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This study was conducted to detect the most appropriate model that fits data of birth weight (BW) and weaning weight (WW) traits of Friesian calves. Body weights of 1371 calves over a 22 years and WW of 678 Friesian calves over a 19 years from a herd of Friesian in Gemmaza Ministry of Agriculture, Egypt were used. The fixed effects included in the model were parity, season, sex, year of calving in addition to the random effects to estimate direct and maternal heritability's, permanent maternal environmental and error. The parameters were estimated by using Variance Component Estimation (MTDFREML) programs. Six different animal models were fitted for the traits ranging from a simple to the most comprehensive model, were used to compare them. The overall means were 30.4 kg and 85.1 Kg, for BW and WW, respectively. Non-genetic factors (fixed effects) had highly significant (P<0.001) effects on BW and WW of calves. Estimates of direct heritability were moderate, they ranged from 0.28to 0.30 for BW and from 0.18 to 0.28 for WW. Maternal heritability was relatively low for both BW and WW, ranging from 0.06 to 0.08 for BW and was 0.04 for WW. Permanent environmental effect Pe in the 2 model was relatively higher than that of other models, while inclusion of maternal genetic effects (Models 3-6) showed further reduction in ha for which there was negligible difference in ha of the other models within each trait. Akaike Information Criterion (AIC) was used to determine the most appropriate model for the studied traits. Model 5 : Y =Xb+Z1a+Z2c+ Z3m + e Cov (a, m)= 0 A σ am was the most appropriate model for BW, while, Model 4 : Y =Xb+Z1a+Z3m+e Cov (a, m)= A σ am was the most appropriate model for WW trait. The higher range of calves breeding values compared with those of sire or dams means that selection for BW for calves is leading to an increase in WW for the next generation.

ESTIMATION OF GENETIC PARAMETERS FOR GROWTH TRAITS USING DIFFERENT MODELS FOR FRIESIAN CATTLE RAISED IN EGYPT