Diets

Eight commercially available diets were selected that varied in diet type (canned or kibble) and protein concentration (Table 2). Commercial diets were chosen for practical relevance of the study, and the difference in Se concentration and other parameters (e.g. ingredients, processing conditions, Se species) between the canned and kibble diets are considered inherent to the diet types. For every diet type, diets with an estimated (from the pet food labels) crude protein concentration of 9.6, 14.3, 19.1 and 23.9 g CP/MJ ME (40, 60, 80 and 100 g CP/1000 kcal ME, resp.) were included. Four different protein concentrations were selected, rather than diets with different protein digestibility coefficients. This resulted in a range of the absolute amount of digestible protein, as the limited differences in protein digestibility in commercially available diets are usually overruled by the protein concentration per se. All diets were single-batch, to prevent differences in nutrients over time due to variations in ingredients. Selected canned diets were Royal Canin^® Canine Veterinary Diet Hepatic, Sensitivity Control Duck & Rice, and Recovery and Canine Veterinary Care Nutrition Senior Consult Mature. Selected kibble diets were Royal Canin^® Canine Veterinary Diet Renal, Gastro Intestinal Moderate Calorie, and Satiety Weight Management and Canine Veterinary Care Nutrition Pediatric Junior Large Dog. The canned diets contained Se solely from the ingredients, which is primarily organically-bound Se [34], whereas Se in the form of sodium selenite was supplemented in all kibble diets before processing (standard, not specifically for this study). Supplemented amounts of sodium selenite were 0.05, 0.08, 0.08, and 0.08 mg/kg, respectively. As veterinary diets were used in this study, some of the diets were supplemented with additional nutrients in order to be nutritionally complete and balanced for healthy adult dogs with energy requirements of 397 kJ (95 kcal)/kg BW^0.75. Details of the supplementation are included in Table 2. Each dog was fed individually to maintenance requirements.

MJ, megajoule; ME, metabolisable energy

^a All diets were supplemented with 516 mg choline/dog/day, Choline chloride 78% solution, Taminco BVBA, Gent, Belgium

^b Supplemented with 89.7 mg magnesium/dog/day, Super magnesium, Metabolics Ltd, Eastcott, Wiltshire, England

^c Supplemented with 206.3 mg magnesium/dog/day, Super magnesium, Metabolics Ltd, Eastcott, Wiltshire, England

^d Supplemented with 2.2 mg copper/dog/day, Copper citrate, Metabolics Ltd, Eastcott, Wiltshire, England

^e Supplemented with 4.4 mg copper/dog/day, Copper citrate, Metabolics Ltd, Eastcott, Wiltshire, England

^f Supplemented with 3.8 μg vitamin D/dog/day, Pet-Cal^™, Pfizer Animal Health, New York, USA

^g Supplemented with 0.43 mg iodine/dog/day, Iodine 11, Metabolics Ltd, Eastcott, Wiltshire, England

^h Supplemented with 1.19 g methionine/dog/day, synthetic methionine, Evonik Industries, Essen, Germany

ⁱ Supplemented with 1.03 g methionine/dog/day, Evonik Industries, Essen, Germany

* The diets are from left to right: Royal Canin^® Canine Veterinary Diet Hepatic, Sensitivity Control Duck & Rice, Canine Veterinary Care Nutrition Senior Consult Mature, Canine Veterinary Diet Recovery, Renal, Gastro Intestinal moderate calorie, Canine Veterinary Care Nutrition Pediatric Junior Large Dog and Canine Veterinary Diet Satiety Weight Management

^† Obtained from the pet food producer

^‡ Calculated using predictive equations for ME [21]