Date of this Version
Dairy cattle type appraisal data were examined to determine whether body and udder conformation and management ratings were affected by age and period of lactation at appraisal. Data were collected from 1961 to 1968 from 188 herds having over 23,000 Holstein type appraisals. The body and udder traits were scored by scheduled appraisers, and the management traits were coded by each dairyman. Some of the 35 original traits were composed of more than one descriptive characteristic and, as a result, 49 renamed traits were derived from these.
A model was selected that considered years and herds as well as cow effects to reduce bias in the estimates of age x stage-of-lactation differences that would result frcm culling cows on type score. Age differences were large for about one-third of the traits, especially for mastitis, body weight, and depth of udder. In general, differences from stage-of-lactation were not as large as from age; nevertheless, trends were evident for several traits. Interactions between age and stage-of-lactation were relatively small.