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 predict undigested neutral detergent fibre at 240 h of fermentation (uNDF240) and other fibre fractions in lactating dairy cattle faeces. A total of 130 faecal samples (600 g) were collected directly from the rectum of dairy cows randomly selected across the lactating groups of 6 herds located in northern Italy and fed grass/alfalfa hay forage based total mixed ration. Reference values were matched with FNIRS spectra. Prediction equations were developed for each trait using external validation. Our results showed that the calculated uNDF240 (DM basis) to ADL ratio in faeces averaged 2.84, ranging from 1.58 to 4.10. The similar ratio of acid detergent fibre (ADF) and uNDF240 to NDF (66-67%) indicated that potentially digestible NDF in faeces is mainly represented by hemicelluloses, whereas uNDF240 is mainly composed of lignin and cellulose. The coefficient of determination of external validation (R2V) of uNDF240 was 0.59 when expressed as percentage of DM and 0.36 when expressed as percentage of NDF, and the corresponding ratio performance deviation of external validation (RPD) values in validation were 1.52 and 1.26, respectively. Values of R2V ranged from 0.54 to 0.63 for fibre fractions and RPD in validation ranged from 1.45 (ADL, % DM) to 1.68 (ADF, % DM). Despite the low accuracy of the prediction models, this study contributes to the knowledge of the FNIRS application to uNDF240 and other fibre fractions in faeces. Further investigations with different diet composition should be addressed.