PRINCIPAL COMPONENT ANALYSIS OF GENETIC BREEDING VALUES FOR MILK AND REPRODUCTIVE TRAITS IN FRIESIAN CATTLE IN EGYPT

The aim of this study was to assess genetic parameters and breeding values for milktraits (total milk yield, TMY and lactation period, LP) as well as reproductive traits, including daysopen (DO), calving interval (CI) and age at first calving (AFC) in Friesian cattle. The study alsoinvolved analyzing the relationship between genetic breeding values using principal componentanalysis (PC) and constructing a selection index to improve overall performance. A dataset comprising2837 records from 1243 cows, offspring of 108 sires and 835 dams during the period from 2000 to2015 was collected from two experimental stations, Sakha and El-Karada, managed by the AnimalProduction Research Institute. The estimated heritability values were 0.29, 0.23, 0.04, 0.06, and 0.07for TMY, LP, CI, DO, and AFC, respectively. Repeatability estimates stood at 0.30 for TMY, 0.27 forLP, 0.04 for CI, and 0.12 for DO. Among four principal components, two exhibited eigenvaluesgreater 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 wereformulated as follows: PCs1=0.361EBVTMY+0.446EBVLP +0.490EBVAFC+0.475EBVCI+0.453EBVDOPCs2=0.643EBVTMY+0.494EBVLP -0.178EBVAFC-0.421EBVCI-0.365EBVDO. In conclusion, PC couldbe 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 thegenetic index represented by PC2, suggesting its potential use in selection programs to enhance milktraits while concurrently reducing CI, DO, and AFC.