| Popis: |
This study aimed to estimate the genetic parameters (heritability and genetic correlation), breeding value and genetic trends for some productive and reproductive traits of Holstein Friesian cows in Egypt with animal model statistical method. A total of 3400 lactation records collected from 1060 cow's progeny of 99 sires and 691 dams through the period from 1998 to 2010 were used in this study. Results of genetic correlations showed great variability from very high positive to very low negative values. High heritability estimates were recorded for all studied traits with the exception of days in milk, calving interval and days open which revealed low estimates. The ranges of cows breeding values have been found to be higher than either sires or dams for all studied traits. Genetic trends were positive for 305-day milk yield (2.68 kg), age at first calving (0.020), fat yield (0.031kg), fat% (0.001%) and protein % (0.002%), but were negative for protein yield (-0.098 kg) and days open (-0.219). In conclusion, higher range of the cow breeding values than either sires or dams revealed a wider genetic variation and a good opportunity for selecting the superior cows. Positive genetic trends for 305-day milk yield, age at first calving, fat%, fat yield and protein% indicated that there was a genetic improvement in these traits in desirable direction, but negative genetic trends for days open and protein yield indicating a decrease in mean breeding value for these traits over the study period. |
