Mid-infrared (MIR) milk analyzers are traditionally calibrated using sets of preserved raw individual producer milk samples. The goal of this study was to determine if the use of sets of preserved pasteurized modified milks improved calibration performance of MIR milk analyzers compared with calibration sets of producer milks. The preserved pasteurized modified milk sets exhibited more consistent day-to-day and set-to-set calibration slope and intercept values for all components compared with the preserved raw producer milk calibration sets. Pasteurized modified milk calibration samples achieved smaller confidence interval (CI) around the regression line (i.e., calibration uncertainty). Use of modified milk calibration sets with a larger component range, more even distribution of component concentrations within the ranges, and the lower correlation of fat and protein concentrations than producer milk calibration sets produced a smaller 95% CI for the regression line due to the elimination of moderate and high leverage samples. The CI for the producer calibration sets were about 2 to 12 times greater than the CI for the modified milk calibration sets, depending on the component. Modified milk calibration samples have the potential to produce MIR milk analyzer calibrations that will perform better in validation checks than producer milk-based calibrations by reducing the mean difference and standard deviation of the difference between instrument values and reference chemistry.
Our objective was to determine the validation performance of mid-infrared (MIR) milk analyzers, using the traditional fixed-filter approach, when the instruments were calibrated with producer milk calibration samples vs. modified milk calibration samples. Ten MIR analyzers were calibrated using producer milk calibration sample sets, and 9 MIR milk analyzers were calibrated using modified milk sample sets. Three sets of 12 validation milk samples with all-laboratory mean chemistry reference values were tested during a 3-mo period. Calibration of MIR milk analyzers using modified milk increased the accuracy (i.e., better agreement with chemistry) and improved agreement between laboratories on validation milk samples compared with MIR analyzers calibrated with producer milk samples. Calibration of MIR analyzers using modified milk samples reduced overall mean Euclidian distance for all components for all 3 validation sets by at least 24% compared with MIR analyzers calibrated with producer milk sets. Calibration with modified milk sets reduced the average Euclidian distance from all-laboratory mean reference chemistry on validation samples by 40, 25, 36, and 27%, respectively for fat, anhydrous lactose, true protein, and total solids. Between-laboratory agreement was evaluated using reproducibility standard deviation (s R ). The number of single Grubbs statistical outliers in the validation data was much higher (53 vs. 7) for the instruments calibrated with producer milk than for instruments calibrated with modified milk sets. The s R for instruments calibrated with producer milks (with statistical outliers removed) was similar to data collected in recent proficiency studies, whereas the s R for instruments calibrated with modified milks was lower than those calibrated with producer 2833 milks by 46, 52, 61, and 55%, respectively for fat, anhydrous lactose, true protein, and total solids.
Daily yields of milk, milk fat, phospholipids, and fatty acids were measured weekly during lactations of two groups of cows on a normal and restricted roughage diet. Milk yield was higher in normal cows during the initial 15 wk of lactation. Fat production decreased and was consistently lower in milk from cows on restricted roughage (from 1.2 to .4 in normal and from .8 to .3 kg/day for restricted). Phospholipid secretion decreased from an average 7 g to 3 g/day in both groups. The concentration of phospholipid in both milks fluctuated during lactation (20 to 30 mg/100 ml milk), but in milks from restricted cows it tended to increase with progress of lactation. Milk lipids from cows on restricted diets had higher phospholipid to fat ratio, (1.0 to 1.5 compared to .5 to .6 g phospholipid/100 g fat for milk from normal cows). Composition of the phospholipid classes changed slightly during lactation. Phosplatidylinositol changed most, increasing from 4 to 10 and 6 to 8% in normal and restricted milks, respectively. Fatty acids of short and medium chain lengths (C6 to C14) followed a typical quadratic regression in normal milks increasing from 10 to 30% of the total fatty acids during the first 25 wk of lactation. In restricted milk these fatty acids were already high (25%) within 2 wk and followed a linear regression with lactation. Both palmitic and stearic acid were lower in milk from restricted cows while oleic and linoleic acid were higher particularly after 10 wk of lactation.
The use and performance of a computer-controlled apparatus for certification of Babcock bottles used for payment testing were evaluated. The apparatus delivered mercury into the bottle neck using a syringe mounted on a motorized pump. Syringe movement and the collection and calculation of data were controlled by computer. The apparatus was evaluated using four 8% milk bottles (total volume 1.600 mL; bottles rejected if deviation was ≥0.008 mL) and four 50% short-neck cream bottles (total volume 5.000 mL; bottles rejected if deviation was ≥0.050 mL). Six milk and 5 cream bottle trials were conducted; each bottle was read 5 consecutive times for each trial. As a percentage of the rejection criteria, average repeatability was 5–6% and reproducibility was 9–10%. These values were similar for both types of bottles. The evaluation of the apparatus demonstrated acceptable within- and between- days performance in relation to the rejection criteria and volumes measured. Because the apparatus creates a closed system during certification, an additional experiment was conducted with 50% short-neck cream bottles to determine the effect of internal pressure within a bottle on volume estimates. Four trials were conducted, as previously described, using 4 control and 4 experimental bottles. Volume between the 0 and 50% marks (5 mL) was determined. Holes were drilled in the experimental bottles to eliminate internal pressure for the final 2 trials. The estimated volume of bottles under pressure was 0.0054 ± 0.0012 mL greater than without internal pressure (i.e., about 11% of the rejection criteria). We concluded that any pressure effect was small relative to other factors that affect volume determination.
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