Microbiological Evaluation of Milk Quality and Antibiogram in Dairy Cows Managed on Pasture

Mastitis is a disease in dairy cattle that damage the milk chain. It was aimed identify the major causative agents of bovine mastitis in small dairy farms by producing an antibiogram and analysis of milk quality. Methods- During the summer, 280 dairy cows were examined on a farm located in Camapuã, MS, Brazil. The farm had a concrete milking facility and used cleaning and disinfection of the udder before and after milking to control mastitis. For assess microbial resistance, two samples of milk per cow were collected biweekly between January and March. The antibiotics sulfazotrim (25 μg), penicillin (10 μg), streptomycin (10 μg), vancomycin (30 μg), chloramphenicol (30 μg), tetracycline (30 μg), amoxicillin (10 μg), and gentamycin (10 μg) were used. Results- A total of 17.14% of the animals were positive for the California Mastitis Test (CMT). The identification of the pathogens revealed that Staphylococcus aureus accounted for 41.65% of the isolated organisms and Escherichia coli for 37.5%. Our results showed only sulfazotrim and chloramphenicol had effective results for both Gram-negative and Gram-positive bacteria. The isolated strains presented high resistance to the other tested antibiotics. Conclusions- sulfazotrim (25 μg) and chloramphenicol (30 μg) can be used to disinfect the udder of dairy cows.Â