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Sources of Variation Affecting Ratio Factors for Estimating Total Daily Milk Yield from Individual Milkings

Department of Animal Science, Cornell University, Ithaca, New York 14850

ABSTRACT

Morning and evening test-day milk weights were collected by Dairy Herd Improvement Association supervisors on all Dairy Herd Improvement Association herds in 16 New York counties from September, 1967, through September, 1968. There were 184,521 test-day records on 19,905 cows of five dairy breeds in 555 herds. Analysis of variance of the ratio of daily production to morning and evening production indicated herd production and age at calving were of no practical significance as sources of variation affecting multiplicative correction factors for single-milking testing schemes. Month of lactation, milking interval, and month of lactation by milking interval interaction were important. Adjustments for milking interval were the most important correction of individual milkings in a single-milking testing scheme. Multiplicative factors removed a larger part of the production effect than additive correction factors, thus reducing the effect of age and stage of lactation.