Minimum days dry to maximize milk yield in subsequent lactation

Overview & Synopsis

The objective of this research was to determine the effect of days dry (DD) on actual milk yield and to identify the minimum dry period length needed to maximize milk yield in the subsequent lactation. Field data collected through the U.S. dairy herd improvement association from January, 1997 to December, 2003 and extracted from the Animal Improvement Programs Laboratory national database were used for analysis. Actual lactation records calculated from test-day yields using the test-interval method were used in this study. The model for analysis included herd-year of calving, year-state-month of calving, previous lactation milk yield, age at calving, and DD as a categorical variable. Interactions were added to this model to determine if the effects of DD on subsequent lactation milk yield depended on previous lactation milk yield, age at calving, somatic cell score, or days open. Milk yield in the subsequent lactations was generally maximized with a 60 to 65 d dry period, regardless of parity. Days dry effects on milk yield were, for the most part, consistent across lactations, although dry periods < 35 d are somewhat more detrimental to milk yield after first lactation than after second and later lactations. Dry periods less than 20 d result in very pronounced losses in subsequent lactation yield. A short dry period (< 40 d) for high producing cows that bred back early in lactation proved to be the worst combination in terms of maximizing subsequent lactation milk yield.