Fermentable fibres are used in commercial dog food to promote intestinal health by providing substrates for better metabolic activity of the gut microbiota. Brazil is the world’s largest producer of oranges, from which it is possible to obtain fibre with a relevant soluble fraction. The present study compared the effects of two inclusions of orange fibre (1% and 3%, on as fed basis) with a negative control (without addition of fibre source) and two positive controls, beet pulp (3%) and purified inulin (1%), totalling five extruded diets for dogs. The experiment followed a randomised block design with 4 blocks of 10 dogs, 2 dogs per food in each block, totalling 8 dogs per diet. The apparent total tract nutrient digestibility was determined by total faecal collection. Faecal pH and fermentation product content were also measured. The digesta mean retention time (DMRT) was evaluated using plastic markers. The inclusion of a 3% fibre source in diets with 3% orange fibre and beet pulp reduced DM, OM, and energy digestibility (p < 0.05). Diets with 3% orange fibre, beet pulp and 1% inulin presented lower crude protein digestibility than the control (p < 0.05). Dietary fibre digestibility was higher for orange fibre-supplemented diets than inulin (p < 0.05). Beet pulp and 3% orange fibre inclusions resulted in increased moisture content in the faeces of dogs (p < 0.05) but did not alter DMRT. Total short-chain fatty acids were higher than the control in the faeces of dogs fed both orange fibre levels and the beet pulp-supplemented diet (p < 0.05), and the inulin diet-fed dogs presented intermediate values. Butyrate was higher in the faeces of dogs fed the diets supplemented with 1% and 3% orange fibre (p < 0.05), and similar values to the control were observed for beet pulp- and inulin-fed animals. Thus, it was concluded that orange fibre presented higher apparent total tract dietary fibre digestibility than beet pulp and had a fermentation profile in the colon that promoted the generation of butyrate, an effect not observed for inulin and beet pulp.

Determining protein requirements (PRs) for dogs remains a longstanding challenge. During growth, the rapid rate of protein deposition increases the demand for amino acids. In adult dogs, differences in overall diet digestibility and lower energy requirements of domestic dogs have led to discrepancies between the minimum crude protein (CP) value proposed by the National Research Council (NRC; 80 g of CP/kg of diet) and the 180 g of CP/kg of diet proposed by the European Pet Food Industry Federation (FEDIAF) and the Association of American Feed Control Officials (AAFCO), although most commercially available adult dog feeds offer protein levels that exceed both recommendations. In elderly dogs, physiological changes such as sarcopenia and reduced energy intake indicate a potential increase in PR, although evidence remains scarce. A similar gap exists for pregnant and lactating bitches, since most recommendations rely on extrapolations from growth studies. Classical PR recommendations were based on body weight gain and nitrogen balance (NB), methods that present important limitations. Due to this, stable isotope methods—including ¹³C-leucine, ¹⁵N-glycine, and ¹³C-phenylalanine—have emerged as precise methodological tools, enabling a detailed and dynamic assessment of whole-body protein metabolism, protein quality, and more accurate determination of PR and recommended allowance across different life stages.

Fiber supplemented extruded foods are produced by pet food companies to help with several specific health conditions. The fiber material, however, is difficult to incorporate efficiently into dry kibble diets for dogs. The aim of the study was to evaluate the influence of citrus pulp pellet (CPP), the solid waste part of the production of orange juice characterized by a good proportion of soluble and fermentable fiber, on extrusion traits, kibble macrostructure, starch gelatinization and in vitro digestibility of dog foods. A control formula (CO) was developed for dogs. CPP was added to CO at different inclusion levels: 5%, 10%, 15% and 20%. Foods were extruded in a single screw extruder using two different die diameters (d_d): 5 mm and 7 mm. CPP inclusion with 5 mm d_d did not affect bulk and piece density and resulted in a lower impact on kibble expansion; It also resulted in greater starch gelatinization and kibble expansion compared to the 7 mm d_d configuration (p < 0.01). In addition to the nutritional implications, recycling and proper uses of this material exemplified in the present study by the exploration of CPP as a fiber source to dogs, this method can improve sustainable agriculture by transforming low-quality materials into high-quality foods.

Determining protein requirements (PR) for dog maintenance using welfare-conscious methods is challenging. This study aimed to establish a minimally invasive and efficient protocol for applying the indicator amino acid oxidation (IAAO) technique using L-[1-13C] phenylalanine (13Phe), while minimizing animal handling and cost (through lower isotope doses and fewer meals) and eliminating the need for respiration chambers. Two diets were extruded: a complete and balanced for maintenance based on poultry by-product meal (PBM) with 28% crude protein (CP); a low-protein formulation where PBM was replaced by maize starch (SBD) with 6% CP (DM basis). Ingredients were analyzed, and the SBD was supplemented so both formulations presented 22 g/kg of phenylalanine + tyrosine (DM basis). The dilution technique was applied to create five levels of CP: 6%, 8%, 10%, 12%, and 14% (DM basis). A sixth diet with 11% CP was used in the adaptation period. To test three feeding, isotope-enrichment, and sampling protocols (P1, P2, and P3), a block design was used with 10 dogs assigned to each protocol (14.8 ± 1.1 kg; 5.8 ± 2.0 years). After two days of adaptation (11% CP), the daily dog food was divided into 10 (P1), 7 (P2), or 5 (P3) meals. A priming dose (PD) of 0.18 mg/kg of 13C-Bicarbonate (13Bic) and 0.66 mg/kg of 13Phe were offered on the fourth, sixth, or fifth meal, followed by six, four, and four subsequent doses of 1.33 mg/kg of 13Phe in capsules every 30 min (P1, P2, and P3, respectively). Two basal samples of expired air were collected using an adapted mask, and after PD, eight samples were collected, starting 30 (P1), 90 (P2), and 90 (P3) min after enrichment. The CO2 volume was measured by the 13Bic method using masks. The time required to reach isotopic steady state (ISS) and the accuracy of measurements varied across protocols. P1 required the longest time to reach ISS (183.7 ± 8.4 min) and showed lower accuracy (r2 = 0.39; mean absolute percentage error [MAPE] = 17.1%; P < 0.05). P3 reached ISS more quickly (105.4 ± 6.1 min) but demonstrated moderate accuracy (r2 = 0.67; MAPE = 7.1%; P < 0.05). P2 represented an intermediate condition, reaching ISS at 170.6 ± 6.7 min while providing higher accuracy (r2 = 0.81; MAPE = 1.26%; P < 0.05). It was concluded that P2 is a minimally invasive and efficient protocol for IAAO application in dogs, potentially providing valuable insights for future research involving dogs living outside of a laboratory setting.

Hydrolysed proteins have been shown to be potential ingredients in cat diets due to their high digestibility, presence of bioactive peptides, and relatively low antigenicity. The effects of the substitution of conventional low ash poultry byproduct meal (PBM) with hydrolysed poultry byproduct meal (HPM) as a protein source were evaluated in extruded cat diets. Five diets with similar nutrient contents were formulated: a control (CO) diet based on PBM and 4 diets with different inclusions of HPM (5%, 10%, 20%, and 30%, on an as-fed basis) replacing PBM as the protein source. The total tract apparent digestibility (CTTAD) of nutrients, faecal characteristics and microbial fermentation products, urine production and pH, nitrogen balance and urea renal excretion were evaluated using 30 healthy cats (15 males and 15 females; 4.18 +/- 0.86 kg; 4.17 +/- 1.38 years old), with 6 cats per diet in a complete randomised block design. When significant differences were found with the F test, the effects were evaluated by polynomial contrasts according to HPM inclusion (p < 0.05). The CTTADs of DM (89 +/- 0.41%), CP (90 +/- 0.36%), fat (93 +/- 0.41%) and gross energy (90 +/- 0.33%) were similar among treatments (p > 0.05). The faecal production, score, short-chain fatty acids and ammonia concentration were similar among treatments (p > 0.05). Isobutyric, isovaleric, valeric, and total branched-chain fatty acid contents increased quadratically (p < 0.05), with the highest level in the faeces of cats fed the diet with 20% HPM. Lactate concentration in faeces increased linearly with the inclusion of HPM (p < 0.05). Urine characteristics and urea renal excretion did not differ among treatments (p > 0.05). At 10% inclusion, HPM tended to increase the nitrogen retention of cats (p = 0.083), which may reflect the higher tryptophan, methionine, lysine, and available lysine contents of HPM in comparison to PBM. The inclusion of up to 30% HPM can be considered in cat formulations without affecting nutrient digestibility or faecal and urine characteristics. HPM tended to increase nitrogen retention and increased branched-chain fatty acids in faeces, aspects which deserves further studies.