Study of Longevity in Iranian Holstein dairy cows using Random Regression Model

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. 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. 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. 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.