Phenotypic and Genetic Parameters Estimation for Reproductive and Milk Production Traits of Pure Jersey Breed at Adea-Berga Dairy Research Center, Central Highland of Ethiopia Nibo Beneberu 1, 2*, Kefyalew Alemayehu1, Wossenie Shibabaw1 and Kefale Getahun2 1Bahir Dar University, Colleges of Agriculture and Environmental Sciences, Bahir Dar, Ethiopia; 2Holeta Agricultural Research Center, Holeta, Ethiopia Performance evaluation and estimates of genetic parameters for economically important traits are the bases for genetic evaluation, planning breeding program and selection for dairy cows. This study was aimed to estimate phenotypic and genetic parameters for reproductive and milk production traits of pure Jersey dairy cows at Adea-Berga Dairy research center. The data collected from 1986 to 2019 from a herd maintained at Adea-Berga dairy Research Center was used to estimate performance and genetic parameter estimates for reproductive traits (age at first service (AFS), age at first calving (AFC), calving interval (CI), days open (DO) and the number of services per conception (NSPC)), and milk production traits (lactation milk yield (LMY), daily milk yield (DMY) and lactation length (LL)). A general linear model procedure of the Statistical Analysis System (SAS, version 9.0) was used to analyse the reproductive and milk performance data. The genetic parameters and breeding values for reproductive and milk production traits were estimated using WOMBAT software (Meyer, 2012). Univariate analysis was undertaken for each trait for estimation of heritability, repeatability and breeding values, whereas genetic and phenotypic correlations were estimated using bivariate analysis. The result of fixed-effect analysis revealed that the influence of year caused significant (p<0.0001) variation in all reproductive and milk production traits. NSPC, LMY, DMY and LL were significantly influenced by parity (P<0.0001). CI and DO were significantly influenced by animal group (P<0.0001). The overall least squares mean (LSM±SE) for AFS, AFC, CI, DO, NSPC, LMY, DMY and LL were 22.93±0.22 months, 32.95±0.22 months, 494.16±3.68 days, 221.09±3.73 days, 1.99±0.03, 2166.10±26.71 Litres, 6.37±0.05 Litres and 344.89±3.81 days, respectively. The estimates of direct heritability (h2a) with their standard errors for AFS, AFC, CI, DO and NSPC were 0.05±0.08, 0.05±0.05, 0.03±0.02, 0.04±0.02 and 0.001±0.02, respectively. The direct heritability estimates for LMY, DMY xv and LL of pure Jersey cattle were 0.14, 0.12±0.04 and 0.04±0.02, respectively. Low direct heritability estimates for the reproductive and milk production trait in this study indicates that improvements of the traits are possible through management than through genetic selection. The repeatability of CI, DO, NSPC, LMY, DMY and LL were 0.09±0.02, 0.08±0.02, 0.05±0.02, 0.33, 0.40±0.02 and 0.10±0.02, respectively. The genetic correlations between reproductive traits were varied from -0.10 to 1.00±0.11 while the values of phenotypic correlation were found ranging from 0.03±0.04 to 0.98±0.002. For milk production traits, the genetic correlations varied from 0.93±0.22 to 0.98±0.07 while the values of phenotypic correlation were found ranging from -0.03±0.02 to 0.82±0.01. The direct genetic correlations between reproductive and milk production traits were varied from -0.89 to 1.00 while the values of phenotypic correlation ranged from -0.003±0.04 to 0.46±0.02. The positive direct genetic correlations among traits in the present study indicated that selection of one trait might improve the other trait. The average breeding values for AFS, AFC, CI, DO, NSPC, LMY, DMY and LL were -0.00948 months, 0.02269 months, -1.13339 days, -3.00389 days, -0.00021, 26.89 Litres, 0.07 Litres and 0.09 days, respectively. The negative breeding values for reproductive traits tend to be associated with below average performance. The negative trend for milk production traits implies non-efficient breeding programs, inefficiency in selection based on phenotypic performance, absence of proper culling of unproductive cows, environmental stresses and management practices. In conclusion, the results of this thesis suggest that the improvement of reproductive and milk production traits of the pure Jersey cattle population at Adea-Berga Dairy Research Center is possible through improving the level of feeding, breeding and health management than through genetic selection. Keywords: Breeding value, genetic parameters, genetic trend, production traits, pure Jersey cows, reproductive traits