A comparison of different selection indexes for some economic traits in Holstein Friesian cows

The genetic as well as phenotypic parameters for 10-month milk total (10 MMY), lactation length (LL), and age at first calving (AFC) were calculated with data from 1863 first lactation records of Holstein Friesian cows imported from Germany and managed at a private farm in Egypt between 2002 and 2012. Multiple Trait Derivative Free Restricted Maximum Likelihood was used for the data analysis (MTDFREML, Boldman et al., 1995). Means of 10 MMY, LL and AFC were 9710 kg, 357 days, and 27.17 months, respectively. All the traits examined were significantly impacted by the calving season and year.  Heritability estimates for 10 MMY, LL and AFC were 0.37±05, 0.20±0.01 and 0.05±.002, respectively. Four selection indices were calculated by using three different methods of economic values, (1) actual relative economic weight, (2) one phenotypic standard deviation and (3) one genetic standard deviation.       Comparison of the three methods for estimating relative economic values revealed no differences in any of the three methods for the expected genetic gain per generation for each trait, the correlation between the total genetic value and the index, or the effectiveness of various indices in comparison to the original index (I₁). Therefore, the three methods were succeeded in predicting the genetic gain per generation for the three traits studied. However, the second method (one phenotypic standard deviation) was recommended based on ease of calculation.