Variation in Mastitis Screening Tests and Milk Composition of Udder Quarters under Normal Conditions and Following Omission of a Milking

Abstract

The sources of normal variation in milk composition and mastitis screening tests were studied on 384 quarter samples from 48 cows. Most of the variation in milk composition could be accounted for by differences among cows and day-by-cow interaction (day×cow). The major sources of variation in mastitis screening tests were among quarters within cows (quarters/cows) and cows.With the effect of trials, days, cows, day×cow, and quarters/cows removed, significant correlations were obtained between chloride and lactose (−.453), chloride and leucocytes (.415), and catalase and leucocytes (.577).Calculated losses in milk production of quarters with California Mastitis Test (CMT) scores of 1, 2, and 3, compared to opposite negative quarters, were .41, .65, and 1.48lb per quarter per milking, respectively. Comparable decreases in SNF percentage were .10, .15, and .40.Omitting a milking resulted in an increase in CMT, catalase, leucocytes, and chloride, and a decrease in SNF, milk production, and lactose. The degree of reaction to the CMT before omitting a milking did not affect the magnitude of these changes.