The aim of this study was to assess genetic parameters and breeding values for milk
traits (total milk yield, TMY and lactation period, LP) as well as reproductive traits, including days
open (DO), calving interval (CI) and age at first calving (AFC) in Friesian cattle. The study also
involved analyzing the relationship between genetic breeding values using principal component
analysis (PC) and constructing a selection index to improve overall performance. A dataset comprising
2837 records from 1243 cows, offspring of 108 sires and 835 dams during the period from 2000 to
2015 was collected from two experimental stations, Sakha and El-Karada, managed by the Animal
Production Research Institute. The estimated heritability values were 0.29, 0.23, 0.04, 0.06, and 0.07
for TMY, LP, CI, DO, and AFC, respectively. Repeatability estimates stood at 0.30 for TMY, 0.27 for
LP, 0.04 for CI, and 0.12 for DO. Among four principal components, two exhibited eigenvalues
greater than 1, collectively explaining 94.05% of total variance. PC1 and PC2 accounted for 67.87%
and 26.18% of the variance, respectively. Genetic index equations derived from these two PCs were
formulated as follows: PCs1=0.361EBVTMY+0.446EBVLP +0.490EBVAFC+0.475EBVCI+0.453EBVDO
PCs2=0.643EBVTMY+0.494EBVLP -0.178EBVAFC-0.421EBVCI-0.365EBVDO. In conclusion, PC could
be utilized in genetic improvements of economic traits instead of traditional selection programs.
Notably, a favorable correlation between milk production and reproductive traits was observed in the
genetic index represented by PC2, suggesting its potential use in selection programs to enhance milk
traits while concurrently reducing CI, DO, and AFC.