Cattle-clinicalforumstaphaureus

Clinical Forum - Staphylococcus aureusmastitis in cattle Martin Green BVSc DCHP PhD MRCVS
Andrew Bradley MA VetMB DCHP PhD MRCVS
Panel members: Steve Borsberry BVSc DBR CertCHP MRCVS
Jonathan Harwood BVetMed CertCHP MRCVS
Colin Penny BVM&S CertCHP DBR MRCVS
Chris Watson MA VetMB MRCVS
Andrew White BVMS CertBR DBR MRCVS
INTRODUCTION
even if phagocytosed, Staph. aureus may survive and Staphylococcus aureus is one of the most important worldwide causes of mastitis in cattle. It is responsible for major financial losses in dairy farming and for the culling As well as these intrinsic properties, many Staph. aureus of many cows. Once cows become infected they pose strains have the ability to resist antibiotic therapy. The significant problems. When infections have become following traits are considered important: established, they are difficult to remove and infected cows Production of beta-lactamase, an enzyme that are a potential source of infection to other cows. Well- inactivates penicillin and closely related antibiotics.
managed herds can reduce the prevalence of Staph. aureus Probably around 50% of mastitis Staph. aureus strains intramammary infection to a very low level, because it is produce beta-lactamase and there is evidence that these usually susceptible to basic control measures. However, it is strains are more difficult to cure with all antibiotics.
apparent that not all strains of Staph. aureus behave in the Establishment of abscesses and fibrosis within the same way and those with a more ‘environmental’ mammary gland that reduces penetration of antibiotics.
component are most difficult to control. Clinically, Staph. Movement of Staph. aureus to an intracellular site aureus presents the veterinary surgeon with various where there will generally be reduced concentrations difficulties, some of which will be discussed in this article.
The existence of L-forms that are resistant to IMPORTANT FEATURES OF STAPH. AUREUS
The most notable features of Staph. aureus surround its ability to evade and influence the host immune system.
Staph. aureus can be retrieved from various parts of the cow Much research work involving strain typing has shown that and environment although in most herds, infected quarters important strain differences exist in how contagious, and teats harbouring the organism are probably the main persistent and virulent Staph. aureus may be. Different reservoir of infection.The organism has been isolated from strains have varying properties and these largely govern the head, body, legs and nose of cows, from the hands and how Staph. aureus interacts with the host. Although the nose of people, and from the environment such as the pathogenic roles of all cell surface-associated and secretory milking equipment, bedding materials and watercourses.
factors are not fully established, properties of Staph. aureus Maiden heifers are reported as important carriers and reservoirs of infection particularly in the USA, but the production of various enzymes and toxins, some of which significance of this is less certain in the UK. Recent cause damage to mammary tissue and allow tissue invasion research has highlighted very different behaviour exhibited an ability to survive in the keratin of the teat canal of by different biotypes/genotypes of Staph. aureus and this healthy cows, a substance normally inhibitory to may explain difficulties with managing the disease on some a capability to resist phagocytosis, for example, ‘protein A’ in the bacterial cell wall of some Staph. aureus strains CLINICAL SYNDROMES
binds to the Fc portion of antibody molecules making Staph. aureus mastitis presents with varying degrees of the bacteria unrecognisable to neutrophils severity: peracute, acute, subacute, chronic and subclinical.
CATTLE ● PRACTICE
The chronic and subclinical forms predominate and on a OUTLINE OF HERD DIAGNOSIS
herd basis, are the most important. The peracute form is A herd problem with Staph. aureus can show up in different usually seen as gangrenous mastitis (Fig. 1) and often results ways. Spread of the organism within the herd will result in in death. The acute/subacute form resembles other an increase in new infections and a greater number of moderate cases of clinical mastitis but commonly develops chronically infected quarters. In this case the clinical into a chronic form. Chronic and subclinical mastitis are presentation is an increasing incidence of clinical mastitis often associated with fibrosis, abscessation and blocked or more commonly (because new infections often take the ducts within the gland (Figs. 2 and 3).
subclinical form) an increasing proportion of cows (and therefore bulk milk) with raised somatic cell counts (SCC).
An alternative presentation may be an increase in reported treatment failures or recurrence rate of clinical cases.
Diagnosis of Staph. aureus mastitis is based on bacterial isolation and it is best achieved through the use of laboratories accredited for mastitis culture. A herd screen may be performed on bulk milk, but this lacks the quantitative precision to be anything other than a raw guide to the presence of Staph. aureus intramammary infection within a herd. To estimate more closely the significance of Staph. aureus on the farm, culture of milk Fig. 1: Peracute gangrenous Staph. aureus mastitis in two
hind quarters of a five year old lactating cow. from selected cows is important. Cows with persistently raised SCC should be selected (three consecutive monthly counts >300,000 cells/ml is a useful starting point, although sometimes SCC can be lower than this in cows with Staph. aureus intramammary infection). A Californian Mastitis Test aids identification of infected quarter(s) for culture in high SCC cows. Similarly, milk samples from clinical cases are necessary and these can be frozen (this tends to increase isolation rates for Staph. aureus) and then submitted in batches within 3-6 months of collection.
Whilst sampling of high SCC cows can be pre-arranged and therefore carried out at a milking in conjunction with the vet involved, the provision of a milk sample kit with Fig. 2: . Burst abscess in the left hind quarter of a cow with
instructions for sample collection is needed for the chronic Staph. aureus mastitis. herdspersons to successfully collect samples from clinical Of course, this type of herd monitoring, including bacteriological culture, is ideally carried out as an ongoing scheme to provide an early warning of a pending problem rather than solely in the face of a herd problem.
CONTROL OF STAPH. AUREUS MASTITIS
It is certainly possible to maintain a low herd prevalence with <2% cows infected (in one or more quarters) with Staph. aureus. Since in the majority of herds, the most important reservoirs of the organism are infected cows, most control procedures are based on reducing the probability of spread between cows. However, there are other potential sources of Staph. aureus associated with the environment and these may be of special significance in Fig. 3:. Abscessation and fibrosis in the upper region
particular herds in which the condition is difficult to of the left hind quarter of a cow with chronic Staph.
control with the traditional methods (see later). Sources of CATTLE ● PRACTICE
Staph. aureus outside the mammary gland are also the Antibiotic treatment during lactation
reason why it is virtually impossible to eradicate Staph. Early identification of mastitis is essential and early aureus mastitis from a commercial dairy unit.
implementation of treatment is associated with improved cure rates. The ability to identify clinical There are two overall aims to controlling Staph. aureus.The mastitis varies greatly between herdspersons and stems first is to reduce the prevalence of infected quarters within from observation of the cow, udder, foremilk and in the herds to a minimum, and this effectively reduces the line filters and palpation of the udder.
challenge to other cows. The second is to put in place Bacteriological cure rates with antibacterial therapy measures that minimise the risk of new intramammary during lactation are generally poor (certainly worse infections and this means preventing spread from cow to than during the dry period). Research indicates that a cow and secondarily from environment to cow.
cure can be expected in approximately 20-60% of REDUCING THE PREVALENCE OF STAPH. AUREUS
Conventional therapy following datasheet dose The prevalence of infected quarters within a herd can be regimes of typically one to three intramammary tubes reduced in several ways. Each has advantages and covering one to three days is often insufficient for disadvantages and therefore must be used as appropriate.
Staph. aureus mastitis. Bacteriological cure rates of Important economic decisions have to be made when around 20-30% will be associated with such protocols.
deciding between strategies, although the lack of solid Prolonged antibiotic treatments can be used, and are evidence from independent research in some areas means generally reported to give improved bacteriological empirical decisions sometimes have to be made. Reducing cure rates than conventional regimes.These can be split the herd prevalence of infection is essentially carried out into stop-start therapies (often termed ‘pulse’ by treatment, culling, drying off infected quarters and treatments) and continuous therapies. There is limited ensuring new heifers/cows are uninfected. These are evidence to clearly suggest one regime above another, although biologically, it is intuitive that prolonged continuous treatments will be more successful than the Treatment
pulse treatments, which were originally proposed to As described earlier, Staph. aureus has the ability to resist allow datasheet milk withdrawals to be followed.
conventional antibiotic therapy. Indeed, the poor response Longer treatment protocols (possibly 7–14 days in to therapy has resulted in a multitude of treatment length to simulate a short dry cow treatment) are likely protocols and is always the source of some discussion! One to be most successful for Staph. aureus mastitis but more over-riding difficulty is that most licensed treatment research is necessary to allow evidence based decisions regimes for clinical mastitis are probably too short to to be made.As stated earlier, ensuring milk remains free produce good results for Staph. aureus mastitis. It is from residues is a central issue when undertaking ‘off- imperative that if treatment regimes are used outside datasheet recommendations, diligence is shown with milk There is a rationale for using parenteral antibiotic withdrawal periods. The best practice for this is always to test milk from each treated cow for antibiotic residues after treatments for Staph. aureus mastitis, particularly to the standard withdrawal (7 days minimum), prior to improve penetration of inflamed or intracellular sites.
Again, length of activity may be important with 5 days As well as factors associated with the organism, research has A variety of antibacterial products are available but identified various other factors important in determining comparative trials are sparse. It would seem to make the likelihood of treatment success. Where possible, it is sense for the intramammary antibiotic used to have wise to consider these factors before undertaking good gram positive activity without being susceptible treatment. The following are associated with a poorer to beta-lactamase. Parenteral therapy should have chance of a cure following antibiotic therapy: more than similar spectrum with good penetration of the one quarter of a cow affected, increasing parity, a beta- mammary gland and probably intracellular activity.
lactamase producing strain of Staph. aureus, treatment not started early in the course of the disease, increasingly high Antibiotic treatment during the dry period
SCC, clinical signs of abscessation/fibrosis within the Bacteriological cure rates from antibiotic therapy mammary gland, severe teat lesions, other health problems.
during the dry period are usually in the region 40–80% An outline, and pros and cons of different treatment and therefore the dry period is the time of choice for treating Staph. aureus mastitis. Again, the cow factors CATTLE ● PRACTICE
described above influence the probability of curing a that culling alone is not the answer to a high SCC cow. There is little comparative evidence indicating problem; in the absence of institution of appropriate that any particular dry cow product is best for curing measures to control spread the end result is likely to be just Staph. aureus although it is logical to use one of the various products that have suitable activity and remain at a therapeutic level for a prolonged time through the Drying off a quarter
dry period. Selection of particular dry cow products This is a useful compromise measure, an alternative to has been described elsewhere and is beyond the scope culling the cow or treating infected quarters. Chronically infected quarters are identified and milking of the quarter Dry cow therapy is sometimes supplemented with is ceased for the remainder of that lactation. Antibiotic dry additional antibiotic treatment before drying off, often cow therapy is only used when the other quarters are called ‘end of lactation therapy’ (ELT). ELT may be infused at drying off. This technique works particularly given via the intramammary or systemic routes. It is well for high SCC infected quarters but not during a difficult to objectively assess the efficacy of these clinical episode. It is important to mark the quarter clearly treatments and to know if, when and by how much to prevent accidental milking (common now labour is they improve cure rates over the use of dry cow minimised). Research studies report the use of povidine- therapy alone. Until this is properly established it is iodine or chlorhexidine to ‘stop’ the offending quarter difficult to advise farmers on the cost effectiveness of from lactating but these should only be considered when permanent cessation of milking in that quarter is An alternative strategy to supplement intramammary acceptable - if these measures are adopted it is important dry cow therapy is the use of pre-calving therapy to consider the welfare aspects of this procedure and (PCT). This is administering a systemic antibiotic 1-2 consideration should be given to using appropriate weeks before calving, possibly by using an intracellular analgesia. Cessation of milking in a quarter for one part antibiotic. Again solid evidence is sparse but lactation essentially gives that quarter a prolonged dry supplementary treatment during the dry period when period and is often associated with cure rates of over 50%.
natural cure rates are possibly at their best is biologically plausible if not scientifically proven. What Biosecurity
is certain is that it is important to target these strategies Maintaining a low prevalence of infection means at specific cows - it is worth considering bacteriology minimising the risk of introducing infected heifers or cows pre-treatment (at drying off) as the cure rates achieved (whether bought in or home bred) to the milking herd.An by DCT may already be reasonably high, and again, the individual plan should be drawn up for each farm cost effectiveness of such a strategy is not established.
depending on current infection status and acceptability of risk. In particular, we are concerned with Staph. aureus in this article and various considerations include: Culling a chronically infected cow with Staph. aureus A closed herd is best and should therefore be mastitis achieves both a reduction in herd prevalence and encouraged as clearly the best way to reduce the risk of also a reduction in the risk of subsequent spread of infection. However, it comes with a cost, a current net loss If cows have to be purchased, then a series of of around £600 per cow culled. The decision to cull is investigations/tests should be carried out. This starts unfortunately complex and depends on the herd status in with the history of the herd of origin; it should have terms of somatic cell counts and clinical mastitis and the available evidence of a consistently low SCC and ability within the herd to prevent the spread of infection excellent individual cow SCC and clinical mastitis (see below); the cost of a cull needs to be tempered by the records. Animals to be purchased should have a cost and likely success of treatment as well as by the thorough inspection of the udders, teats and milk potential for spread. With the herd position in mind and before purchase. Any signs of disease prevent purchase.
knowledge of the cow factors described above, a cull/treat Although maiden heifers (pre-calved and newly decision has to be made. An old cow with chronic high calved) are generally less likely to be infected with SCC, CMT positive in three quarters and fibrosed Staph. aureus than cows, there is still a risk of an mammary tissue is clearly more eligible for culling than a infection having occurred in a heifer prior to the first young cow with a recently increased medium SCC, one calving.A problem with purchasing heifers is that there quarter positive on CMT. However, decisions are not will be no historical SCC records and the only ways to always clear-cut and quantification of these decisions is a determine an intramammary infection will be from subject of current research. It is important to remember CMT/SCC after calving and bacterial culture.
CATTLE ● PRACTICE
Therefore, there is good reason to carry out culture on advantage of wearing gloves. Indeed, if gloves become all purchased heifers, but it requires that animals can be contaminated and are not regularly cleaned (and milked separately whilst awaiting results, and returned dried), they may even present an added risk in the to the seller if necessary. Furthermore, Staph. aureus spread of disease. Hands (gloved or not) should not may be shed intermittently in milk and does not always come into contact with the teat end during milking.
elicit a very high SCC, therefore negative results Foremilking of cows is required but again has to be cannot be an absolute guarantee of freedom from undertaken with care. Although it helps in the early infection.Three weekly SCC (< 100,000/ml) and two identification of clinical disease it clearly provides a risk negative cultures from newly calved heifers at least in itself as contaminated milk may be sprayed onto the suggest the risk of infection is very low.
equipment and milker. Several research studies have If older cows or heifers later in the first lactation are shown it is actually associated with an increased risk of purchased, then SCC records provide a means for mastitis and therefore stripping milk carefully into a assessing infection status. No SCC level will guarantee freedom from infection, but a lifetime with SCC If infected cows are milked with the rest of the herd, <100,000/ml may be a reasonable starting point.
the use of a separate cluster and dump line is preferable.
Historical SCC should be supplemented with a CMT Cluster disinfection/pasteurisation after milking an (needs to be negative on all quarters), the absence of infected cow is probably a poor second best. If used, clinical signs (milk, teats and udders) and depending on cluster disinfection is probably best achieved by the farm status and risk attitude, bacterial culture of a flushing with very hot water with disinfectant although pooled milk sample from all quarters.
it should be borne in mind this is far from perfect.
Post milking teat disinfection (PMTD) is widely CONTROLLING THE SPREAD OF
regarded as one of the most important elements for STAPH. AUREUS WITHIN THE HERD
controlling contagious mastitis including Staph. aureus. Control of the spread of infection between cows is based PMTD reduces new infections by killing bacteria that mostly on aspects of the milking routine and a correctly are deposited on the teat during the milking process.
functioning milking machine. The aim is to prevent Another important role is to preserve healthy teat infected milk from one quarter reaching the teat of condition and thereby maintain natural teat defences.
another cow either via the milking equipment or the The most common disinfectants used in the UK are milker, and this should be the over-riding thought when iodine and chlorhexidine based with emollients.
assessing parlour routine and plant function. In most Formulation of dips has been described elsewhere but instances, attention to detail in the parlour is effective in teat coverage is also important in determining minimising contagious spread. Environmental sources are less effectiveness. Correct storage and handling of dips is commonly a problem but when present can prove difficult to vital. Generally dipping with a teat cup gives more manage. Important areas of management are listed below.
reliable coverage than spraying although if carefully and thoroughly used both methods can work. Around 10-12 ml of disinfectant per cow/milking is Milking routine
recommended when dipping whereas at least 15 ml is Milking the infected cows (recurrent clinical cases or recommended when spraying. PMTD should be SCC > 200,000 cells/ml) at the end of milking reduces administered as soon as possible, and certainly within the possibility of spread to other cows. This is of particular importance in herds with a high prevalence of infected cows because it is the best way of reducing Milking plant
the level of challenge and hence the new infection rate.
The milking plant can facilitate transmission of Good in principle, this is often a problem in reality, pathogens by acting as a physical vector to transport depending on the grouping/housing/feeding routines bacteria between cows, by allowing the flow of milk on the farm. There is often insufficient labour between teats of an individual cow and by causing teat nowadays to be parting out selected cows twice daily damage that predisposes to subsequent infection.
Therefore, a clean, well maintained machine with No common towels or rags used between teats.
appropriate milk flow characteristics is essential. Daily Use clean, disposable latex gloves and disinfect and weekly cleaning and maintenance can be carried regularly during milking.Whilst it is common sense to out by the herdsperson according to the manufacturer’s protect dirty cracked hands from contact with the teat, recommendations. A full machine test should be various research studies have failed to show a distinct performed six monthly preferably by an independent CATTLE ● PRACTICE
machine expert. In any Staph. aureus investigation a Jonathan Harwood writes:
machine investigation is essential. If in doubt, consult Environmental sources
Although the spread of Staph. aureus can usually be minimised with attention to the milking routine and plant, research suggests that some strains of Staph. aureus tend to presentation) twice daily for five occasions. Secondly, I may have more of an ‘environmental’ behaviour than others.
recommend a prolonged course of a procaine penicillin/ Indeed, in these instances, changes to the milking dihydrostreptomycin intramammary combination tube procedure have little effect and sources outside the parlour (containing 1 g of procaine penicillin and 0.5 g of have to be investigated. Certainly, various studies have dihydrostreptomycin) once daily into each affected quarter reported that new Staph. aureus infections can occur during for 7-10 days. Appropriate milk withdrawal periods would the dry period and in heifers before first calving, clearly at a time when the milking routine can have no impact on new infections. Staph. aureus has been retrieved from I consider that the success rates for these treatments are various parts of the farm including bedding, yards, enhanced through my being involved in the decision to treat.
feedstuffs, non-mains water sources, farm employees, air, I need to examine the cow as well as the SCC records! equipment and the nose/skin of ‘normal’ cows/heifers! Fortunately, in most herds environmental transmission Colin Penny writes:
appears limited but these other sources need to be considered in herds that do not respond to the common Vaccination
Much effort has been directed towards vaccination/ immune modulation for prevention and treatment of lincomycin (off label). If multiple quarters are affected I Staph. aureus mastitis. As yet, no commercial vaccines are suggest a five-day course of tylosin injection. It is hard to currently available in the UK and it is unlikely that assess the level of success as I rarely recommend treatment vaccines themselves will give the whole answer to bovine in lactation but I would expect a success rate of <40%.
Chris Watson writes:
QUESTIONS FOR PANEL:
1. What is your favoured approach to treatment of
confirmed Staph. aureus mastitis, in a cow that is
definitely going to undergo treatment during
lactation? Approximately what sort of success rate
do you expect?
individual cow. As mentioned by the authors the assessment of success is vital if you are going to retain Steve Borsberry writes:
credibility with clients - they always expect too much.
I still think that the best, and simplest, approach is to use a prolonged course of a suitable intramammary preparation.
You are delivering huge quantities of antibiotics compared with any parenteral approach. Also remember that these days the vast majority of parenteral preparations are by the resultant ISCC). However, the problem is designed to have minimal effect on residues in milk for persuading the farmer that the cow requires treating, obvious financial reasons. With a definite diagnosis of Staph. aureus mastitis a drug that is likely to have beta lactamase resistance should be used. There are several A course of parenteral antibiotics, during lactation, is not options available but it is often difficult to get specific information about the ability of a product to resist the beta CATTLE ● PRACTICE
lactamase activity of Staph. organisms. Use the Steve Borsberry writes:
intramammary treatment once daily for 5 to 7 days but Drying off quarters is a useful method in response to herds always advise a minimum 7-day milk withdrawal, though with a cell count problem. However, in general, it should with some products it may be necessary to test the milk for be viewed as a ‘quick fix’ prior to culling. But, as the article residues as well to be certain. The success is often very points out, if by chance the quarter(s) are milked by much influenced by how soon the decision to treat is accident it has a tremendously adverse affect on BMSCC.
taken. Unfortunately the interval is often too long because a conventional treatment protocol has been tried first Jonathan Harwood writes:
before either a specific diagnosis is made or it becomes I have recommended this method of treatment on several apparent that the mastitis is likely to be Staph.
occasions. However, I am unable to draw any personal Andrew White writes:
Colin Penny writes:
I suggest this strategy in cows with single quarters affected only when the farmer is reluctant to cull but needs to Chris Watson writes:
intramammary tube, usually of cefquinome, every 12 hours Drying off individual quarters is often very successful. It using a total of three, together with an intramuscular may be simple to do but in practice you need to be careful: injection of the same compound on the first and third Be sure the client understands what you mean by occasion. Success with this regime varies from 30 to 60% drying the quarter off. It must be emphasised that this being the highest in young cows in the first 100 days of does not imply the use of an intramammary dry cow lactation, the lowest in old cows particularly in those which were affected in previous lactations and those The quarter that is dried off must be closely monitored towards the end of their present lactation.
for several days to make sure that the mastitis does not If the infection is subclinical, with the farmer not able to A system of identifying the quarter should be used, as detect changes in the milk other than with the Californian the cell count could be very high as the quarter Milk Test, then again I divide our cows for treatment into involutes and it may well be infective for other animals those in the first 100 days of lactation and those beyond for a long period of time. Milking it by accident could that stage. The first group I treat with intramuscular be a risk to milk quality and other cows.
injections of tylosin daily for 5 days, those in the second group I suggest removal from the milking herd to be dried Andrew White writes:
off or used to suckle bull calves. If there are other problems I have had very little success trying to dry off only the with these cows, such as poor fertility or lameness I suggest affected quarter. If individual cell counts are available on removal from the farm.The success of treatment for those a monthly basis and I can see three consecutive high treated is about 75% based on a check cell count 14 days figures just prior to drying off, and I know the existence of Staph. aureus infection in that herd I have used tylosin as a pre-calving treatment, the cow having been dried off 2. Do the panel use quarter drying off as a control
in the usual way with dry cow tubes. This regime has strategy in Staph. Aureus herds? If so, what results
given very satisfying results in some herds but do you get?
disappointing results in others. I am not sure why there Subs hotline: 01635 254911
email: [email protected]
CATTLE ● PRACTICE
3. In practice, what do the panel recommend farmers
Chris Watson writes:
do, and what is realistically achievable, to minimise
There is no practical option for safeguarding against the risk of introducing mammary pathogens when
replacement animals being infected.The best that you can new cows are purchased?
advise is to always try and buy heifers and preferably calve them down on the farm to minimise the risks of infection at Steve Borsberry writes:
or around calving. If adult cows are purchased then screening In general, unless the current and/or previous lactation ISCCs them quickly with a California Milk Test is simple and rapid are available I advise that they could be buying-in trouble.
but needs to be done for several days to be sure. It may be Herds where these ISCCs are not available always give rise possible to use ‘separation’ techniques (see Q4 below) to to some concern/suspicion. Relying on BMSCCs can be make sure newly purchased cows do not contaminate the fraught with danger and there are a couple of scenarios: milking clusters until their status is apparent.
1. In herds with low BMSCCs there can be a significantly low percentage of ‘high cell count’ sub-clinical carriers.
Andrew White writes:
2. BMSCCs can be massaged for a few weeks before the Most of our herds here in Lancashire are, fortunately self- date of the sale by discarding ‘high cell count’ cows’ milk.
contained. If cattle are brought in then they tend to be either newly calved heifers or older cows of high genetic Relying on mastitis records also gives rise to merit with a well-documented cell count history. A clinical examination of all animals is recommended and is 1. Mastitis cases are not necessarily recorded.
usually carried out. It is not easy to detect udder changes 2. Herds with a significant sub-clinical Staph. aureus in a newly calved heifer because of the oedema present.
problem do not appear to have a high incidence of The milk is examined clinically but not many farmers will take samples for culture. Separating the purchased animal and awaiting bacteriology results for longer than I do advise that any milking cow purchased should be the usual five-day return-to-seller time being real milked last. In reality, this tends to be a non starter as on most occasions the cows in question arrive overstocked and require milking ASAP. (Deliberate overstocking for 4. What do the panel consider to be the single most
sale and other purposes, is in my opinion a welfare problem important management policy to control Staph.
and should be actively discouraged). The minimum aureus mastitis?
requirements should be CMT shortly after arrival.
Steve Borsberry writes:
I don’t know how to get round the problem of bought-in The most significant problems to overcome in Staph. aureus dry cows having not necessarily received DCT. I must problem herds is to persuade the client that they have a admit that I do not have any great concerns about bought- mastitis problem.They are aware that they have a cell count problem, and such herds do not tend to have a high incidence of clinical cases. Cows with high ISCCs appear, Jonathan Harwood writes:
to the farmer, not to be too adversely affected regarding Purchasing replacement stock always carries risks since yield. Due to the intermittent excretion of Staph. aureus a even the diseases for which the risks can be considered to negative culture can be difficult to comprehend. The be very low will crop up on occasions. In order to avoid spread can be insidious even on farms that have extremely introducing intramammary pathogens female replacement stock should, if possible, be purchased prior to their first calving. If cows have to be purchased, then enquiries must I have tried separate milking groups, identifying carriers, all be made as to SCC history of the individual cows as well with limited success rates. Staph. aureus herds are chronic as that of the herd as a whole. It is preferable to scrutinise herds and long term alterations to milking practices the SCC records collected at regular milk recordings rather (separate groups, spare units etc. for high ISCC cows) are than to rely on a single figure or two in a sale catalogue.
not accepted by overstretched staff, and there is little point when relief staff fail to abide by the rules. Promotion of Colin Penny writes:
good milking routines is obviously useful in all mastitis Being in a low dairy herd density area this is not an issue control programs but may be of limited value in Staph. for us as almost all our herds are closed and therefore rarely aureus herds, where culling is the only answer to chronic CATTLE ● PRACTICE
Jonathan Harwood writes:
Cull the cows with the worst subclinical mastitis first.This must immediately be followed up with an investigation into the milking machine and how it is used in an effort to prevent another six cows developing a cell count similar to Colin Penny writes:
Attention to parlour hygiene and effective teat dipping are crucial along with continued monitoring of individual SCC data and having clear action plans for dealing with Chris Watson writes:
The most important thing to aim for is to reduce the rate of new infections - self cure, dry cow treatment or culling will then take care of the infection already present. As the source of new infections is the infected cow then the contact opportunities for transfer of infection must be removed. Isolation of the infected cows from the milking plant must be the key policy to implement. A ‘separation’ technique to ensure the infected cow does not contaminate the clusters or the milkers’ hands means that the chances of spread will be markedly reduced.There was a study done in the USA comparing a good isolation technique alone against intensive treatment with antibiotics during the lactation. The isolation technique produced better results showing a marked drop in bulk milk SCC compared with the therapy herds. Isolation or separation techniques sound impractical to the stockperson but there are simple options as described in the article: Change gloves after handling an infected cow Shedding the infected cows at milking into an isolation This approach relies on being able to accurately identify Andrew White writes:
I consider the most important management policy to control Staph. Aureus infection is the strict adherence to hygiene matters in the parlour.This does mean attention to the farmer’s hands, to the cows’ teats and also the machinery involved. The importance of recording systems 1. GREEN M. J., HUXLEY J. N. and BRADLEY A. J. (2002) A Rational Approach to Dry Cow Therapy I - Background and Current Perspectives. In Practice 2. BRADLEY A. J., HUXLEY J. N. and GREEN M. J. (2002) A Rational Approach to Dry Cow Therapy II - Making Logical Treatment Decisions. In Practice CATTLE ● PRACTICE

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