Variation in Cow Evaluation From Records in Progress

Abstract

Records in progress from 187,281 first-lactation Holstein cows were compared with later in-progress and complete records. Correlations between projected milk yield from records in progress and 305-day records increased from .80 for 40 to 69 days in milk to .99 for 280 to 304 days in milk. Corresponding average absolute differences decreased from 777 to 68kg. Correlations involving cow index for milk increased from .91 to .99. Analysis of variance of change from projected records in progress to 305-day yield of milk and fat for 93,727 cows showed regions, herds within regions, year-month of calving, age, and linear and quadratic regressions on days in milk were highly significant effects. Herds within regions were not significant when the change involved records deviated from yield of modified contemporaries. Although a similar analysis of change in cow index resulted in significance for those effects, differences among regions, months, or ages were less than 18kg and not of practical importance. In these data from first-lactation Holsteins, current projection factors underestimated 305-day milk yield by about 300kg at mid-lactation and appeared to underestimate a high percentage of all records in progress.