Near infrared spectroscopic analysis of forage samples digested in situ (nylon bag)

Prediction of crude protein and neutral detergent fibre concentration in residues of in situ ruminal degradation of pasture samples by near-infrared spectroscopy (NIRS)

An important constraint of in situ degradability studies is the need to analyse a high number of samples and often with insufficient amount of residue, especially after the longer incubations of high-quality forages, that impede the study of more than one nutritional component. Near-infrared spectroscopy (NIRS) has been established as a reliable method for predicting composition of many entities, including forages and other animal feedstuffs. The objective of this work was to evaluate the potential of NIRS for predicting the crude protein (CP) and neutral detergent fibre (NDF) concentration in rumen incubation residues of permanent and sown temperate pastures in a vegetative stage. In situ residues (n = 236) from four swards were scanned for their visible-NIR spectra and analysed for CP and NDF. Selected equations developed by partial least-squares multivariate regression presented high coefficients of determination (CP = 0.99, NDF = 0.95) and low standard errors (CP = 4.17 g/kg, NDF = 7.91 g/kg) in cross-validation. These errors compare favourably to the average concentrations of CP and NDF (146.5 and 711.2 g/kg, respectively) and represent a low fraction of their standard deviation (CP = 38.2 g/kg, NDF = 34.4 g/kg). An external validation was not as successful, with R2 of 0.83 and 0.82 and a standard error of prediction of 14.8 and 15.2 g/kg, for CP and NDF, respectively. It is concluded that NIRS has the potential to predict CP and NDF of in situ incubation residues of leafy pastures typical of humid temperate zones, but more robust calibrations should be developed.

The use of near infrared analysis for in situ studies

This study evaluated the use of near infrared reflectance spectroscopy to estimate the chemical composition of feed residues after in situ ruminal incubation. Residues of three alfalfa hays (n = 93) and three alfalfa pellets (n = 93) obtained after ruminal exposure were analyzed for dry matter, crude protein, neutral detergent fiber, acid detergent fiber, and acid detergent lignin by wet chemistry and were also scanned with a near infrared monochromator instrument. A calibration was calculated that combined hay and pellet samples (n = 60). Validation tests were performed using the remaining feed residues. The coefficients of determination and standard errors (percentage of dry matter) of the validation tests for crude protein, neutral detergent fiber, acid detergent fiber, and lignin were of 0.95 and 0.92, 0.96 and 1.68, 0.95 and 1.56, and 0.99 and 0.48, respectively. Similar statistics were obtained using the SELECT algorithm of sample selection; a further 30% reduction was observed in the number of samples that were used for calibration. Kinetics of ruminal degradation and effective degradabilities that were calculated based on chemical composition of the residues as determined by wet chemistry or estimated by near infrared reflectance spectroscopy were not significantly different for 68 out of 71 means. Differences in ruminal kinetics caused by the different forages were also unaffected by method of residue analyses. Near infrared reflectance spectroscopy allowed a reduction in the number of necessary laboratory analyses of feed residues without affecting the results of in situ studies.