Mastitis is considered one of the most costly diseases of dairy cattle and one of the most common reasons for antibiotic treatment
on dairy farms. There are numerous treatments (both antibiotic and non-antibiotic) for clinical mastitis. The majority of
cows with clinical mastitis are treated with antibiotics but a study regarding on-farm culture indicated that withholding
treatment pending culture helps reduce antibiotic usage (Neeser et al., 2006). Prior to the year 1994, there were very few
studies of mastitis treatment efficacy that utilized non-treated control cases. Although it is well-known that the efficacy
of a given treatment depends largely upon the agent of mastitis (Ødegaard and Sviland, 2001), few studies evaluated the effect
of treatment on specific mastitis agents. Pirlimycin is highly effective against Streptococcus agalactiae but has no effect against Escherichia coli. Approximately 80% of clinical mastitis due to E. coli are mild to moderate cases and > 90% of these cases undergo spontaneous cure within a few days. Thus, an efficacy study
of pirlimycin for "clinical mastitis" might suggest that pirlimycin is an effective antibiotic for E. coli. The severity level is also associated with the efficacy of a given product (Ødegaard and Sviland, 2001). There are various
other factors that might alter the interpretation of the results of a clinical trial. A 2004 study identified severity of
mastitis, lactation number, previous mastitis this lactation and bacteriological findings as factors that influence outcome
of treatment and these factors appear relevant as stratification factors in mastitis trials (Hektoen et al., 2004a). To answer
the question in the title, progress is being made as more studies utilize non-treated control cows and employ various measures
to appropriately gather and analyze treatment data.
Qualities of a Sound Treatment Efficacy Study of Clinical Mastitis
1. Should be naturally occurring cases of clinical mastitis.
2. Must have a non-treated control group or a good reason for their absence.
3. Must define treatment outcome parameters and have the parameters as objective as possible.
4. Investigator must have full control of the cows
5. Culturing should occur prior to treatment, once during treatment, once immediately after milk withdrawal time,
and once 3-4 weeks after the first treatment. For studies with chronic pathogens (e.g. Staphylococcus aureus), cultures should be continued for several months.
6. Treatments must be assigned randomly and the method of randomization should be declared.
7. Treatment outcomes should be assessed by severity level (mild, moderate, and severe).
8. Treatment outcomes should be assessed by etiologic agent.