1,032,438 Jersey and 1,162,578 Holstein official Dairy Herd Improvement Association
(DHIA) records from 20,380 and 34,000 herd-years, respectively, were used to compute
herd-year means and within herd-year standard deviations for individual mature equivalent
(ME) milk, fat, and fat percent. These herd-year means and within standard deviations
were used to stratify records into five classes. Regressions for individual
daughter’s modified contemporary deviation (MCD) on sire’s predicted difference (PD)
were calculated for each class. The within herd-year standard deviations were also used
in some of the six different MCD calculations used to compute six different cow indexes
(CI) for each cow and trait. The six MCDs calculated were either the current deviation,
log adjusted deviation, or the deviation standardized to a constant variance in combination
with either the current correction for contemporaries merit or an adjusted correction.
The six different CI for each trait were compared by how accurately they
predicted the son's MCD trait and the daughter's MCD trait.
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