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A Comparison of Detergent Tests for Butterfat in Milk with Official Methods

Dairy Products Section, Eastern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture, Washington, D. C.

W. R. Harvey

Biometrical Services, Agricultural Research Service, U. S. Department of Agriculture, Beltsvile, Maryland¹

ABSTRACT

A collaborative comparison of the Schain and Dairy Products Section (DPS) tests with the official methods, the Babcock and Mojonnier tests, was performed by a group of experienced research workers. The volumetric tests were performed in duplicate by eight men; the Mojonnier test in quadruplicate by one man. Twelve cows, comprising four breeds with three cows of each breed, were used. Morning and evening milk was analyzed one day of the first, third, and fifth week.

The Babcock test has a closer correlation with the Mojonnier test than does either the Schain or the DPS test. The Schain test correlation is .9889, the DPS .9886, and the Babcock .9963, whereas a perfect correlation is 1.000.

The three volumetric tests averaged slightly higher than the Mojonnier: the Schain test 0.11% butterfat, the DPS 0.06%, and the Babcock 0.09%.

The standard deviation between testers was 0.15%, 0.18%, and 0.10% for the Schain, DPS, and Babcock tests, respectively. Therefore, the tester is a significant variable in these tests.

The butterfat content of the milk from these individual cows varied considerably, up and down, over the 5-wk. period. Differences of 1% fat were found in five out of the 12 cows, using the average of the morning and evening samples. This variation is far greater than that attributable to the analytical procedures or to the individual testers.

¹ In collaboration with R. Bassette, M. Keeney, J. F. Mattick, and H A. Newlander (present address: Meadow Gold Products Co., Washington, D. C.), Dairy Husbandry Department, University of Maryland, College Park, Maryland; F. M. Grant and R. Trimble (retired), Animal Husbandry Research Division, Agricultural Research Service, USDA, Beltsville, Maryland; E. M. Parrish, Department of Public Health, District of Columbia, Washington, D. C., and H. E. Vettel, Eastern Utilization Research and Development Division, Agricultural Research Service, USDA, Washington, D. C.