Epidemiological analysis of an outbreak of bovine mastitis in a dairy herd in the state of Rio Grande do Sul

Bovine mastitis is an infectious disease that causes economic losses in dairy herds due to impaired milk production and milk quality and costs with both culling and treatment. The objective of the study was to analyze an outbreak of bovine mastitis in a large dairy herd in the state of Rio Grande do Sul. The herd with 405 lactating cows showed an increased incidence of clinical mastitis characterized primary by clots in the milk. California Mastitis Test (CMT) was performed in all milking cows and milk samples were collected from those presenting 2+ or 3+ based on the viscosity of the gel; 33.5% of the lactating cows presented 2+ or 3+ in the CMT test. Staphylococcus aureus and Streptococcus agalactiae were obtained from 33% of milk samples. The odds of a cow showing mastitis according to CMT criteria increased with the increment of average milk production (p = 0.00765); the risk of a cow with contagious mastitis increased with the lactating period (p = 0,042). It could be concluded through the epidemiological analysis that the outbreak has started after the introduction of new animals into the herd.