Genetic evaluation of dairy cows in Tehran province based on 305-d milk records in first and second lactations

The main objective of this research was genetic evaluation of dairy cows in Tehran province for 305-d milk production trait based upon 1- first lactation records (scenario one, S1) and 2- first and second lactation records (scenario two, S2). A total of 206,013 records (126,600 first lactation records and 79,413 first and second lactation records) belonging to 126,600 head (representing 2,876 sires and 89,368 dams) in 260 herds was used. The cows calved between 1983 and 2011. Total number of animals in the pedigree file was 218,844 head. DMU software was utilised for estimation variance components (REML) and for prediction breeding value (BLUP). Genetic trends for scenarios 1 and 2 were 16.6 kg (SE=2.42 kg) and 14.9 kg (SE=2.42 kg) per year, respectively and non-significance difference was found between them. Heritability of the trait was 0.281 and 0.247 for these scenarios, respectively. Based on the type of used records, mean accuracy selection of the daughters (0.67 for S1 and 0.69 for S2) were significantly (P<0.0001) different from each other. The findings of the present study revealed that more or less similar genetic trend as well as selection accuracy could be obtained as the genetic evaluation of the cows is undertaken through the scenarios, suggesting that first lactation record could be used to decrease generation interval, and as a consequence, to increase annual genetic gain.