Animal Science Department
Title
Multiple Trait Evaluation of Bulls for Calving Ease
Document Type
Article
Date of this Version
February 1984
Abstract
Evaluation of bulls for calving difficulty
of their calves by a multiple trait, mixed
model procedure seems appropriate for a
number of reasons. Average calving ease
scores and their variances and heritabilities
differ according to sex of calf and parity
of mother. The multiple trait procedure
automatically accounts for differences in
averages, variances, and heritabilities. The
procedure also allows for the magnitude
of herd-year-season effects to be different
for four traits as defined by calving
difficulty scores when measured on: male
birth by a heifer, female birth by a heifer,
male birth by a cow, and female birth by
a cow. Covariances among herd effects
for the four traits are used in the multiple
trait procedure to prevent certain comparisons
within herd from being lost.
Records on all four traits are weighted
properly to evaluate sires for calving ease
for all sex-of-calf and parity-of-cow
combinations. Evaluations for the four
traits can be weighted to obtain a single
evaluation for expected fraction of
acceptable births.
Computing costs do not seem prohibitive.
The procedure, however, does
not take advantage of ordering of categorical
responses or of an underlying
continuous biological distribution as
would threshold models.
Download
Comments
Published in J Dairy Sci 1984, 67:3025-3033. Copyright © 1984 The American Dairy Science Association. Used by permission.