1PL = productive life (days from first calving to culling); S1, S2, and S3 = survival through lactations 1, 2, and 3, respectively (survival = 1 if the cow survived that lactation; = 0 if the cow was culled during that lactation;= missing if the cow died before that lactation); FS = fertility-determined survival (1 = cow was not culled due to fertility; 0 = cow was culled due to fertility); UHS = udder heath-determined survival (1 = cow was not culled due to udder health; 0 = cow was culled due to udder health).