Abstract:
This study was conducted to estimate the additive g
enetic components of calf mortality
in the first month of age, calving difficulty, and
birth weight in Holstein dairy cows in the
central regions of Iran. The records comprised 61,2
00 calves born between 1990 and 2011
from 60 dairy herds. Different threshold-linear mod
els in three groups of univariate,
bivariate, and multivariate models were used. The f
requency of calf mortality was 2.6%.
Distribution of calving difficulty score was 65.12%
in the first category (no assistance),
30.66% in the second, 3.12% in the third, and 1.1%
in the fourth (major assistance).
Averages of birth weight and dam age were 40.34 kg
and 769.4 days, respectively. Direct
Heritability estimation for calf mortality varied f
rom 0.005 to 0.027. The estimated
heritability for calving difficulty ranged from 0.0
32 to 0.050. Heritability for birth weight
was estimated about 0.22. The results of this study
showed that there were genetic
variations for all traits. Although there was no st
rong additive genetic correlation between
the traits, an environmental correlation between mo
rtality and other traits was observed.
Results suggested that implementation of threshold
models for mortality trait was more
favorable, but they were not reflected in genetic a
nalysis of calving difficulty records.
Furthermore, current findings indicated that benefi
t from the use of multi-traits models
for genetic evaluation of postnatal mortality depen
ded on the methodology (linear or
threshold model) used for mortality trait.
Keywords
: Birth weight, Calf mortality, Calving difficulty,
Genetic parameters, Linear-
Threshold models.
