Milk Nitrogenous Components as Measured by Near Infrared Spectroscopy-study on the repeatability for Predicting Different Population Samples

Abstract

The study on the use of near infrared reflectance spectroscopy (NIRS) analysis for measuring milk nitrogenous components (crude protein, true protein, casein and milk urea nitrogen (MUN)) was carried out using one hundred seventy milk samples collected from lactating Holstein cows used in three feeding experiments. Experiment 1 consisted of ninety-six milk samples using sixteen mid-lactation cows fed a basal ration containing corn silage, Italian ryegrass wafer, Alfalfa haycube, corn flake and commercial concentrate with four kinds of supplementation, (I) corn gluten meal (CGM), (2) fish meal (FM), (3) roasted soybean meal (RSBM) , and (4) defatted soybean meal (SBM) for each four animals. Experiment 2 consisted of forty-two milk samples from seven early lactation cows raised under total mixed ration (TMR) feeding management containing corn silage, Timothy hay and concentrate. Experiment 3 consisted of thirty-two milk samples from eight early lactation cows raised under two rations feeding management, (I) basal ration supplemented with SBM, and (2) basal ration supplemented with mixed of SBM and FM. Basal ration in this experiment was similar with that given in experiment l. The samples from experiment I and 2 were randomly separated into two groups, (1) calibration set samples (n = 84), (2) validation set samples (n = 54), while the milk samples from experiment 3 were grouped as (3) application set samples. These groups were used for developing calibration equations, validating the equations, and for evaluating the reproducibility when the calibration equations were employed to samples from different population. Using four combinations of wavelengths at 1650, 1698, 1738 and 1756 nm, the accuracy and reproducibility of measurements were high for crude protein, true protein and casein, but not for MUN. Animal Science Journal 70 (5) : 343-348, 1999 Key words: NIRS, Milk nitrogen components, MUN