Abstract
Different dairy cattle breeds in Egypt that notes deviation in milk composition and daily milk production which related to diversity in genetic character. To study the diversity between three main breeds (Native, Holstein and brown Swiss) in Egypt based on genetic polymorphism and biochemical investigation. In order to study the polymorphism of performance genes as (GH and PRL), the PCR-RFLP method was performed. A 428bp and 156pb fragments of GH and PRL genes respectively were amplified via PCR. These fragments were then restricted with the enzymes Alu1and RsaI respectively. In this study present two alleles,V and L in GH and A, B in PRL. L allele for GH and A allele for PRL are predominant and higher polymorphic in Holstein breed than Brown Swiss and Baladi breed. Hormonal assay for GH and PRL were measured in high and low producers in three breeds of cattle under study which give highly average level in high and low producers Holstein breed when compared to Brown Swiss and Baladi breeds, and this indicated when measured daily milk yield in high and low producers Holstein breed highly yield when compared to other breeds. Inversely expected for milk constituent (protein, fat, lactose, ash and total solid) high level were measured in low and high producers Baladi breed when compared two other breeds. This concluded that there was significance difference in some performance genes (GH, PRL) in genetic polymorphism and biochemical deviation in three breeds, the best one for milk production is Holstein breed than other two breeds.

Key words: Cattle, GH gene polymorphism, PCR-RFLP, Hormonal assay, Milk composition