An integrative assay to quantify the nutritional quality of the selected diet of two Mediterranean free-living deer by faecal-FT-NIRS

Abstract

Integrating the interaction between cell wall components through a lignin and neutral detergent fibre ratio as a cell wall digestibility (CWD) index may provide a suitable method for diet quality and fibre digestibility estimation. Predictive faecal-Fourier-transform (FT)-near infrared reflectance spectroscopy (NIRS) equations useful for CWD determination were developed as an integrative assessment of the digestibility and quality of the diet selected by red (Cervus elaphus hispanicus) and fallow (Dama dama) deer in southern Spain. A chemometric regression was used from spectra of faeces and wet chemical rumen contents analysis as reference data coupled with partial least-squares. The accuracy and feasibility of the equations obtained for red and fallow deer samples separately were evaluated, as well as after pooling all samples for both species. The predictive equations had a high linearity with correlation coefficients (r) ranging between 0.89 and 0.99, as well as a reliable accuracy considering the errors of prediction (RMSEP 0.57–0.87), calibration (RMS 0.04–0.45) and cross-calibration (RMSECV 0.80–1.12) in relation to the range of values for which the NIRS calibration was set for each parameter, giving very good RER (residual error value) indices (7.44–13.23). The ability of the calibration equations to predict new samples from the same deer populations was also assessed through an external validation. Equations obtained for the red deer data were successfully applied not only to red deer but also to fallow deer, and vice versa. Feasible CWD simultaneous determination in red and fallow deer was also obtained by using the broad-based equations. There was variation of the CWD index throughout the year and differences between the two deer species. A lower CWD of the forage was recorded in red deer, while a lower CWD ratio was detected at the end of winter coinciding with the highest browsing levels in both species. This technique has potential to enable closer examination of the non-grass variables and distinguish between browse and herbage feeding behaviour. The faecal-NIRS method of CWD ratio determination is a useful, non-invasive tool for monitoring variations in the diet quality of Mediterranean deer in their natural environment.