Extended antibiotic treatment of persistent bovine mastitis during lactation: Efficacy, economics and social influences

Mastitis is an inflammation of the udder caused by bacteria that invade the udder through the teat canal, causing either persistent intramammary infections, or short, transient infections. Mastitis is the most costly disease on a dairy farm because it directly affects the production of milk, the primary source of income for the dairy farmer. Mastitis can be visible (clinical mastitis) or invisible (subclinical mastitis). A large proportion of farmers repeats antibiotic treatment after initial standard treatment according the label claim, thereby extending the duration of treatment. The aim of the thesis is to evaluate the bacteriological, clinical and economic efficacy of extended antibiotic treatment of persistent mastitis during lactation compared to standard treatment. An additional aim was to explore the social influences on farmers with respect to the duration of antibiotic treatment of clinical mastitis. The economic outcome of lactational treatment of persistent subclinical Streptococcus uberis, Streptococcus dysgalactiae and Staphylococcus aureus mastitis is highly dependent on the farm, cow and pathogen involved. Extended 8-day lactational treatment is profitable only for very valuable animals, on farms where the risk of pathogen transmission is high and/or on farms where the farmer is likely to cull a high percentage of cows with subclinical mastitis. Although clinical efficacy of extended 5-day treatment of clinical Staph. aureus mastitis was better than a standard 1.5-day cefquinome treatment, bacteriological efficacy was not different. Clinical efficacy of extended 5-day cefquinome treatment, compared to a standard 1.5-day intramammary cefquinome treatment of recurrent clinical mastitis cases from an environmental origin (E. coli and Strep. uberis), showed an improved clinical outcome compared to standard treatment. Overall bacteriological cure of an extended, 5-day intramammary cefquinome treatment of clinical mastitis cases of cows with a persistent cow SCC above 200,000 cells/mL, was not different from a standard, 1.5-day treatment. Extended antibiotic treatment seems to be only indicated when mastitis cases are caused by streptococci, specifically Strep. uberis. These results indicate that extending treatment of clinical mastitis with cefquinome should not be routinely recommended. Qualitative interviews to determine social influences on farmers related to the duration of treatment of clinical mastitis, showed that farmers’ want to treat mastitis ‘thoroughly’, until clinical symptoms have disappeared. They believe that a ‘good farmer’ treats mastitis ‘thoroughly’, otherwise it may persist or recur. Extended treatment seems to be part of the social norm of ‘being a good farmer’. Social approval reduces insecurity of potentially being perceived as a poor farmer and thus, extended treatment is emotionally rewarded. Prudent antibiotic use of antibiotics is potentially hindered by perceived subjective norms on duration of treatment. The thesis showed that extending antibiotic treatment of persistent bovine mastitis during lactation is widely applied but is not always better than standard treatment with respect to bacteriological, clinical and economic efficacy. A higher efficacy of extended antibiotic treatment of persistent mastitis may be limited to specific farms, cows, pathogens and antibiotics. The farmers’ decision to extend treatment was shown to be not only based on rational arguments but also on subjective beliefs