In this study, four broiler parent flocks have been followed from the onset of the production period (week 20) until slaughter (week 60). Every week, approximately ten dead broiler breeders, randomly selected among birds dead on their own, were collected and subjected to a full post mortem analysis including bacteriological examination. In total 997 breeders were investigated and for the first time Staphylococcus agnetis was isolated in pure culture from cases of endocarditis and septicemia from 16 broiler breeders. In addition, the cloacal flora from newly hatched chickens originating from the same four flocks were characterized and S. agnetis was found in pure culture of several newly hatched chickens (n = 12) and only in one case in combination with another species. Clonality of the isolates was examined by pulsed-field-gel-electrophoresis which showed indistinguishable patterns in isolates from both broiler breeders and broilers. Three isolates were whole genome sequenced to obtain knowledge on virulence genes. The isolates harbored a number of genes encoding different fibrinogen binding proteins and toxins which might be important for virulence. The present findings demonstrate that S. agnetis may be associated with mortality in broiler breeders. No disease was associated with the broilers which were found positive for S. agnetis in the cloaca.