Keeping up to date with developments in bonvine mastitis - Veterinary Practice
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InFocus

Keeping up to date with developments in bonvine mastitis

RICHARD GARD
reports on the 2011 British
Mastitis Conference and finds
that, even after 23 years of these
conferences, there is still a very
great deal about the subject to
be discussed

THE 2011 British Mastitis Conference, at the home of Worcester rugby, attracted some 120 delegates including about a third from veterinary practice. A breadth of corporate attendees with pharmaceutical, hygiene and machinery interests mingled with advisers, academics and dairy industry representatives. All would have found the content of interest. On the face of it, after 23 years of such conferences, it could be supposed that there was little new to say but the expectation bar is continually being raised and it is the detail that is now being interrogated rather than the principles. The use of a hand-held fluorescent adenosine triphosphate analyser was presented by Judith Roberts and Matthew Haslam (Leonard and May Farm Vets) and won the best poster competition. This tool is being used to assess hygiene on dairy farms, from swabs, and has particular application with Bactosan problems and to evaluate the efficacy of pre-milking teat disinfection. The visual demonstration has been shown to be an excellent aid to engage with farmers in tackling cleanliness issues. Further details about the 3M Clean Trace Surface ATP Test are available from 3M. Other posters from developed projects included: Bacterial migration through the teat canal related to liner action (Forbes and Gehm, AHVLA); Strategies to reduce milking duration of individual cows (Edwards and Jago, DairyNZ); Monitor the level of chronic high cell count cows to avoid penalties (Hanks, VEERU and Watson, Wood Vet Group); Mastitis bacteriology and qPCR – myths and realities (Bradley, QMMS Ltd and Biggs, Vale Vet Centre); Association between herd size and somatic cell count for Irish and UK dairy herds (Archer et al, University of Nottingham). Details of the posters and content of the presentations are within the proceedings available from The Dairy Group (bmc@thedairygroup.co.uk). The Conference was jointly organised by The Dairy Group and the University of Nottingham. Morten Dam Rasmussen (Aarhus University, Denmark) discussed the relationship between teat preparation, the lag time before milking units are attached and the milking performance. He highlighted that pre-milking teat preparation is not essential to a high milk production but does influence milk quality, udder health and milking performance. With stripping to detect clinical mastitis, the hand of the milker risks the spread of bacteria between quarters and cows so gloves are important and cleanliness, with a need for clean and dry teats on cluster attachment. It is the method of cleaning the teats, rather than the use of chemicals, that will affect the rate of new infections. Pre-milking teat preparation may lower the number of environmental cases of mastitis but increase the number of cases caused by cow-dependent bacteria. The use of the term “cow-dependent bacteria” may be useful in discussions with herdsmen rather than the term “contagious”.

Milk ejection

Studies have shown that milk ejection may occur with peak lactation cows at unit attachment, whereas late lactation cows require stimulation at least 30 seconds prior to attachment. The start of milk ejection is due to the amount of cisternal milk in the udder. Cows with a low udder fill have milk stored mainly in the alveoli and not available to the milking machine. For late lactation and low fill cows, increasing the lag time before unit application decreased the machine on time, regardless of the time spent on pre-milking stimulation. Consistent attachment 60 to 90 seconds after the beginning of teat preparation can improve milk yield. It is important to apply teat preparation in a consistent manner in order to milk cows gently and quickly. Cows respond to a good routine with short machine on times, excellent teat condition and proper milk out. Four research updates were presented. The detection of mastitis pathogens by real time PCR compared to bacteriology, from clinical (n101) and subclinical (n100) milk samples collected from farms in the Netherlands, was discussed by Anja Rothkamp (Gmbh Diagnostics). PCR targets specific bacteria rather than identification of plate growth with bacteriology. Generally about 30% of milk samples record no growth. In the study 13 samples showed no growth with bacteriology but all recorded pathogens with PCR. It is thought that the bacteria were either growth inhibited or dead, due to antibiotic therapy, or affected by the cow’s immune response. Eleven mastitis-causing bacteria or groups are detectable by PCR. Overall PCR detected over 80% of the pathogens detected by bacteriology with fewer Staphylococcci species being identified but a larger number of minor and major pathogens. Is therapy for the cow indicated by a culture negative but a PCR positive result? Antibiotic sensitivity testing is not available from a PCR sample. The clinical relevance of detecting more pathogens by PCR still needs to be evaluated but application of the technology is progressing. Jon Reader (Synergy Farm Health) outlined his understanding and experience with mastitis vaccines. One of the recognised problems is to develop a successful vaccine that does not trigger a cell-mediated response. An increase in white blood cells risks milk of unsaleable quality. A further concern is that if a specific pathogen is targeted by the vaccine, other opportunistic pathogens may colonise the udder so that eliminating one source of infection leads to a different mastitis problem. The key to success will be a thorough understanding of the disease on a particular dairy unit. E. coli vaccines (J5) enhance the ability of white blood cells to destroy bacteria. Vaccinated cows become infected but have a lower rate of development of clinical mastitis and the duration of clinical infection is reduced. Staph. aureus vaccines target virulence factors including proteins in bacterial cell walls, adhesion factors on bacterial cell walls and slime pseudocapsules. The vaccines have limited ability to prevent infections but enhance the spontaneous cure rate and reduce the number of chronically infected cows that go on to become clinically infected. A reduction in coagulase negative Staph. infections has been recorded.

Vaccine trial

A UK trial of a vaccine containing Slime Associated Antigenic Complex plus J5 is currently ongoing (HIPRA). Further research overseas involves a recombinant TRAP (target of RNA111 activating protein). Expectations are for a decrease in cell count and an increase in milk yield. Despite great activity, an effective vaccine for Strep. uberis is unlikely to be available in the UK for some time. Experience in practice (Startvacc, HIPRA UK) injecting all milking cows every three months has shown the need for standard operating procedures and calendar reminders, particularly to make sure that heifers are vaccinated. Heifers are vaccinated either after entering the herd or beforehand depending on the mastitis situation on farm. Bacteriology is seen as vital to monitor and direct vaccine use. Farmer expectation is mainly to combat clinical mastitis and a reduction of 1.5 cases per month in a 200-cow herd is required to justify the cost. This is only achieved where an effective overall mastitis management plan is in place. Application of the DairyCo Mastitis Plan is considered to be an important requirement. The influence of genetics on mastitis was presented by John Cook (Genus Breeding) and with hundreds of genes involved in mastitis resistance, the identification of single genes to be targeted is challenging. Ongoing selection for mastitis resilience can be more successful by measuring traits such as cell count and clinical mastitis. High Immune Response Technology (HIR) is being applied to identify and select individuals with higher breeding values for immune response traits. Individuals are classed as high (H), average (A) or low (L) immune responsiveness.

Complex disease

High antibody and high cell-mediated immune response animals are sought. A calf identified as a high immune responder will generally maintain that classification as a mature cow. Studies have shown that 15% of a herd are H. This is not enough to allow annual replacements but the avoidance of mating with undesirable outcomes is available through computerised mating programmes. Although mastitis is a complex disease involving multiple strategies, recording of health and fitness traits combined with genetic evaluations is a realistic option. Success is slowed by lack of recording of clinical mastitis and steps to improve this will be welcomed. Preliminary results of a large retrospective study looking at mastitis and infertility were discussed by Chris Hudson (University of Nottingham). The data set consisted of 2,338,025 two-day risk periods from 39,590 lactations and 21,068 cows. Analysis of this data indicates that a case of clinical mastitis close to a risk period is associated with a major reduction in probability of a pregnancy occurring. The greatest effect is when clinical mastitis occurs one to seven days before a risk period. This may be due to management decisions not to serve where oestrus is observed after clinical mastitis or to a suppressive effect on ovulation or expression of oestrus. Early lactation mastitis may have little effect on fertility as cows will not be served anyway. Work is ongoing to explore the relative importance of udder health compared to other influences on overall reproductive performance. There has been much debate about the use of antimicrobials and Jennifer O’Connor (MSD Animal Health) gave a review of the past, present and future. The figures for sales of lactating cow intramammaries have fallen to 1,298kg in 2009 but it is individual cow use that causes contamination. MSD set up a workshop in 2011 to discuss the issues of use and misuse with milk failures and some incidents were recognised human error, where others remain unexplained.

Communication needed

Further discussions within the UK National Mastitis Panel have indicated the need for communication and education about the responsible use of medicines. Also a need to understand the science behind antimicrobials and resistance is considered essential. The unpredictable element is the emotions and fears of the public, reflected by the politicians. The whole industry is urged to work together to ensure that antibiotics are used correctly and responsibly. Nick Cobb (JF Cobb & Sons) manages three dairy herds in Dorset with 800, 610 and 400 cows. Clinical mastitis ranges from 18/100 cows to 45 and 47 cases. The aim is to achieve 20 cases of mastitis per 100 cows or less, to maintain current milk quality and to increase milk sales from the current total of 20 million litres. Clean teats (deep sand in the cubicles), test the milking parlour 3-4 times per year, attention to detail and above all doing the simple things well were emphasised. An important part of the management struucture is the vet and Mark Burnell (Synergy Farm Health) explained his approach to mastitis in large herds. His view is that no vet is indispensable, no vet knows it all and no vet suits every farmer. A team approach is adopted with each herd and communication between all involved is highly important. The vet is a health adviser, not a health manager, and the people involved are interested and are often very well informed. If someone is asked to do something they should understand the reasons. Data are collated at the practice
and discussed on farm. Protocols are developed for everything and posters are put up in appropriate locations. Review dates (often six monthly) are stated, which keeps the topic alive. Each farm has a vet and a vet buddy. The buddy is aware of all procedures, aims and ambitions so that there is no drop in activity due to a lack of veterinary involvement. Mark made the point that operating the veterinary role with large herds is not the role for a vet with a large ego.

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