Faecal Indices Based on near Infrared Spectroscopy to Assess Intake, in vivo Digestibility and Chemical Composition of the Herbage Ingested by Sheep (Crude Protein, Fibres and Lignin Content)

Abstract

The aim of this study was to evaluate the potential of faecal indices based on near infrared (NIR) spectroscopy to assess chemical composition and functional properties (intake and in vivo digestibility) of fresh grass ingested by sheep. Reference data and faecal spectra were obtained from a pen experiment with 12 ewes individually housed and fed fresh Digitaria decumbens at varying stages of re-growth (14–63 days) during a period of 49 days. The amount of herbage offered, refused and faecal excretion were measured per ewe daily. Organic matter (OM) content, crude protein (CP) content, neutral and acid detergent fibre (NDF, ADF) and acid detergent lignin (ADL) content were dosed in offered, refused and faecal samples. OM digestibility (OMD), intake (OMI) and chemical composition of the herbage ingested (OMi, CPi, NDFi, ADFi, ADLi, % dry matter) were calculated per ewe and per seven days. Faecal samples were bulked within each seven days of measurement period, per ewe. Eighty four dried and milled faecal samples were scanned using a monochromator. Faecal spectra were used to calibrate and cross-validate equations for predicting the various parameters using the modified partial least square (MPLS) procedure. For the CP content of the herbage really ingested (CPi), derived standard error of cross-validation ( SECV) and cross-validation R2 ( R2cv) were 0.61% and 0.98. For NDFi, ADFi and ADLi, the values of SEC-V and R2 cv were, respectively, 1.64% and 0.45, 0.78% and 0.91 and 0.34% and 0.77. For OMD, the values of SECV and R2 cv were 2.02% and 0.77, whereas lower calibrations statistics were obtained for OMI (11.04 g kg BW–0.75 and 0.45). These values confirmed the potential of NIR Spectra of faeces as a technology for reliably predicting the in vivo digestibility and chemical quality of herbage really ingested and estimating the herbage intake by small ruminants.