GENETIC EVALUATION OF SOME PRODUCTIVE LIFETIME TRAITS OF LOCALLY BORN FRIESIAN COWS IN EGYPT

Data on 2186 lactation records of 541 pure Friesian cows presenting 43 sires and 372 dams born at the Dairy Unit of Milk and Meat Project of the Faculty of Agriculture, Alexandria University, between 1983-2006 were utilized to evaluate lifetime milk yield (LMY), days in lactation (LDL), daily milk yield (LDMY) and number of lactations (NL) of Friesian cows. Also, the effects of season and year of calving and age at first calving on the previous traits were studied. The least square means of LMY, LDL, LDMY and NL were 18310 kg, 1318 day, 13.6 kg and 4.04 lactations, respectively. Season of calving had no significant effect on all studied traits. Year of calving had significant effect (P<0.01) on all studied traits. Age at first calving had significant effect (P<0.05) on LDMY, but had no significant effect on LMY, LDL and NL. The heritability estimates from univariate animal models were 0.272, 0.137, 0.117, and 0.116 for LMY, LDL, LDMY and NL, respectively. The moderate heritability for LMY emphasized the possibility of realizing a considerable rate of genetic improvement in this trait through selection programme. The genetic corrletions estimated from bivariate animal models were positive ranging from 0.264 to 0.993, except that between LMY and LDMYwas negative (-0.163). All correlations among all traits were significant (P<0.01). The positive genetic correlations between LMY and each of LDL and NL indicate that selection for any traits associated with genetic improvement in other traits. Phenotypic correlations among all traits were positive ranging from 0.099 to 0.966 and significant (P<0.01 or P<0.05). The breeding values for LMY, LDL, LDMY and NL of cows ranged between -759 and 1139 kg, -101 and 105 day, -1.77 and 1.82 kg and between -01.64 and 2.69 lactations, respectively, the corresponding values for dams were between -814 and 1107 kg, -122 and 100 day, -2.38 and 1.53 kg and between -1.74 and 3.24 lactations, respectively. The breeding values for sires were between -560 and 748 kg, -117 and 83 day, -1.79 and 1.26 kg and between -1.44 and 3.12 lactations for the respective traits. The genetic trends estimated by the regression of sires breeding values on time were positive and nonsignificant for LMY, LDL and NL and negative approached zero for LDMY. Generally, the results indicate that improvement of productive lifetime traits of Friesian cows could be obtained through both selection programme and improvement of management conditions.