Mastitis is considered among principal pathologies which strike dairy livestock and the bovines in particular, considering their economic and medical importance, it is significantly considered to highlight the parameters which play a role in the appearance of this pathology. Our study related to a sample of 500 milking cows, and during a whole year. These cows differed from age and breed point of view, but they lived under the same defective conditions of breeding from the habitat, hygiene and food point of view. The results of the study revealed that, Cows were infected for the period of stalling (winter and autumn), with a percentage of 26% and 22, 6% respectively, whereas for the period of the meadows (spring and summer) the infection was less frequent (15% and 17, 8%). Imported bovine milking breeds, showed a larger sensitivity towards mastitis i.e. Cross breeds: 15%; Pie noire race: 46, 6% and pie rouge race: 10, 4%. However, local breeds were more resistant compared to the others, with a rate of mastitis of only 9, 4%. Age did not have a direct influence on incidence of mastitis. Cows could be prone to the infection at any moment of their life, being given rigorous conditions of the Algerian breeding. Posterior udder quarters were more exposed to the infection, with 25, 84% and 25, 51% respectively for lefts to rights posteriors, whereas lefts and right anterior quarters have a percentage of 24, 32% each one. Present results showed that bacteriological quality of milk was very bad, following a bacterial contamination of collected milk, by Enterobacteria (100% of cases), Staphylococci (54% of cases), and Streptococci ones (13% of cases). Results of this study emphasized that the hygienic side does not have much consideration among stockbreeders, and consequently 50 to 80% of the herds suffer from mastitis.