Comparative Accuracy of the Plastic Bead Method of Golding and the Lactometer Method of Watson for Routine Determination of Solids-not-fat in Milk

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Abstract
The plastic bead method of Golding was evaluated as a rapid test for solids-not-fat (SNF) in the milk of individual cows. Ten plastic beads each varying 1 mg in density in the range of 1.025 to 1.034 are placed in a 4-oz. sample jar fitted with a plastic grid and a metal screw-cap. Milk is sampled directly into the sample jar and after the fat has been liquefied by heating to 104[degree] F and holding for 5 min., the test is made by counting the number of sinking beads at 68[degree] F. A formula for converting the number of sinking beads to percentage SNF was calculated, using 1,873 milk samples from Guernsey, Holstein, and Jersey cows of 53 herds. This formula is: per cent SNF = 9.13 - 0.279 B + 0.307% F where B is the number of plastic beads sinking at 68[degree] F and per cent F is the percentage fat in the milk. In a 2nd experiment, plastic beads and the lactometer of Watson were compared, using gravimetric assays for reference. On 300 milk samples from 6 breeds the standard deviation from regression was 0.17% SNF for the lactometer and 0.18% SNF for the plastic beads. The plastic bead method is sufficiently accurate for the routine testing of milk of individual cows for per cent SNF. The method is simple and rapid and requires no more milk than is routinely sampled for Dairy Herd Improvement Association testing.