membranes. Fluoroquinolones have a broad-spectrum of activity extending to
Gram-negative pathogens. Hence, injectable fluoroquinolones are now licenced
for the treatment of acuteE. colimastitis in Europe. Some late-generation cepha-
losporins, such as cefquinome, can also be used systemically for the treatment of
acuteE. colimastitis.
During the dry period, the presence of infection has a fundamental and lasting
influence on the health and productivity of the dairy cow (Green et al. 2002 ). The
effects are reduction in subsequent milk yield in infected quarters, reduction in milk
quality (increased SCCs, decreased butterfat and protein content) at the next
lactation and a greater risk of subsequent clinical mastitis. Historically, when the
five-point plan was instituted, the principal value of DCT was to eliminate infec-
tions caused byS. aureusand various streptococcal species that persisted during
lactation. Indeed, a more effective bacteriological cure is achieved by treating cows
at dry off than during lactation (Smith et al. 1967 ). In the modern dairy herd,
however, the primary objective of DCT is prevention of new intramammary infec-
tions, the prophylactic goal being a reduction in the risk of clinical mastitis during
the subsequent lactation. To achieve this, the systematic use of broad-spectrum
antibacterial agents at drying off is not always necessary, and a more discriminating
approach can be applied (Bradley et al. 2003 ; Pyo ̈ra ̈la ̈ 2008 ). Such an approach
involves selection of the cows that are likely to be uninfected. In practice, this can
be done by verifying their recent SCC records (they should be consistently lower
than 200,000 cells/mL) and any mastitis history in the previous lactation (there
should be no mastitis experienced in any quarter). Once identified, these cows are
dried off with either (a) an antibiotic with known efficacy against the predominant
environmental pathogen(s) identified within the herd or (b) an internal teat sealant
infused alone, that is with no antibiotic. Using this approach, cows with SCCs
greater than 200,000 cells/mL for at least two recent records, including the last one
prior to drying off, are assumed to be infected, and they are investigated to identify
the pathogen(s) involved; these cows receive a suitable antimicrobial drug as DCT,
either alone or preferably followed by infusion of an internal teat sealant to prevent
new infections.
A recently conducted UK-based field efficacy study highlighted the benefits of
combination DCT in cows with high SCCs. This study in high SCC cows compared
DCT with 600 mg cloxacillin alone and 600 mg cloxacillin followed by an internal
teat sealant (Newton et al. 2008 ). Ten dairy herds were involved, and 283 cows
were included in the data analysis. Clinical mastitis cases were monitored from
drying off until 100 days after calving. In the quarters, given the combined
treatment, there were 23 cases of clinical mastitis compared with 50 cases in the
quarters that received the antibiotic alone; differences in both the mastitis episodes
and quarters affected were significant (P<0.01). A summary of the pathogens
isolated from these cases of mastitis is given in Table 5. In the quarters treated with
antibiotic alone, there were significantly more cases of clinical mastitis caused by
S. uberis(P¼0.02) and coagulase-positive staphylococci (P¼0.03).
The likelihood of a quarter either being bacteriologically negative after calving
or developing clinical mastitis in the first 100 days after calving was investigated
126 H. Benchaoui