Modelling net energy of commercial cat diets.

Net energy accounts for the proportion of energy expenditure attributed to the digestion, metabolism, and absorption of ingested food. Currently, there are no models available to predict net energy density of food for domestic cats. Therefore, the objectives of this study were to measure the heat increment of feeding in cats, and to model the net energy of commercial diets. Metabolizable energy and calorimetry data from two previous studies was reanalyzed to create net energy models in the present study. Energy expenditure was calculated using measurements of CO2 production and O2 consumption. Net energy was determined as the metabolizable energy of the diets minus the heat increment of feeding. The heat increment of feeding was determined as the area under the energy expenditure curve above the resting fed metabolic rate. Eight net energy models were developed using metabolizable energy, 1 of 4 dietary parameters (crude protein, fat, fiber, and starch), and heat increment of feeding values from 0-2 h or 0-21 h. Two hours postprandial, and over the full calorimetry period, the heat increment of feeding amounted for 1.74, and 20.9% of the metabolizable energy, respectively. Of the models tested, the models using crude protein in combination with metabolizable energy as dietary parameters best fit the observed data, thus providing a more accurate estimate of dietary energy availability for cats.

Carbohydrate level and source have minimal effects on feline energy and macronutrient metabolism.

The carnivorous nature of the domestic cat makes feline metabolism of carbohydrates unique. The cats' glycemic response has been previously studied, with variable outcomes in response to carbohydrate level and source, but is an important response to understand how to control glycemia. The objectives of this study were to determine the glucose and insulin responses of cats fed 3 commercial diets differing in carbohydrate content and source, and to investigate the effects of diet on RQ, energy expenditure (EE), and glycemic response. Domestic shorthair cats (=19, 10 males, 9 females) of similar age (4.3 ± 0.48 yr, mean ± SD) and of ideal body condition score were used. Cats were fed, once a day, 1 of 3 commercial diets that differed in their perceived glycemic response (PGR; 36.8%, 30.7%, and 23.6% starch for high, medium, and low PGR, respectively) with cats cycling through all diets in 3 periods in 6 complete and 1 incomplete 3 × 3 Latin square. Each period consisted of 8 d of adaptation to the diet, followed by 21-h calorimetry measurements, and real-time interstitial glucose measurements on day 9. On day 10, sequential blood sampling was completed to determine blood glucose and insulin. BW and ME intake did not differ among treatments. EE in the fasted state did not differ among treatments (P = 0.160), whereas postprandial EE was highest for the high PGR diet compared with the medium PGR and low PGR diets (P < 0.001). In conclusion, cats revealed a prolonged postprandial glucose and insulin response compared with other monogastric animals, yet diet effects were minimal. Overall, interstitial glucose measures were less variable than serum glucose measurements and followed a parallel pattern to RQ. Therefore, going forward, calorimetry and continuous interstitial glucose monitoring should be considered as less invasive alternatives to repeated blood sampling.

Digestibility Is Similar between Commercial Diets That Provide Ingredients with Different Perceived Glycemic Responses and the Inaccuracy of Using the Modified Atwater Calculation to Calculate Metabolizable Energy.

Dietary starch is required for a dry, extruded kibble; the most common diet type for domesticated felines in North America. However, the amount and source of dietary starch may affect digestibility and metabolism of other macronutrients. The objectives of this study were to evaluate the effects of 3 commercial cat diets on in vivo and in vitro energy and macronutrient digestibility, and to analyze the accuracy of the modified Atwater equation. Dietary treatments differed in their perceived glycemic response (PGR) based on ingredient composition and carbohydrate content (34.1, 29.5, and 23.6% nitrogen-free extract for High, Medium, and LowPGR, respectively). A replicated 3 × 3 Latin square design was used, with 3 diets and 3 periods. In vivo apparent protein, fat, and organic matter digestibility differed among diets, while apparent dry matter digestibility did not. Cats were able to efficiently digest and absorb macronutrients from all diets. Furthermore, the modified Atwater equation underestimated measured metabolizable energy by approximately 12%. Thus, the modified Atwater equation does not accurately determine the metabolizable energy of high quality feline diets. Further research should focus on understanding carbohydrate metabolism in cats, and establishing an equation that accurately predicts the metabolizable energy of feline diets.