Predicting Chemical Composition and Apparent Total Tract Digestibility on Freeze-Dried Not Ground Faeces Using Near-Infrared Spectroscopy in Pigs

Near-infrared reflectance spectroscopy (NIRS) is widely used to predict the nutritional value of raw materials and complete feeds in feed mills. Recently, faecal NIRS was proposed as a fast and cheap method to predict nutrient digestibility to partially replace in vivo digestibility trials. Previous studies used freeze-dried ground (FDG) faeces via NIRS, but the use of not ground (FDNG) faeces could save time and workload. The objective of the present study was to compare the results obtained with NIRS using faecal samples in two forms, FDNG and FDG, to predict faecal chemical composition and apparent total tract digestibility (ATTD) coefficients. Faecal samples were collected from grower-finisher pigs at pen level, freeze-dried, and analysed via NIRS as FDNG and FDG faeces. NIRS calibrations were developed and successfully predicted faecal chemical components and ATTD coefficients of nutrients for both FDNG and FDG faeces. Thus, faecal NIRS is a potential tool to evaluate faeces' chemical components and ATTD coefficients of nutrients, and those are successfully predicted using FDNG faeces, saving analysis time and workload. The present study aimed to compare NIRS results using freeze-dried ground or not ground (FDG or FDNG) faeces to predict faecal chemical composition and apparent total tract digestibility (ATTD) coefficients. Two different batches of pigs were used (n = 20 mixed sex pens/batch; 11 pigs/pen; Duroc × (Large White × Landrace)). The first batch of pigs (B1; 50.1 ± 3.44 kg body weight (BW)) was used at 13 wks of age and the second batch (B2; 87.0 ± 4.10 kg BW) was used at 18 wks of age. For both B1 and B2, pens were assigned to five diets formulated to obtain a control [10.03 MJ of net energy (NE), 160.0 g of crude protein (CP), and 9.5 g of standardized ileal digestive (SID) lysine (Lys) per kg of feed], low protein (132.0 g CP and 7.5 g SID Lys), high protein (188.0 g CP and 11.5 g SID Lys), low energy (9.61 MJ NE/kg), and high energy (10.45 MJ NE/kg) diets. After a 10-day adaptation period, one faecal sample was collected daily from each pen floor during 6 days in both B1 and B2 (n = 120/batch). Faecal samples were freeze-dried and analysed via NIRS as FDNG and FDG faeces. Dry matter (DM), organic matter (OM), CP, gross energy (GE), fat, and ATTD coefficients were analysed/calculated. The NIRS calibrations were evaluated by cross-validation, splitting the data in four random groups, or using the leave-one-out method. For both FDNG and FDG faeces, coefficients of determination for calibration (R 2 ) and residual predictive deviation (RPD) values were: close to 0.9 and 3 for DM and CP, 0.7-0.8 and ≥2 for OM and GE, 0.6 and <2 for fat, and 0.54-0.75 and ≤2 for ATTD coefficients, respectively. CP was better predicted using FDG faeces (p < 0.05), while DM and OM ATTD were better predicted using FDNG faeces (p < 0.05). In conclusion, NIRS successfully predicts faeces' chemical components and ATTD coefficients of nutrients using FDNG or FDG faeces.