The use of near infrared spectroscopy to predict faecal indigestible and digestible fibre fractions in lactating dairy cattle

The objective of this study was to investigate the ability of faecal near infrared spectroscopy (FNIRS) to predictundigested neutral detergentfibre at 240 h of fermentation (uNDF240) and otherfibre fractions in lactatingdairy cattle faeces. A total of 130 faecal samples (600 g) were collected directly from the rectum of dairy cowsrandomly selected across the lactating groups of 6 herds located in northern Italy and fed grass/alfalfa hay foragebased total mixed ration. Reference values were matched with FNIRS spectra. Prediction equations were de-veloped for each trait using external validation. Our results showed that the calculated uNDF240 (DM basis) toADL ratio in faeces averaged 2.84, ranging from 1.58 to 4.10. The similar ratio of acid detergentfibre (ADF) anduNDF240 to NDF (66–67%) indicated that potentially digestible NDF in faeces is mainly represented by hemi-celluloses, whereas uNDF240 is mainly composed of lignin and cellulose. The coefficient of determination ofexternal validation (R2V) of uNDF240 was 0.59 when expressed as percentage of DM and 0.36 when expressed aspercentage of NDF, and the corresponding ratio performance deviation of external validation (RPD) values invalidation were 1.52 and 1.26, respectively. Values of R2Vranged from 0.54 to 0.63 forfibre fractions and RPD invalidation ranged from 1.45 (ADL, % DM) to 1.68 (ADF, % DM). Despite the low accuracy of the predictionmodels, this study contributes to the knowledge of the FNIRS application to uNDF240 and otherfibre fractions infaeces. Further investigations with different diet composition should be addressed.