In vivo and in vitro digestibility, palatability and nutritive quality of extruded dog food based on mechanically separated chicken meat or meat by-product

Fresh meat, such as mechanically separated chicken meat (MSCM), is usually listed first as an ingredient on pet food labels when selected by industry as a protein component. This commercial strategy may influence consumer choice in the comparison among pet food products. Since most dry pet foods are produced by food extrusion, it is important to compare the nutritional value of a dog diet based on MSCM with one based on meat by-products (MBP), such as processed animal proteins, to determine whether the "fresh meat" is the better choice. The objectives of this study were: (a) to evaluate the effect of inclusion of MSCM in dry dog food on fatty acid (FA) profile, in vivo and in vitro digestibility, and palatability as compared with dry dog food containing MBP; (b) to determine, whether or not, the inclusion of the one or the other ingredient changes the microbiology and the storage quality of the two food products; (c) to propose a new system (DaisyII Incubator) to measure the in vitro digestibility of the two products. Despite their similar chemical composition, the MSCM product had lower palatability but better nutritional quality (with higher polyunsaturated FA content and lower saturated FA content) than the MBP product. The n-6/n-3 polyunsaturated FA ratio was 11.5 and 16.7 for the MSCM and the MBP diet, respectively. Microbiological risk assessment showed no microbiological hazards for either product. After 6 months storage, the total mesophilic bacterial count ranged between 1.77 log CFU/g and 2.09 log CFU/g feed, while polyamine values were found to be higher in the MSCM (0.37 g/kg) than in the MBP (0.27 g/kg). Our results indicate that MSCM or MBP may be advantageously included in pet food formulation as a source of animal protein. Moreover, the DaisyII Incubator proved a valid instrument for the study of in vitro digestibility for dogs. Since it provided data simply, quickly, with less variability and cost than obtained with in vivo trials, it could represent the future for pet food digestibility studies.