Effects of Season, Age, and Stage of Lactation upon Type Ratings of Holstein Cows

Abstract

Spring and fall type ratings by official inspectors from 1945 to 1957 were coded to maintain equal intervals (1.0) between ratings. Lactation numbers represented age with scores grouped into 1st, 2d, and 3d through 5th (mature) lactation. Each lactation was divided (a) parturition to 60 days, (b) 61 to 240 days, and (c) 241 days to next parturition. Only cows with 5 or more ratings were included. Least squares analyses using dummy variables measured the various environmental effects independent of each other on 918 ratings of 113 cows. With confounding of the other measured effects removed, and using coded values, over-all ratings in fall were lower than those in spring by 0.09 (P<0.08): 1st and 2d lactation scores were lower than mature scores by 0.52 and 0.29 (P<0.01), respectively. Early and mid-lactation scores were similar, but late-lactation scores were 0.15 lower (P<0.01). Subratings for fall, and for 1st and 2d lactation, generally were lower than their counterparts. Scores in late lactation were higher, except for dairy character which scored 0.19 lower (P<0.01) than in mid-lactation. Application of adjustment factors increased repeatability only slightly. Adjustments for the significant influences in studies with limited numbers of observations per cow would yield more accurate type estimates.