Juliana FM Mendonça, Maria AVP Brito, Carla C Lange, Márcio R Silva, João B Ribeiro, Letícia C Mendonça and Guilherme N Souza
The aim of this study was to evaluate the reduction of intramammary infection caused by Streptococcus agalactiae and Staphylococcus aureus in a Holstein dairy herd under tropical conditions. The period of study was from January 2012 from January 2013 in a dairy herd composed by Holstein cows, with an average of 142 lactating cows/month. Milk samples were collected from individual lactating cows for microbiological tests. The sampling lactating cows was in order to identify those infected by Streptococcus agalactiae for the treatment of all mammary quarters with intramammary antibiotics, as well as to identify chronically infected lactating cows by S. aureus for possible culling. During this period, 161 treatments of cows with an intramammary antibiotic were performed to eliminate Streptococcus agalactiae, and nine cows chronically infected with Staphylococcus aureus were culled. The percentages of infected cows with S. agalactiae in January 2012 and January 2013 were 61.6% and 2.2%, respectively. For the same months, the percentages of cows infected with S. aureus were 28.3% and 19.4%, respectively. The intramammary antibiotic treatment of lactating cows was efficient in eliminating infection caused by S. agalactiae and consequently the prevalence of infected animals in the herd. The reduction in S. aureus prevalence among cows was associated with the culling of cows chronically infected by this pathogen.
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