition

Nutrient Digestibility of Commercial Dog Foods Using Mink as a Model1

Åshild Krogdahl*, Øystein Ahlstrøm{dagger},2 and Anders Skrede{dagger}

* Department of Biochemistry, Physiology and Nutrition, Norwegian School of Veterinary Science, N-0033 Oslo, Norway and {dagger} Department of Basic Sciences and Aquatic Medicine, Agricultural University of Norway, N-1432 Ås, Norway

2 To whom correspondence should be addressed. E-mail: oystein.ahlstrom{at}ihf.nlh.no.

KEY WORDS: • dog food • digestibility • amino acids


EXPANDED ABSTRACT

Nutrient composition and digestibility are of crucial importance for health and well being of animals. Although great attention is paid to nutritional quality in the marketing of dog foods there is usually limited or no independent information on digestibilities. The most highly recognized dog food brands claim to have optimum nutritional quality and high digestibility. In Norway, these brands are usually the most expensive and they offer a set of dog food products with a specific nutrient composition intended for dogs in different life stages. These brands are often sold in pet shops and through veterinaries and they are well recognized by dog owners. Low-priced dog food brands typically have one or two products and they are sold in grocery store chains or sold locally directly from the producer.

The objective of this study was to compare digestibility of six expensive dry dog food brands [high price (HP)3] with six low price dog food brands [low price (LP)] sold in the Norwegian market.


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MATERIAL AND METHODS
 
The six brands of dry dog food included in the HP group were: Eukanuba (large breed puppy), Iams Company, Coevorden, The Netherlands; Proplan (puppy), Nestlé Purina PetCare, St. Louis, MO; Specific (adult), Leo Animal Health, A/S, Uldum, Denmark; Precept (large breed puppy), Texas Farm Products Company, Nacogdoches, TX; Royal Canin (large breed puppy), Royal Canin S.A., Almarques, France; Hill's (large breed puppy), Hill's Pet Nutrition, The Netherlands. Brands in the LP group were: Pedigree (puppy), Masterfoods AB, Malmö, Sweden; Doggy (puppy), Doggy AB, Vårgårda, Sweden; Friskies (puppy), Nestlé Purina PetCare, St. Louis, MO; Troll (puppy) Troll Hundefôr, Trondheim, Norway; Kaisa (adult), Kaisa Hundefôr, Sarpsborg, Norway; Labb (puppy), Felleskjøpet, Oslo, Norway. On average, the price of LP foods was ~50% lower than the price of HP foods.

Three bags from different batches of each food were mixed and fed to four adult (10-mo-old, 2.4–2.6 kg) male mink. Minks were selected as a model due to high accuracy and documented high correlation to digestibility in dogs (1). The mink used were kept for other experiments after termination of this study. Norwegian protocols of experiments involving live animals were followed. The protocols of the digestibility experiment were identical to those used in the experiment by Ahlstrøm and Skrede (1). Digestibility of dry matter, crude protein, amino acids (not tryptophan), crude fat, starch, and total carbohydrates were determined on the basis of analyses of food (one analysis) and freeze-dried feces (average of four separate analyses). In addition, analyses were done on food contents of crude fiber, calcium, phosphorus, and magnesium. Analyses were carried out at AnalyCen AB, Lidköping, Sweden using methods approved by the European Communities and other standardized methods (2–5). Digestibility of gross energy was determined using bomb calorimetric measurements of food and individual samples of feces. The metabolizable energy (ME) content was measured by using 18.8, 39.7, and 17.6 kJ/g digestible crude protein, fat, and carbohydrates, respectively. The general linear model (GLM) procedure of Statistical Analysis System (6) was applied in analysis of variance. The significance of differences in digestibility between foods within each price category were determined by the Ryan-Einot-Gabriel-Welch multiple F-test.


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RESULTS AND DISCUSSION
 
The chemical contents of all the foods corresponded closely to their declarations (not presented here). In brands declaring ME on the package, the ME contents were given to be 14–16 MJ/kg food. The chemical analyses did not reveal any trend between price categories concerning the dietary level of nutrients, except that there was a tendency for less variation among the LP foods (Table 1). The HP foods showed considerable more variation regarding ash, crude protein, crude fat, and carbohydrates than the LP foods did. Food 12 deviated from the other foods by a high-calcium concentration and a high Ca:P ratio. This Ca level of Food 12, (1.9%), corresponded to ~1.3 g Ca/MJ, which is close to the safe upper limit for large breed dogs (7). The Ca level of Food 12 was higher than that declared on the package, indicating a production problem. Except for Food 12, the dietary Ca and P levels were as declared. The magnesium concentrations did not differ between the HP and LP foods and were approximately two to three times higher than the minimum requirement of 26 mg/MJ (8).


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  		TABLE 1 Chemical content in high-price and low-price commercial dry dog foods (%)

The amino acid concentrations in g/kg varied among foods as a result of different amino acid composition of the protein fraction (Table 2).


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  		TABLE 2 Amino acid concentration in high-price and low-price commercial dog foods (g/kg)

Digestibility of main nutrients differed significantly among foods within each price category (Table 3). Crude protein digestibility ranged from 72.7 to 79.7% among HP foods and from 73.9 to 80.4% among LP foods. Corresponding figures for fat digestibility were 76.4–95.8% for HP and 83.9–91.7% for LP foods. Carbohydrate digestibility ranged from 65.0 to 77.1% for HP foods, and from 71.9 to 81.7% for the LP foods. Starch digestibilities were 82.1–97.9% and 90.8–96.3% for HP and LP foods, respectively. Dry matter and energy digestibilities reflected the digestibility values of the main nutrients. The range of dry matter digestibility (68.2–77.0%) found in this study is in accordance with a similar experiment in which the average digestibility of organic matter in 45 extruded dog foods was determined to be 65–88% (8). Comparison of the two food categories, showed no significant differences except for higher carbohydrate digestibility, and as a result of that higher dry matter digestibility among the LP foods than among the HP foods. Generally the standard deviations of the digestibilities were highest among the high-price diets. Diet 5 showed a very low fat digestibility, only 76.4%, which is considerably below the average digestibility of 90% used for calculating ME content in dog food (7). Fat digestibilities measured in our study showed approximately the same variation as in a previous experiment, where fat digestibilities varied between 70 and 90% in extruded dog food (9). Food 1 revealed a particularly low digestibility of starch and carbohydrates indicating that the carbohydrate source had been poor or that processing had not been optimal. Foods like 3 and 4 among the HP foods, and 7, 11, and 12 among the LP foods showed high digestibilities for all main nutrients. The digestibility values of the LP foods are close to or even higher than the digestibility values of ME content in dog food established by National Research Council (1985), which are 80, 90, and 85% for protein, fat, and nitrogen-free extract (NFE), respectively (7). Compared with mink, the model animal in this study, dogs have superior digestive capacity for carbohydrates (1). This implies that if dogs had been used in this study, carbohydrate digestibility values probably would have been 4–10% units higher and would thereby have brought the ME to a level somewhat higher than that shown in Table 3. Carbohydrates accounted for 37.2–53.8% of foods and a 5% increase in the carbohydrate digestibility would have increased the ME content of these foods by 0.35 and 0.47 MJ/kg, respectively.


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  		TABLE 3 Apparent digestibility of nutrients and energy (%), and ME (MJ/kg) in high-price and low-price commercial dry dog foods

As was found for protein, the amino acid digestibilities revealed considerable variation among foods, but were independent of price category (Tables 4, 5). For some of the amino acids the LP foods revealed significantly higher digestibility than in the HP foods (histidine), whereas other amino acids revealed the opposite relationship (cysteine, tyrosine). Generally, foods with a high protein digestibility also showed high amino acid digestibility.


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  		TABLE 4 Apparent digestibility of essential amino acids in high-price and low-price commercial dry dog foods (%)


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  		TABLE 5 Apparent digestibility of nonessential amino acids in high-price and low-price commercial dry dog foods (%)

For all foods, digestible amino acids covered requirements for growing dogs established by the National Research Council. For arginine, phenylalanine + tyrosine, histidine, isoleucine, leucine, and valine, the 10 foods intended for growing dogs exceeded the requirements by 100–300%. For methionine + cysteine, lysine, and threonine, the diets exceeded requirements by 40–100%. The two diets produced for adult dogs also met the requirement of essential amino acids for growing dogs.

Conclusions

Digestibility of main nutrients varies significantly among commercial dry dog foods. This study demonstrated that there is no difference in digestibility of nutrients between high-price and low-price dog foods offered in the Norwegian market.


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FOOTNOTES
 
1 Presented as part of the WALTHAM International Science Symposium: Nature, Nurture, and the Case for Nutrition held in Bangkok, Thailand, October 28–31, 2003. This symposium and the publication of the symposium proceedings were sponsored by the WALTHAM Centre for Pet Nutrition, a division of Mars, Inc. Symposium proceedings were published as a supplement to The Journal of Nutrition. Guest editors for this supplement were D'Ann Finley, James G. Morris, and Quinton R. Rogers, University of California, Davis. Back

3 Abbreviations used: HP, high price; LP, low price; ME, metabolizable energy; NFE, nitrogen-free extract. Back


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LITERATURE CITED
 
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O. Ahlstrom, A. Krogdahl, S. G. Vhile, and A. Skrede
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J. Nutr., August 1, 2004; 134(8): 2145S - 2147S.
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