Appraisal of ingestion and digestibility in growing rabbits using near infrared reflectance spectroscopy (NIRS) of feeds and faeces

The aim of this work was to examine whether faecal profiling using NIRS could be profitable for promote the Best Available Techniques (BAT) in the rational feeding of rabbits. A set of 51 feed samples, taken from 12 experimental diets, and of 66 dried grouped faeces samples, belonging to four nutrition experiments, with 130 ad libitum registered feed intakes (CV=25%), were submitted to a UV-Vis-NIRS scan (350-2500 nm) in order to calibrate the chemical composition and nutritional parameters, the ingestion aptitude and digestibility. A chemometric system has made it possible to contemporary use the spectrum of the input diet concatenated together with the spectra of the related output pool of the dried faeces. The daily measured feed intake, in absolute or in relative terms as ingestion per unit of metabolic weight, obtained a good resolution for the spectra of the feeds (R2 cv=0.80 and 0.75, respectively), for the faeces (0.81 and 0.80) and for the joint evaluation of the concatenated spectra (0.87 and 0.81). The intake was positively correlated to the mineral, insoluble ash, protein, gross energy, crude fiber and acid detergent fiber (ADF) content in the feeds, and negatively correlated to the N-free extract, lignocellulose and all the digestibility coefficients, except crude fiber. Very significant improvements, on average equal to 0.20 R2 points, were also provided to the digestibility coefficients when using the concatenated method; in decreasing order: neutral detergent fiber (R2 cv=0.00, 0.18 and 0.50 for the feeds, faeces and concatenated, respectively), ADF (0.00, 0.45 and 0.62), ether extract (0.53, 0.52 and 0.86), crude protein (0.53; 0.53 and 0.75), and gross energy (0.61; 0.74 and 0.83). The results corroborate previous knowledge and show the possibility of using NIRS faecal profiling in rabbit nutrition, which together with the NIRS of the feeds, could contribute to nitrogen monitoring.