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Mastitis
Mastitis is an inflammation
of the udder and is common in dairy herds causing important economic losses. It
cannot be eradicated but can be reduced to low levels by good management of
dairy cows.
Of the several causes of
mastitis only microbial infection is important. Although bacteria, fungi, yeasts
and possibly virus can cause udder infection the main agents are bacteria. The
most common pathogens are Staphylococcus aureus, Streptococcus agalactiae,
Str.
dysgalactiae, Str. uberis and Escherichia coli though other pathogens can cause
occasional herd outbreaks. Mastitis occurs when the teats of cows are exposed to
pathogens which penetrate the teat duct and establish an infection in one or
more quarters within the udder. The course of an infection varies, most commonly
it persists for weeks or months in a mild form which is not detected by the
stockman (ie. subclinical mastitis). With some pathogens, typically E. coli, the
infection is frequently more acute and there is a general endotoxaemia with
raised body temperature, loss of appetite and the cow may die unless supportive
therapy is given. When clinical mastitis occurs the effective therapy is a
course of antibiotic infusions through the teat duct. These nearly always remedy
the clinical disease and often eliminate the bacterial infection. Infections may
spontaneously recover but most persist to be eliminated eventually by antibiotic
therapy or when the cow is culled. The susceptibility of cows varies
considerably and new infections are most common in older cows in early
lactation, at the start of the dry period and when the management is poor.
Mastitis causes direct
economic losses to farmers in several ways. Milk yields are reduced, milk that
is abnormal or contaminated with antibiotics is unsaleable, there are veterinary
and antibiotic costs, a higher culling rate and occasional fatalities. The milk
processing industry also incurs losses because of problems that result from
antibiotic in milk, and the reduced chemical and bacterial quality of mastitic
milk.
Infectous Mastitis
Mastitis microorganisms,
usually bacteria, originate in various sites on the cow. They multiply in
various ways and are spread from cow to cow.
Most common types of mastitis
bacteria originate in the udders of infected cows and in sores on tests. These
pathogens multiply in teat sores and are spread during milking.
The several microbial
diseases of the udder that are collectively known as mastitis are distinctly
different. The pathogens can arise from different primary sites, they multiply
in different environments and therefore the timing of the exposure of the cow to
the bacteria will vary. Subsequently the acuteness and persistency of the
infections differ and also the probability of cure when therapy is given.
The commonest forms of
mastitis in most countries are caused by S. aureus and Str. agalactiae. The
primary sites of these is the milk of infected quarters and therefore they are
spread mainly at milking, either during udder preparation or on hands and
milking machines. These pathogens can colonise and multiply in teat sores and in
teat ducts and this greatly increases the degree of exposure of the teats to
bacteria. They usually cause chronic infections which persist in the subclinical
form and occasionally become clinical when abnormal milk can be detected.
Systemic infection with loss of appetite and raised body temperature is
infrequent. When suitable antibiotic preparations are infused into the udder the
clinical mastitis nearly always subsides and most Str. agalactiae infections are
cured but with staphylococcal infections the cure rate is poor and most persist.
Infections caused by Str.
uberis and E. coli are often called ‘environmental’. The main primary sites of
the pathogens are bovine, but not from within the udder. These do not normally
colonise teat skin and the multiplication occurs in organic bedding materials
(eg. straws and sawdust). These types of infection are most common in housed
cattle in early lactation and whilst they can cause persisting subclinical
mastitis the more typical from is clinical mastitis soon after the onset of the
infection, and with coliform mastitis the endotoxaemia causes raised body
temperature and marked reductions in milk production. Str. uberis infections
usually respond to therapy but with E. coli infections it is important to give
supportive treatment to overcome the endotoxaemia and if this is successful
spontaneous recovery usually follows.
Str. dysgalactiae is similar
to Str. agalactiae and S. aureus in that it can readily colonise and multiply in
teat lesions but the main primary site is not the milk of infected quarters, but
other bovine sites. The course of the infection is not dissimilar to Str.
agalactiae and infections respond readily to antibiotic therapy.
Many other microorganisms can
cause mastitis. These less common forms are not usually important but
Pseudomonas and Mycoplasma bovis does cause serious problems in a few herds.
Although the pathology of the
various types of infection show distinct differences the causes of infection can
be diagnosed with certainty only by bacteriological tests made on aseptically
taken quarter milk samples.
CAUSES OF MASTITIS
An udder quarter becomes
infected when:
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the teats are
exposed to pathogens
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the pathogens
penetrate the teat duct
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the infection is
established within the udder
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Exposure to Pathogens
All dairy cows are
continously exposed to pathogens that can cause mastitis but new infection is
normally infrequent. This is because the exposure to pathogens is usually small.
The number of pathogens in the milk of infected quarters will vary from less
than 1000 to many millions per ml of milk but it is usually less than 10,000 per
ml and further diluted by the milk from the majority of uninfected quarters. The
number of pathogens on clean pasture will be extremely small. The exposure of
cows teats to S. aureus, Str. agalactiae and Str. dysgalactiae will be greatly
increased when teat sores and lesions on teat ducts are colonised by these
mastitis pathogens or when cows lie on contaminated bedding or corrals.
Occasionally the exposure will be increased from improperly cleaned milking
equipment or through udder washing with contaminated water. This can be avoided
by adopting simple methods of cleaning equipment .
The most effective way of
reducing the exposure to S. aureus, Str. agalactiae and
Str. dysgalactiae is by
dipping or spraying the teats in disinfectant immediately after milking. A
number of disinfectant products are available and good results are obtained with
hypochlorite, iodophor and chlorhexidine. Teat disinfection greatly reduces
residual contamination and more importantly encourages healing of teat sores and
lesions and also prevents the growth of pathogens in teat ducts (ie.
colonisation). Other practices such as udder washing with disinfectant, rinsing
milking equipment after each cow is milked (eg. back flushing) will also reduce
exposure but their effects are smaller than teat dipping because they do not
influence the colonisation of teat sores and ducts. To maintain low levels of
exposure it is most important to maintain healthy teat skin and avoid sores,
chaps and any form of teat damage. To maintain good teat condition emolients or
salves (eg. glycerol) can be added to most teat dips but not to hypochlorite.
While soil and fresh bedding
materials are usually relatively free from mastitis pathogens they can develop a
very large pathogen population (>106/gm) within a few days given the optimum
conditions of moisture and temperature. Inevitably bedding becomes moist and
contaminated with faeces and given sufficient warmth the growth of E. coli and
Str. uberis is rapid causing outbreaks of mastitis. This can be prevented by
avoiding using muddy corrals and by keeping cows on clean pasture. When cattle
are housed on straw or sawdust in yards or in cubicles (freestalls), it should
be replenished frequently, preferably daily. Straw yards should be cleaned
completely if outbreaks of clinical mastitis occur. For cows kept in cubicles
sand can be used successfully as a non-organic bedding material in which
coliforms and Str. uberis do not readily multiply.
Penetration of the Teat Duct
The healthy teat duct (streak
canal) is extremely effective in preventing the passage of pathogens into the
udder and it is the cows most natural barrier against mastitis infections. It
not only acts as a physical barrier against penetration but the lining of the
duct also contains secretions that inhibit bacterial growth. Pathogen
penetration can occur during milking, in the intervals between milking and even
when cows are not lactating. If pathogens penetrate during milking they may be
flushed out otherwise infection usually occurs. It is most important to
recognise that even when very small numbers of pathogens (eg. less than 20)
penetrate the duct infection usually occurs. Apart from the increased rate of
penetration that occurs with high rates of exposure there are other factors in
cattle management that are important. These occur with faulty machine milking
and also if milkers insert contaminated objects (eg. dirty treatment syringes)
through the teat duct.
Under certain milking machine
conditions there are considerable vacuum fluctuations in the teat cup liner
below the teat. In the resulting turbulence the milk which is normally flowing
away from the teats returns to the teat through the short milk tubes (ie.
reverse flow or impacts). These impacts can have sufficient force that the
pathogens carried in the milk penetrate into or through the teat duct causing
infection. These infections can be reduced by using a milking machine fitted
with liners that do not slip during milking, that have adequate diameter short
milk tubes and an effective airbleed in the clawpiece. Even better protection is
achieved by using liners fitted with ‘shields’ or milking with ‘non-return
valves’ in the milking machine cluster.
Inserting instruments through
the teat duct should be avoided but when necessary (eg. for therapy) the teat
end should be scrubbed with disinfectant for 15 seconds before insertion and the
instrument must be sterile. If in doubt about sterility the instrument should be
placed in boiling water for at least 30 seconds, but if this is impractical it
should be scrubbed in surgical spirit (70% ethanol).
Establishment of Infection
A number of antimicrobial
systems occur in the bovine udder and milk but they appear to be relatively
ineffective in preventing infections though they are important in reducing the
severity of infections and to a lesser degree in eliminating infections. The
hosts defences are partly cellular (leucocytes) and immune defences and in
addition there are non-specific defences provided by complex biochemical systems
including enzymes and other constituents of milk. Although most types of
infection tend to persist for months if untreated the cellular defences will
eliminate most E. coli infections providing the cows cellular response to
infection is rapid.
This brief description of the
prime importance of pathogen exposure, duct penetration and the establishment of
infection deals only with the main aspects that are important in considering
mastitis control. The interactions are more complex and not fully understood.
There are other physiological and environmental factors which are or appear to
be important in particular herds. These include nutrition, heat stress and
factors such as age of cow and stage of lactation.
Elimination of Infection
Apart from E. coli infections
most persist if untreated until eventually there is spontaneous recovery or the
cow is culled. This persistance of infection for weeks, months and years with
staphylococcal infections is an important characteristic of mastitis which must
be taken into account in devising a disease control.
Because spontaneous recovery
occurs infrequently and there is no proven way of increasing it the introduction
of antibiotic therapy was a major advance in controlling bovine mastitis.
Infusing antibiotics via the teat duct into the udder is a simple way of
overcoming nearly all clinical mastitis and of eliminating many infections. Many
antimicrobial drugs are used in formulating products for mastitis therapy (eg.
penicillin including the semisynthetics, streptomycin, aureomycin). The
effectiveness of the drug will depend partly on the sensitivity of the pathogen
treated to the drug used and also to the way the drug is formulated. This
influences the absorption, distribution, metabolism and excretion of the drugs
from the milk. No antimicrobial drug is ideal for all conditions and mixtures
are used to be effective against a range of pathogens (ie. ‘broad spectrum’) for
use in lactating and dry cows. Nearly all therapy is given without prior
knowledge of the causative pathogen. Under these conditions treating quarters
exhibiting clinical mastitis with basic standard products gives a
bacteriological elimination of 75–90% of streptococcal and about 30% of
staphylococcal infections. The cure rates of Mycoplasma and
Pseudomonas
infections are lower. If the treatments are given after the final milking of
lactation (ie. dry cow therapy) using formulations designed for this purpose the
cure rates are improved and are about 50% for staphylococcal infections. The
rates of elimination of staphylococcal infections varies considerably between
herds and are lower in cows with more than one infected quarter and those with
more severe clinical mastitis.
Antibiotic therapy is usually
given as infusions of solutions through the teat duct but this should be done
only after careful cleaning of the teat orifice with a disinfectant swab. To
avoid infusing contaminated antibiotic, use only factory made disposable
syringes. A course of therapy is often 2 or 3 infusions at 24 hour intervals,
rejecting the milk from the cow for 2 or more days after the last infusion to
avoid antibiotic contamination of the bulk milk. Although nearly all cases of
clinical mastitis respond quickly it may take several days before the milk
becomes normal. Treatment, the choice of antibiotic and the milk reject time
should be on veterinary advice and when there are severe persistent infections
systemic administration of antibiotic may also be used to overcome the
endotoxaemia.
Many infections are
eliminated by culling cows and this can be increased by the sale of cows with
persistant clinical mastitis.
Principles of Mastitis Control
Mastitis cannot be eradicated
but can be reduced to low levels by adopting simple economic management routines
that relate to the patterns of infection. Currently it is not possible to base a
control on vaccination and although cows susceptibilities are largely inherent
there are major practical limitations to control through breeding, and progress
would be slow. Therapy is invaluable to contain the problem but cannot be the
basis of a control which must depend on preventing new infections. In
practice the key to control is good cattle management particularly steps to
reduce exposure to pathogens and also the planned use of antibiotic therapy.
Because control depends on management the steps must be simple and economic and
fit easily into a milking routine.
There are three main patterns
of infectious mastitis.
The first type is the most common
and is caused by Streptococcus agalactiae, Staph. aureus and
Str. dysgalactiae.
These infections usually persist as subclinical infections and this persistance
is important. Even if the rate of new infection is considerably reduced the
proportion of infected quarters will decline slowly over several years, unless
the duration of infection is also reduced. In addition to general good
management including sound milking methods, teat disinfection (ie. dipping or
spraying) is particularly useful to prevent these infections, by reducing
exposure to pathogens. To reduce the persistance of infection the key step is
dry cow therapy.
The second type of infection
occurs mainly in housed or closely corralled cattle and is typified by acute
clinical mastitis in early lactation. The main pathogens are Str. uberis and E.
coli and their epidemiology is such that they are not controlled by teat
disinfection . Drying off therapy is useful in preventing Str. uberis
infections that commonly occur early in the dry period but it will not reduce
the Str. uberis and E. coliform infections occurring at, and soon after,
calving. Control depends primarily on reducing the exposure to pathogens by
moving cattle regularly to clean corrals or providing clean bedding, preferably
daily.
The third type of infection
occurs in non-lactating cows. These are common in the early part of the dry
period particularly with Str. uberis and most persist causing clinical mastitis
in the following lactation. Another form common in N. Europe occurs later in the
dry period and is caused by a complex infection with Corynebacterium pyogenes,
Peptococcus indolicus and Streptococcus. This is ‘summer’ or ‘heifer’ mastitis
and its aetiology appears to require exposure to pathogens carried by a species
of fly. Control is achieved by drying off therapy and fly control.
It is important to recognise
that because most mastitis is subclinical and unseen control depends primarily
on adopting sound management routines for the whole herd. It cannot be achieved
by using laboratory tests to identify individual infected cows and taking
special action with these animals. Tests are useful to alert farmers to the
extent of the problem but they rarely indicate steps additional to those that
should be in the daily routine.
In a concise monograph it is
impossible to cover the causes of all types of mastitis. Infrequently a herd
mastitis outbreak will occur with an unusual pathogen even when the farmer
adopts good control routines. The solution of this type of problem does require
investigation by a veterinary diagnostic laboratory in order to discover the
source of pathogen and the aetiology.
Control Methods
The following routine will
reduce the proportion of infected cows and clinical mastitis by at least 70% if
used regularly at each milking. Mastitis caused by Str. agalactiae will be
reduced to very low levels and is frequently eradicated.
1. Adopt good cow
management practices as the essential basis for a mastitis control routine (eg.
feeding, housing, hygiene). Mastitis is unlikely to be controlled with
neglected, underfed cows kept under stress in dirty conditions.
2. Reduce exposure to
pathogens
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Clean thoroughly
all equipment used when milking
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DO NOT HOUSE OR
CORRAL CATTLE UNDER DIRTY CONDITIONS, preferably CHANGE ORGANIC BEDDING
MATERIALS DAILY or use sand for bedding
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Wash dirty udders
before milking with clean running water preferably with the hand, a disposable
paper towel or a disinfected cloth and dry thoroughly. Do not wash with
contaminated cloths and water
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DIP OR SPRAY ALL
TEATS AFTER MILKING WITH DISINFECTANT TEAT DIP (eg. hypochlorite, iodophor,
chlorhexidine)
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Adopt practices
that prevent the occurrence of teat lesions (sores, chaps and teat damage). If
they occur use a teat dip or spray containing a emolient.
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If practical milk
clinically affected cows last
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Additional
benefits can be obtained by disinfecting hands before milking each cow, using
individual paper udder cloths, dipping teat cups in disinfectant before each cow
is milked, and ‘back flushing’. These reduce bacterial exposure but their
effects are secondary to those described above
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3. Reduce the chances
of pathogens penetrating the teat duct by:
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avoiding teat
injury or fly attack
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using a milking
machine that is correctly tested, and maintained
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using a milking
machine modified to prevent ‘reverse flow’ and ‘impacts’
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minimise the
effects of vacuum fluctuations by avoiding ‘linerslip’, fitting ‘shields’ or
‘non-return valves’ into short milk tubes or liners.
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4. Reduce the
duration of infections by
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detecting clinical
mastitis by examining foremilk or fitting ‘mastitis detectors’ into the long
milk tubes
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giving
intramammary infusions of antibiotics under veterinary supervision to clinically
affected cows and KEEP A RECORD
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TREATING COWS AT
DRYING OFF with infusions of antibiotics recommended by a veterinarian
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CULL COWS WITH
REPEATED CLINICAL MASTITIS.
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5. Reduce mastitis in
nonlactating growing cattle or cows in the dry period
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Avoid using low
lying grazing land and damp wooded areas where flies are common. Move cattle
from pastures known to give problems with mastitis
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Adopt good fly
control measures
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TREAT COWS AT
DRYING OFF with antibiotics recommended by veterinarian. All cows should be
treated, alternatively treat cows that have previously shown signs of infection
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NOTE THE REDUCTION IN
INFECTION IS NOT IMMEDIATE BUT LEVELS FALL BY ABOUT 50% IN ONE YEAR AND CONTINUE
TO FALL IN SUCCESSIVE YEARS
Organisation of Mastitis Control
World experience indicates
that if farmers are to control mastitis successfully they require some technical
and laboratory assistance. This can be provided by government agencies,
cooperatives or the milk collecting dairies. The support should:
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provide an
extension service (veterinary, animal husbandry and milking machine technology)
to ensure that farmers receive the correct information on the best routines to
follow for their environment
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report regularly
to farmers (eg. monthly) giving the results of appropriate tests made on herd
bulk milk to indicate the progess made in reducing mastitis
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ensure that good
milking equipment, disinfectants and antibiotics are available
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investigate the
causes of failure in herds adopting the recommendations but
not making progress
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Although laboratory support
is essential it is important to recognise that mastitis is widespread and for
successful control in a national herd or the herds in a cooperative it is
necessary that most, preferably all, the herds carry out the routine. A
control that concentrates on improving the worst 10 to 20% of herds will have
little effect on the total problem of mastitis. EFFECTIVE MASTITIS
CONTROL DEPENDS ON FARMERS REGULARLY FOLLOWING THE SIMPLE MANAGEMENT PRACTICES.
Tests will not often provide information that leads to special action for
farmers to take that is additional to what they should be doing.
Tests for Mastitis
The tests for mastitis are
either microbiological, to detect the causative pathogen , or
tests for the changes in the composition of milk which occurs with the
inflammation. Tests for pathogens are not required routinely but are necessary
to investigate special herd problems. The tests for changes in milk composition
are simpler and some may be carried out on the farm (eg. California Mastitis
Test). Electronic automated laboratory tests for somatic cells in milk (eg.
using Fossomatic or Coulter equipment) can be used to provide regular
information to farmers. Many other tests are also available which measure
specific biochemical changes in the composition of milk (eg. Bovine serum
albumin (BSA); antitrypsin test and NAGase test). The most widely used for
routine screening of farm bulk milks is electronic cell counting which can
readily be integrated with other tests of milk composition. When it is necessary
to detect abnormal quarters on the farm a simple cowside test is useful (eg.
CMT).
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