Prediction error and repeatability of near infrared reflectance spectroscopy applied to faeces samples in order to predict voluntary intake and digestibility of forages by ruminants

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

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 (R²_cv) 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.

Use of near-infrared reflectance spectroscopy on feces to estimate digestibility and dry matter intake of dietary nutritional characteristics under grazing conditions in Colombian creole steers

Digestibility and intake are parameters difficult and expensive to estimate under grazing conditions; therefore, the aim of this study was to develop near-infrared reflectance spectroscopy (NIRS) calibrations applied to feces (F-NIRS) and evaluate their accuracy to predict dry matter digestibility (DMD) and dry matter intake (DMI) of Colombian creole cattle. Five digestibility trials using creole steers were conducted; indigestible neutral detergent fiber (iNDF) was used as internal marker and Cr₂O₃ and TiO₂ as external markers. A total of 249 forage and 396 fecal samples from individual animals were collected, dried, and grinded for conventional chemical analysis. For spectral analysis, fecal samples were pooled across collection periods (77 samples). Chemometric analysis was performed using WinISI V4.10 software applying the modified partial least squares method. Cross-validation was performed to avoid overfitting the models. The goodness-of-fit statistics considered were the coefficient of determination in cross-validation and prediction sets (R²cv and r², respectively) and the ratio performance deviation (RPD). Fecal NIRS calibrations developed for forage and supplement DMD showed a satisfactory fit (R²cv =0.87 and RPD=2.77 and R²cv=0.92 and RPD=3.50, respectively). The accuracy of fecal output equations using chromium (Cr) and titanium (Ti) was similar in terms of R²cv (0.92) and RPD (3.63 vs. 3.57). Total DMI equations using Ti performed better compared to Cr (R²cv = 0.82 vs. 0.78; RPD=2.41 vs. 2.17, respectively). The F-NIRS models were validated using a completely independent set of fecal samples showing a moderate fit (r²>0.8 and RPD>2.0). This study showed that F-NIRS is a feasible tool to predict DMD and DMI of creole steers under grazing conditions. However, previous to socialization, this requires an improvement in accuracy of the calibrated equations related to grazing animals in different production contexts.

Choices between red clover and fescue in the diet can be reliably estimated in heifers post-weaning using n-alkanes

Measuring diet choice in grazing animals is challenging, complicating the assessment of feed efficiency in pasture-based systems. Furthermore, animals may modify their intake of a forage species depending on its nutritive value and on their own physiological status. Various fecal markers have been used to estimate feed intake in grazing animals. However, plant-wax markers such as n-alkanes (ALK) and long-chain alcohols may provide reliable estimates of both dietary choices and intakes. Still, their use in beef cattle has been relatively limited. The present study was designed to test the reliability of the ALK technique to estimate diet choices in beef heifers. Twenty-two Angus-cross heifers were evaluated at both post-weaning and yearling age. At each age, they were offered both red clover and fescue hay as cubes. Following 3-week acclimation periods, daily intake of each forage species was assessed daily for 10 days. During the final 5 days, fecal grab samples were collected twice daily. The ALK fecal concentrations were adjusted using recovery fractions compiled from literature. Diet composition was estimated using two statistical methods. Post-weaning, dietary choices were reliably estimated, with low residual error, regardless of the statistical approach adopted. The regression of observed on estimated red clover proportion ranged from 0.85±0.08 to 1.01±0.09 for fecal samples collected in the p.m. and for daily proportions once averaged, respectively. However, at yearling age, the estimates were less reliable. There was a tendency to overestimate the red clover proportion in diets of heifers preferring fescue, and vice versa. This was due to greater variability in ALK fecal concentrations in the yearling heifers. Overall, the ALK technique provided a reliable tool for estimating diet choice in animals fed a simple forage diet. Although further refinements in the application of this methodology are needed, plant-wax markers provide opportunities for evaluating diet composition in grazing systems in cattle.

Technical note: Comparison of dry matter measurements from handheld near-infrared units with oven drying at 60°C for 48 hours and other on-farm methods

This study compared dry matter (DM) predictions of 3 handheld near-infrared spectrophotometer (NIRS) units (Moisture Tracker, Digi-Star Inc., Fort Atkinson, WI) to conventional oven drying at 60°C using 2 alfalfa and 2 corn silages. In addition, on-farm DM methods [microwave, Koster tester (Koster Moisture Tester Inc., Brunswick, OH), and food dehydrator methods] were also compared. Corn and alfalfa silages (1,600 g) obtained from the University of Wisconsin Dairy Cattle Center (DCC) and the Arlington Research Station (ARS) were analyzed for DM daily for 20 d. Two NIRS calibration methods were also tested within each unit. The DM predicted from the factory-preset calibrations was NIR_f. The adjusted DM prediction was NIR_a, where the average difference between oven-dried and NIR_f determined on duplicate forage samples for 3 d before the experiment was used as a bias adjustment for all subsequent DM determinations. The average predicted DM from the 20 scans was recorded as the forage DM. The process was repeated 3 times with each NIRS unit. Two 100-g subsamples of each forage were also oven-dried for 48 h at 60°C daily in a forced-air oven. Oven DM of ARS and DCC alfalfa silages were 37.3 ± 1.1% and 48.5 ± 1.9%, respectively (mean ± standard deviation). Oven DM of ARS and DCC corn silages were 34.7 ± 1.2% and 37.4 ± 0.5%, respectively (mean ± standard deviation). Dry matter determinations from NIR_f were on average 3.5 units higher than the oven DM values. The NIR_a DM predictions were on average 1.7 DM units lower than the oven DM values. Additionally, differences among the 3 NIR_f probe results were detected (43.1, 40.7, and 41.3% DM, respectively), but all other results were similar between probes. Determinations of DM by the microwave and food dehydrator were also similar with the 60°C, 48-h oven method, whereas the Koster tester was lower than the oven. The handheld NIRS units more accurately predicted DM content of the alfalfa silage but were not as accurate with corn silages when the factory preset calibrations were corrected for bias.

Fecal Near-Infrared Reflectance Spectroscopy Prediction of the Feed Value of Temperate Forages for Ruminants and Some Parameters of the Chemical Composition of Feces: Efficiency of Four Calibration Strategies

The forage feed value determined by organic matter digestibility (OMD) and voluntary intake (VI) is hard and expensive. Thus, several indirect methods such as near infrared reflectance (NIR) spectroscopy have been developed for predicting the feed value of forages. In this study, NIR spectra of 1040 samples of feces from sheep fed fresh temperate forages were used to develop calibration models for the prediction of fecal crude ash (CA), fecal crude protein (CP), fresh forage OMD, and VI. Another 136 samples of feces were used to assess these models. Four calibration strategies were compared: (1) species-specific calibration; (2) family-specific calibration; (3) a global procedure; and (4) a LOCAL approach. The first three strategies were based on classical regression models developed on different sample populations, whereas the LOCAL approach is based on the development models from selected samples spectrally similar to the sample to be predicted. The first two strategies use feces-samples grouping based on the species or the family of the forage ingested. Forage calibration data sets gave value ranges of 79-327 g/kg dry matter (DM) for CA, 65-243 g/kg DM for CP, 0.52-0.85 g/g for OMD, and 34.7-100.5 g DM/kg metabolic body weight (BW^0.75) for VI. The prediction of CA and CP content in feces by species-specific fecal NIR (FNIR) spectroscopy models showed lower standard error of prediction (SEP) (CA 15.03 and CP 7.48 g/kg DM) than family-specific (CA 21.93 and CP 7.69 g/kg DM), global (CA 19.83 and CP 7.98 g/kg DM), or LOCAL (CA 30.85 and CP 8.10 g/kg DM) models. For OMD, the LOCAL procedure led to a lower SEP (0.018 g/g) than the other approaches (0.023, 0.024, and 0.023 g/g for species-specific, family-specific, and global models, respectively). For VI, the LOCAL approach again led to a lower SEP (6.15 g/kg BW^0.75) than the other approaches (7.35, 8.00, and 8.13 g/kg BW^0.75 for the species-specific, family-specific, and global models, respectively). LOCAL approach performed on FNIR spectroscopy samples gives more precise models for predicting OMD and VI than species-specific, family-specific, or global approaches.

Tropical grasslands: A pivotal place for a more multi-functional agriculture

Tropical grasslands represent a pivotal arena for the sustainable intensification of agriculture in the coming decades. The abundant ecosystem services provided by the grasslands, coupled with the aversion to further forest destruction, makes sustainable intensification of tropical grasslands a high policy priority. In this article, we provide an inventory of agricultural initiatives that would contribute to the sustainable intensification of the tropical grassland agro-ecosystem, and we recommend a shift in the scientific priorities of animal scientists that would contribute to realization of a more agro-ecological and multi-functional agriculture in the world's tropical grasslands.