Crossbreeding effects on milk and fat yields performance of Iran population local cattle

In this study، the effect of crossbreeding were studied on local cattle performance، using information Holstein and Brown Swiss crossbred cows collected from 1993 to 2003 by Animal Breeding Center of Iran (ABCI). Milk and fat yield traits were considered in this research The data were analysed by least squres method with a modle that includded fixed effects of years and season of birth، genetic groups، lactation and region. Statistical analysis using least squares methods showed significant effects of genetic groups، lactation، region، year and season of birth on milk and fat yield in crossbred cattle (p<0. 001). The average milk and fat yield were 1599. 15±90. 52 and 1989. 54±110. 15 and 2148. 94±91. 81kg 60. 71±3. 34 kg، and 82. 26±4. 59kg and 85. 27±3. 42 kg for local and Brown Swiss × Local and Holstein × Local crossbred cows، respectively. The highest values for both traits were for the cows having 87. 5% Holstein and 62. 5% Brown Swiss inheritance and lowest values for those having 12. 5% exotic inheritance. Esimates of breed and individual heterosis effects carried out with Weight Least Square method. These effects for Holstein × Local crossbred were 20. 9 and 15. 32 kg for milk yield، 867 and 651 gr for fat yield. It was cocluded that the productive potential of local cattle can be increased by using exotic semen of genetically superior sires، through intensive management and with effective disease control programme.