Determination of the concentration of a component in one fluid of an animal by spectroscopic analysis of another fluid

A method for calibrating an infrared spectroscopy apparatus in order to produce spectra with a view to determining the concentration of a component C1 in a fluid F1 of an animal, said method comprising:

• a) obtaining samples of said fluid F1 and of a fluid F2 other than the fluid F1 from each animal belonging to a group of representative animals, the fluid F2 containing detectable amounts of at least one component C2 which is directly or indirectly related to a metabolic pathway of the component C1,
• b) measuring the concentration of the component C1 in the samples of fluid F1 by means of a reference method,
• c) producing the complete IR absorption spectrum of the sample of fluid F2 in the frequency range from 650 cm−1 to 4000 cm−1,
• d) identifying in the absorption spectra of the samples of fluid F2, obtained in c), the spectral ranges that are correlated with the concentration of the component C1 in the samples of fluid F1, and
• e) calculating, on the basis of at least one of said correlated spectral ranges, a predictive mathematical model of the concentration of the component C1 in the fluid F1.