Abstract:
The objective of this study was to estimate Daughte
r Yield Deviations (DYDs) of bulls
and Yield Deviations (YDs) for cows using a random
regression model and validation of
genetic trend using estimated
DYDs
and Method II of Interbull for test-day records of
Somatic Cell Score (SCS) in the first lactation of
Iranian Holsteins. Data
set included the
108995 test day records collected by the Animal Bre
eding Center of Iran from 2001 to
2010. Results of the present study indicated that v
ariation in
YDs
of cows at different
stages of lactation corresponds closely with their
Estimated Breeding Values (EBVs).
Because
YDs
and
DYDs
are considered as an additional measure of an anim
al’s genetic
merit, their correlation with
EBVs
is very important. The correlation between
DYDs
and
EBVs
of bulls for SCS was 0.88. High correlation estima
tes between
DYDs
and
EBVs
indicated that, in addition to EBV, the
DYD
can be an appropriate measure for dairy
cattle breeding programs. The correlation increased
with increase in the number of bull
daughters and the average number of test-days of da
ughters. Estimated
DYDs
for each
production year were used to validate the genetic t
rend obtained from the model which
was used for genetic evaluation. Results indicated
that genetic trend for SCS in the first
lactation of Iranian Holsteins was slightly overest
imated.
Keywords:
Dairy cow, Estimated breeding value, Genetic progre
ss, Mastitis, Validation of
genetic trend.
