Objetivou-se com esta pesquisa, analisar e quantificar a influência do descarte involuntário de matrizes no impacto econômico da mastite em rebanhos leiteiros. A pesquisa foi realizada por meio de simulação no sistema computacional CUTOMASTITE,considerandorebanhosleiteiroscomtaxasdedescartede2,4e6TO MASTITE software, taking into account dairy herds with culling rates of 2, 4 and 6%. The expenditures on monitoring were considered as prevention (culture and ambiogram, bulk tank somatic cell count and individual somatic cell count) pre- and post-dipping, vaccination, treatment of dry cows and maintenance of milking machine. As curative measurements, the treatments of clinical cases (7% of the lactating cows) were considered. The impact of mastitis was estimated as being the total of losses plus expenses with prevention and treatment of clinical cases. The increase of culling rate influenced directly the economic impact of mastitis. The elevated economic impact stresses the need for monitoring the disease to decrease loss. The expenses on preventive treatment account a maximum 9.2% of the economic impact, which demonstrates the advantages of investing in that practice, which it will contribute significantly towards the decrease of the bulk tank somatic cell count and thus reducing the economic impact of mastitis