Cattle veterinarians challenged about their approach to mastitis control - Veterinary Practice
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Cattle veterinarians challenged about their approach to mastitis control

Vetinary Practice reports on a masterclass roadshow on what was described as ‘an evolving disease’

VETERINARY surgeons gathered from all corners of the south-west recently to be challenged about their approach to mastitis control in the light of current knowledge.

For those who have qualified in the past 30 years the approach may have seemed entirely new. Older heads were considering that some of the information may have been the subject of distant lectures and discussions, with the deep recesses of the brain now needing to be interrogated.

Whatever the past experiences of the delegates, the talks raised a number of issues that need to be considered if mastitis in the modern dairy herd is to be controlled.

Boehringer Ingelheim brought together Andrew Bradley, Peter Silley and Andy Biggs to offer their insights in a series of regional events. The Exeter meeting was well attended, with time for discussion after each presentation and over the supper that followed.

Commercial view

From the commercial point of view, a display for Ubrolexin was in evidence. The delegates left with a DVD fronted by Laura Randall (cattle veterinary adviser) with James Allcock (Lambert, Leonard & May) highlighting the practice target of 40 quarter cases of mastitis per 100 cows per year and the rise of Streptococcus uberis.

Drawing on the many research projects and his day-to-day gathering of understanding from the operation of Quality Milk Management Services Ltd, Andrew Bradley presented mastitis as an evolving disease.

Together with the changes that are taking place with the management of dairy cows, so the need increases to monitor the herd, the cows and individual quarters.

Through the use of the modern tools available (e.g. TotalVet software, QMMS Ltd and SUM-IT Computer Systems) it is possible “to estimate the relative importance of different stages of the lactation cycle and better understand pathogen behaviour by categorising clinical mastitis by its putative origin and by tracking and tracing movements of individual cows”.

What is of particular interest is the current understanding of the challenges to the mammary gland. Andrew explained that the gland is challenged by bacteria regularly (probably daily) and yet infection is a relatively rare event. The immune system relies on sentinel cells to recruit white blood cells and other defensive mechanisms. It is not just the volume of defensive cells that is important but also the speed of recruitment. This is noted with cows that have a negative energy balance that exhibit a slow white blood cell migration into the milk.

This raises the debate about the level of individual quarter cell count that is required to present an adequate challenge at the time of pathogen penetration. It also leads to consideration of the role of non pathogens as a possible primer for cell count response. Eliminate all bacteria from the udder and the risk of new pathogenic infection is high.

However, the data show that both low and high cell count cows are at risk from clinical disease, presumably because the low count cow has weak defences initially and the high count cow submits because her defences have been overcome.

It has also been shown that there is not necessarily an increase in the number of clinical cases with low cell count cows but an increase in severity. For herds with a herd cell count below 50,000 cells per ml, there is considered to be the risk of “a devastating clinical event”.

Improve immune status

The need is to find ways to improve the immune status of cows in the herd and to lower the challenge (particularly from the environment) for susceptible cows. The minor pathogens such as Corynebacterium spp and coagulase negative Staphyococcus spp may provide competitive exclusion to pathogens, with a moderate elevation of cell count.

The balance for a herd between cure of existing infections and the introduction of new infections will influence a farmer’s expectation of the success of treatment. Modern analysis tools allow for high quality targeted advice.

Peter Silley discussed the value of synergy when developing treatment formulations. A combination of cephalexin and kanomycin demonstrates an advantage over the individual agents acting alone. The spectrum of activity is broadened but also lower concentrations of each element achieve an enhanced bactericidal kill in combination.

Potential issues

On-going work with the Boehringer Mastering Mastitis 2009 Scheme and analysis of samples received from dairy herds in England, Wales and Northern Ireland at the Vale Veterinary Group laboratory, coupled with cell count appraisal using Herd Companion, was described by Andy Biggs.

The role of ESBL (Extended Spectrum Beta Lactamase) producing Enterobacteriaciae, such as E.coli and Klebsiella, indicate potential issues for extended spectrum cephalosporins. In a trial involving 10 herds, half the farmers scored the clinical effectiveness of Ubrolexin to be between 7 and 10 out of 10.

Back in the days of the development of the five-point plan for mastitis control, the programme was shown to be effective in controlling Staph and Strep infections. Beta lactamase producing Staphs were well recognised and the success of clinical treatment in lactation was low, leading to the much more successful application of dry cow therapy.

Dry cow therapy has the dual role of preventing new infections during the dry period and eliminating existing infections. The use of antibiotic at drying off, in low cell count cows, is being replaced by Orbeseal, with no treatment element, and Andy pointed out the need for more thorough treatment of clinical cases.

Selection issues

There are issues with selecting antibiotic or seal on a cow basis. If 200,000 cells per ml is the point below which the cow receives the sealant and over that the antibiotic or antibiotic plus sealant, some low cell count cows may have a high cell count quarter that will not receive antibiotic.

If more effort is to be placed in achieving more successful lactating cow therapy for clinical mastitis, then the question is raised whether earlier treatment is viable before clinical signs.

Should high cell count sub-clinical cows be treated in lactation to reduce the bacterial challenge to the herd? Should cows with a rising cell count be treated? New infections are the easiest to treat effectively and established infections the least likely to be eliminated. The age of the cow is not linked to the success of treatment.

Changed economics

Original protocols were for an extended treatment period in lactation but this lost favour with the need for the farmer to reduce milk wastage following treatment.

The economics have changed and many farmers are more concerned about a rise in cell count and so a more thorough approach to treatment in lactation is being investigated.

Clinical flare-ups are a concern and the overall mastitis history of the herd, the prevention of the spread of infection including teat dipping performance, the infections detected and the role of minor pathogens are factors for consideration.

Strep. uberis infections include cow adaptive strains, which respond poorly to treatment and have the ability to rapidly break down casein to release amino acids to feed on. Andy highlighted the need to identify circumstances where the outcome is likely to be poor and added: “Don’t treat infections that are untreatable.”

The speakers certainly stimulated a thinking approach to mastitis control utilising the latest analysis tools.

It is likely that the answers to many of the questions may be found in the reference textbook, Mastitis in Cattle, by Andy Biggs. What is certainly clear is that as mastitis is evolving, there is a need for regular information updates and new levels of understanding.

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