Decline in milk production has. mostly been attributed to infectious agents that generally result in swelling of udder, changes in the constitutions of milk and finally induration of the udder which causing huge economic losses in livestock production. Mastitis is most important diseases of all the lactating animals. The most common Staphylococcus aureus which causes mastitis in cattle. Given the range of ill-effects of Staphylococcus aureus causing mammary infection in cows and buffaloes in Pakistan there is strong need for detection of strain involved. Likewise identification of clones with extensive geographic distribution wall provide insight into strain virulence and pathogenesis and also requiring public health intervention such as vaccination and antimicrobial restriction aimed at reducing the spread of the pathogen. In the present project the relatedness by elcctrophoretic profile of Staphylococcus aureus isolates involved in mastitis at dairy farns were studied, to compare the isolates of Staphylococcus aureus from different dairy farms. The samples from clinically/ subclinically affected at farms were collected, for isolation of Staphylococcus aureus, these samples were streaked onto Staph- 110 agar media plates and Staphylococcus aureus were be confirmed through biochemical and sugar fermentation tests. These conformed Staphylococcus aureus

Isolates were subjected to sodium dodecyl sulphate polycrylaniide gel electrophoresis. (SDS-PAGE) for electrophorctic protein profiling. The banding pattern of various isolates as against known molecular weight markers were recorded for interpretation of results.

It was concluded that protein profile is one of several methods for determining the relatedness or unrelatedness of bacterial strains. As immunization has been often attempted in efforts to control the mastitis, the diversity of Staphylococcus aureus strains and difficulties in vaccine development instruct that use of one or likely several strains in a herd or even in herds located in the same geographical region are recommended. Decision on representative strains can be made on basis of whole cell proteins, since such proteins of Staphylococcus aureus strain has already been shown, the isolates could be characterized by their total protein profiles and use of one or likely several strains of Staphylococcus aureus that are antigenically representative of the majority of the causative strains will overcome vaccine development difficulties.