An "Arkray Brucella Abortus Antigen" is a diagnostic reagent for detecting Brucella antibodies in animal or human serum, used in rapid agglutination slide tests such as the Rose Bengal Test. It consists of killed, stained Brucella abortus bacteria that react with specific antibodies, forming visible clumps (agglutination), which helps in diagnosing brucellosis, a zoonotic disease affecting cattle.