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Factor Analysis for Evaluating Relationships between First Lactation Type Scores and Production Data of Holstein Dairy Cows¹

Animal Science Department, Statistics Department, Iowa State University, Ames 50011

ABSTRACT

Data on linear type scores for 18 traits from evaluations from Twenty-First Century Genetics from September 1979 to December 1983 were matched against the DHIA production records. Data for production were 43,428 records by 228 sires, each with at least 20 progeny in at least nine herds. Data were randomly split to analyze and validate the investigation of factor analyses to relate type scores and production. Type scores (1 to 50 points) were adjusted for days in milk and age at first calving. Means of the adjusted type scores ranged from 25.2 to 31.7 (± 5.39 to 9.09 SD). A principal component analysis showed that the first eight components accounted for more than 69% of the total variance in type scores. A principal factor analysis followed by a factor rotation was used to define new factors. Multiple linear regression on these factors indicated that herdmate deviation milk and fat are more closely related to characteristics of the mammary system than they are to body traits. For herdlife analyses, using 17,288 records, cows with well-attached udders stayed in herds longer.

¹ Journal Paper Number J-12359 of the Iowa Agriculture and Home Economics Experiment Station, Ames; Project Number 1053.