Relationship Between Days Open and Cumulative Milk Yield at Various Intervals from Parturition for High and Low Producing Cows

Abstract

Holstein lactation records from New York Dairy Records Processing Laboratory were used to estimate relationships between days open and cumulative milk yield at intervals from parturition and the effect of lactation number, season of freshening, and production on these relationships. The relationship of days open with total days in milk also was estimated. Quadratic regression equations that relate cumulative milk yield at 210, 240, 270, 300, 330, and 360 days from parturition and total number of days in milk with days open were estimated for cows with high and low yields in first, second, and third and later lactation freshening in three seasons. Milk yield early in lactation was used to classify cows in classes of high and low production. The association between days open and cumulative milk yield was less for cows within a production class than across all cows with production early in lactation ignored. The change in cumulative milk yield at 305 days associated with number of days open was greater for older cows than for cows in first lactation but not different between high and low producing cows within lactation. This indicates that correcting 305-day milk yield to a standard number of days open should be additive. Quantities of milk required to correct milk production to a standard 100 days open were calculated. © 1980, American Dairy Science Association. All rights reserved.