Changes in Type Ratings of Holstein Cows due to Age, Season, Stage of Lactation, Classifier, and Year

Abstract

Ratings of 233 Holstein cows, classified a total of 2272 times from 1945 to 1957 by official classifiers, were coded to maintain equal intervals (1.0) between ratings. Least squares analysis using dummy variables measured the effects of age with ratings grouped into lactations 1, 2, 3, 4, 5, 6+; season, spring or fall; stage of lactation, parturition to 60 days, 61-240 days, and 241 days to next parturition; and classifier, 1 through 13. Linear year effects were also measured. Analysis on a within-cow basis removed possible animal bias. Constants, calculated as partial regression coefficients, represented the additive effect of each environmental factor independent of all others. On a within-cow basis, coded over-all ratings decreased steadily with age, with a range of 0.92 between lactation 1 and 6+; spring ratings were higher than fall by 0.07; early- and late-lactation scores were higher (0.13 and 0.17) than mid-lactation. The range among classifiers was 1.38. Trends among subratings were similar except that feet and legs, and fore udder, showed smaller age and greater classifier effects; in late lactation, dairy character decreased (0.17) and body capacity increased (0.27). The linear decrease in over-all ratings was 0.03 per year, with a range of 0 to -0.06 for subratings.