Study of longevity in Iranian Holstein dairy cows using random regression model

Abstract

Introduction: The longevity in dairy cow is the duration of presence of an animal the herd
from the date of first calving to the date culled. In present research, the aim is
1) to estimate the genetic parameters of the longevity trait of uncensored animals using
random regression model and 2) to study longevity of daughters of sires in the population
using the EBV of bulls based on 20 daughters and 3) to test the random regression model
(RRM) for EBV prediction of Animals with censored data.
Materials & methods: Genetic parameters of longevity and breeding value of bulls were
estimated by ECHIDNA software using RRM with restricted maximum likelihood (REML)
method. The file used for the genetic evaluation contained data on 18,120 daughters from
906 bulls. A number of 20 daughters that randomly selected from each sire to use for EBV
prediction. In addition to the daughters used for genetic evaluation (18,120 cows), there
were 285,064 daughters of the bulls in the main file. The bulls were grouped according to
the Breeding value from high to low based on the area under the normal curve. Then, the
mean of longevity of the daughters in each group who were not used the EBV prediction
calculated. In a file 10 daughters were randomly selected of 20 daughters of each bull and
their months of longevity divided by 2 and 3. These data were considered as censored in the
data file.
Results: The permanent environmental effect and the additive genetic effect had the largest
and smallest contribution to the total variance, respectively. The heritability of the trait was
low (0.003-0.032) which is in agreement with results of other report. The difference of
mean longevity between groups (LSD test) was significant (P˂0.01). Also, the increase of
the mean of EBV of the groups, the mean of longevity of their daughters in the population
increased. The correlation of EBV of animals with censored and uncensored data state were
+0.815 .
Discussion: In the split the low heritability of the longevity trait, using the sperm of
superior bulls in terms of EBV of longevity can improve the longevity in the population.
Also, it is possible to evaluate and select the bulls with a low progeny number and increase
the mean of longevity in the population of Holstein dairy cows. Moreover, the EBV of
longevity for young and producing animals can be predicted by RRM.