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Accuracy of Milk Check for Obtaining Milk Weights and Samples in Dairy Herd Improvement Association Testing

Department of Veterinary and Animal Sciences, University of Massachusetts, Amherst

ABSTRACT

The Milk Check is a small portable plastic and stainless steel device which works on a proportionate-sampling principle for obtaining milk weights and samples for milk fat test from dairy cows milked on pipeline milking systems. Eight of these devices were tested for accuracy in two herds (different milking systems) with a minimum of 84 and a maximum of 138 individual milking samples taken on each device. The devices were evaluated for aceptability according to the standards adopted by the DHIA Coordinating Committee in March, 1967.

The over-all mean error in milk weight was +7.4%. The mean errors in the two herds were –4.4 and +19.1%, indicating that the herd or milking system had a drastic effect on the results. All devices were acceptable in the amount of bias found in repeated milkings of the same cow. However, none of the devices performed within the established limits in the amount of random error in deviations from true milk weights.

Statistical tests for skewness and kurtosis indicated that the weighing errors deviated significantly from the normal distribution in both these respects.

Only 73.5% of the Milk Check milk fat tests were within the required ±0.2% of the true test. In addition the distribution of deviations from true test differed significantly from random according to Chi-square, due to a surplus of positive deviations.

These results indicated that neither the milk weights nor milk fat per cents obtained from the Milk Check were sufficiently accurate for use in testing when evaluated according to Dairy Herd Improvement Association rules.

¹ Present address: Dairy Herd Improvement, Dairy Cattle Research Branch, AHRD-ARS, Beltsville, Maryland 20705.

² Assistant Professor and Graduate Research Assistant, respectively, Department of Veterinary and Animal Sciences.