Polyethylene glycol, determined by near-infrared reflectance spectroscopy, as a marker of fecal output in goats.

We report the application of NIR spectroscopy to determine the fecal concentration of poly(ethylene glycol) (PEG, MW 6000) used as an external marker of fecal output in goats. Calibration was carried out, using the modified partial least-squares method (MPLS), combining all wavelengths in the 1100-2500 nm range, with high linearity (R2 = 0.99). In goats fed at maintenance level, the recovery of PEG in feces was complete, and the estimation of fecal output was accurate, when a moderate dose of PEG was given (20 g/d). A higher dose of PEG (40 g/d) was associated with underestimation of fecal output, probably because PEG interacted with water metabolism. Using PEG and its NIRS-aided analysis to determine fecal output is accurate, simple, and cheap. However, the feasibility of this new method must be verified in goats feeding on tannin-containing diets, and in goats at high feeding level.