Streptococcus agalactiae subclinical mastitis epidemiology and control in Colombian dairy herds

Bovine subclinical mastitis produced by Streptococcus agalactiae (S.agalactiae) is a priority in the emerging dairy industries of countries like Colombia. The objective of this thesis was to provide a comprehensive exploration of the S. agalactiae problem in Colombian specialized dairy herds, in order to control this prevalent pathogen. The first research chapter using a longitudinal database from bulk tank milk somatic cell counts (BTSCC) of the Northern region of Antioquia, showed that milking by hand, fore stripping, and failing to post-dip were associated with the BTSCC variation. The second chapter, investigated the herd level risk factors for S.agalactiae Bulk tank milk (BTM) status of herds from the coffee region of Colombia, indicating that the S. agalactiae BTM prevalence was 23.4% and 59.6% of the herds were positive at least once during the study period. Biosecurity variables, milking practices, proportion of cows culled, and manual milking were associated with the BTM status. The third research chapter, using quarter-based measurements over two years, determined that 9.7% of the records experienced S. agalactiae new intramammary infections per lactation (NIMIs), and that S. agalactiae herd prevalence, milking by hand, previous intramammary infection with Staphylococcus aureus, age of the cow and days in milk, were associated with the incidence rate of S.agalactiae NIMIs. The fourth chapter, using two molecular typing methods, found low molecular variability of S. agalactiae, and suggested a limited number of sources of infection for these herds, with potential inter-host transmission of the pathogen. The final chapter, through a clinical trial, found that the cure risk after an initial treatment with an intramammary product was higher (82.4%) than the intramuscular therapy (65.8%), with no difference in the cure risk of refractory cases after re-treatment. These research findings will provide the tools to stablish effective S. agalactiae control programs in the country in order to improve the milk quality and the well-being of dairy producers in Colombia