Phenotypic and Genetic Parameters Estimation for Growth Traits of Holstein Friesian x Boran Crossbred Dairy Cattle at Holetta Agricultural Research Center, Ethiopia Fikadu Wodajo1, 2 , Damitie Kebede1 and Mengistie Taye1 1Bahir Dar University, Colleges of Agriculture and Environmental Science, Bahir Dar, Ethiopia; 2 Ethiopia Institute of Agricultural Research, Holetta Agricultural Research Center, Holetta, Ethiopia This study was initiated to estimate phenotypic and genetic parameters for growth traits of Holstein Friesian x Boran crossbred dairy cattle at Holetta Agricultural Research Center (HARC) dairy farm. A total of 14,062 crossbred dairy calves performance records of 22 year (1997-2018) were used for the study. A General Linear Model (GLM) procedure of the Statistical Analysis System (SAS, version 9.0) was used to analyze the growth performance data and to determine the significance of fixed effects (year of birth, season of birth, dam parity (only for birth weight), sex of calf and calf genotype). The variance components and genetic parameters for growth traits were estimated by Average Information Restricted Maximum Likelihood (AI-REML) method, using the WOMBAT software fitting animal model. Four analysis models were fitted to optimize the model for each growth trait. The direct additive effect was included in all the models and it was the only random effect at the first model. In the 2nd and 3rd model, additive maternal effect and maternal permanent environmental effects, respectively, were fitted as 2nd random effect. The 4th model included both permanent environmental and additive maternal effects. The 2 rd and 4 th models were omitted the direct-maternal covariance. The log-likelihood ratio test was used for selecting the best fitted model. The overall least squares mean for birth weight (BW), weaning weight (WW), six months weight (SMW) and yearling weight (YW) were 28.5±0.11, 60.56±0.27, and 84.49±0.50 and 138.44±1.17 kg, respectively. The preweaning average daily weight gain (from birth to weaning) (PrWADG) and post-weaning average daily weight gain (from weaning to yearling) (PoWADG) were 359.61±2.72 and 279.94±3.60 g/day, respectively. Genotype, season of birth, year of birth, parity of dam and sex of calves were important sources of variation for most of the growth traits. Based on the log-likelihood ratio test, the 4th model for BW, 2nd model for WW, SMW and average daily weight gain from birth to weaning (PrWADG) and 1 st model for YW and ix average daily weight gain from weaning to yearling (PoWADG) traits were the best fitted. The estimates of direct heritability with its standard error from the best model of HF x Boran crossbred calves for growth traits were 0.15±0.04, 0.06±0.03, 0.07±0.04, 0.26±0.06, 0.05±0.03 and 0.28±0.05 for BW, WW, SMW, YW, PrWADG and PoWADG, respectively. The total heritability (h2 t) value for BW, WW, SMW, YW, PrWADG and PoWADG with best fitted model was 0.20, 0.12, 0.10, 0.26, 0.09 and 28, respectively. Among the growth traits, the highest direct genetic correlation was observed between YW and PoWADG (0.944±0.02) followed by WW and SMW (0.84±0.04). BW and WW (0.07±0.11) and BW and PrWADG (0.10±0.12) had a relatively lower genetic correlation. The genetic correlations among growth traits varied from 0.94±0.02 to 0.07±0.11 while the values of phenotypic correlation ranged from 0.93±0.04 to -0.03±0.04. The genetic trends were in progress up to weaning age but decline after weaning. The development of integrated management packages for different genetic groups of crossbred cattle are required to exploit the potentials of the dairy animals and the selection method of the herd must be based on the both phenotypic and genetic evaluation (breeding value) results or the selection criteria may need to revise). Keywords: Crossbred dairy cattle, genetic parameter, genetic trend, growth