Cashew (Anacardium occidentale) nut co-product in extruded foods for dogs

Cashew nut is a co-product of the cashew (Anacardium occidentale) industry, with high fat (40%) and protein (23%) contents. During processing, the nuts can break down, generating the cashew nut granules (CNG). Considering the effort for rational use of food resources, the present study investigated the use of CNG as an ingredient in extruded dog diets. Four formulations with similar chemical compositions were used, a control (CO) based on poultry by-product meal and poultry fat, and three inclusion levels of CNG as protein and fat source: 2.5%, 5%, and 10% (on an as-fed basis). Due to its high fat content, the implications of CNG to the extrusion process was investigated. Twenty-four beagle dogs were used to determine total tract apparent digestibility (TTAD), faeces characteristics and fermentation products, and a panel of 39 dogs were used for palatability comparisons. The results of extrusion, TTAD, and faecal traits were submitted to variance analysis and means compared by polynomial contrasts according to the CNG inclusion level (p < 0.05). In the palatability test, the first intake was compared by the Qui-square test and the intake ratio by the Student's t-test (p < 0.05). The CNG addition increased the internal fat content of the raw material mixture from 9.5% to 12.6%. This induced a linear reduction in mechanical energy transference, which in turn reduced mass pressure and temperature at extrusion (p < 0.01), which compromised kibble formation with lower expansion and higher density (p < 0.01). Starch gelatinisation did not reduce but in fact increased, explained by a linear increase in thermal energy application (p < 0.01). The TTAD of nutrients did not differ between diets (p > 0.05). Faeces pH, production and score did not differ among treatments (p > 0.05). Acetate, butyrate, and lactate increased quadratically (p < 0.01) in the faeces, with higher values for animals fed the 2.5% CNG feed. In the palatability test, only CO, 2.5% CNG and 5% CNG treatments were compared, and diets with CNG had higher preference than CO (p < 0.01). By conclusion, up to 10% inclusion of CNG did not alter TTAD of nutrients or faeces formation and increased diet palatability, supporting the use of this co-product in extruded diets for dogs.