E coli mastitis
Dry Period: Risk Factors and Prevention
Martin J Green BVSc DCHP MRCVS
Orchard Vet Gp, Wirrall Park, Glastonbury, BA6 9XE, UK / University of Warwick, Coventry, CV4 7AL, UK
Andrew J Bradley MA VetMB DCHP PhD MRCVS
University of Bristol, Langford House, Langford, Bristol BS40 5DT, UK
ABSTRACT

The importance of new infections during the dry period, prolonged sub-clinical infections and
recurrent mastitis with gram-negative organisms, has been examined in UK conditions.

Control methods for gram-negative mastitis need to include measures for the dry and periparturient period.

A dry cow therapy trial, showing product efficacy against gram-negative clinical mastitis, will
be described, as well as other control measures applicable to the dry period.
Key Words - Mastitis, coliform, E coli, prevention, dry period, dry cow therapy.
INTRODUCTION
Gram-negative organisms (eg. E coli, Klebsiella spp, Enterobacter spp, Serratia spp and Citrobacter spp)
remain a significant cause of bovine mastitis. On dairy units with bulk somatic cell counts below
250,000/ml, they often account for between 30 - 50% of clinical mastitis, and the incidence of clinical E
coli episodes does not appear to be reducing (Booth 1993, Barkema 1998, Bradley and Green 2000,
Peeler 2000, Huxley 2000). Prevention of mastitis caused by the gram-negative pathogens has largely
been based on two management strategies; minimising teat contamination and reducing the chance of
organism penetration during or after milking or around calving. New information on the behaviour of
these organisms has been described in the previous paper and the aim of this paper is to discuss how the
cattle practitioner may incorporate these ideas into a preventive strategy for coliform mastitis.
Current measures
It is not the intention of this paper to review in detail measures that are currently recommended for the
control of gram-negative mastitis. For more information, reference can be made to Blowey and
Edmondson, (1995), Green (1998) and Smith and others (1993). Areas of control have been described as
below:
 Minimise teat contamination through good housing design and environmental hygiene (of the calving
and lactating accommodation and loafing yards after milking).
 Reduce the chance of organism penetration at milking time by ensuring teats are clean, disinfected
and dry prior to milking, and that correctly functioning milking equipment is used.
 Reduce the chance of infection before or after milking by ensuring hygiene of yards and provision of
fresh feed after milking to discourage cows from lying down.
 Other factors include minimising dystocia, peri-parturient disease and teat damage. Separate or cull
cows that leak milk.
It is of interest that although there are many recommendations relating to prevention of coliform mastitis,
very few have been proven using interventions in farm trials. The exact usefulness of different measures
in different circumstances remains a matter of (often strong) opinion. Intervention studies involving
control methods are an area of current research and some improvement in the understanding of their
implementation may occur.
DRY PERIOD
The importance of the dry (non-lactating) period in the dynamics of intramammary infections in dairy
cattle has been studied over many decades (Neave et al., 1950; Oliver et al., 1962; Oliver and Michell,
1983; Smith et al., 1985; Oliver, 1988; Todhunter et al., 1991). Recently it has found that the dry period is
an important time for the establishment of new infections under UK conditions, and these can
subsequently account for over half of all gram-negative mastitis (Bradley and Green, 2000). The dry
period appears to be an area in which the practitioner can have great impact. Although dry cow
management has become rather more ‘fashionable’ in recent years, it is still frightening to see how poorly
many dry cows are managed. It is strongly recommended that the dry cows are made a central theme of
veterinary herd health and production.
i. Method of drying off
The act of administering antibiotics to a potentially sterile quarter is the first area of hazard and the need
for cleanliness in the procedure cannot be over-emphasised. Cleaning, disinfecting and drying the teat,
followed by stripping the quarter and at least two teat-end scrubs with spirit is the minimum
recommended prior to administration of an antibiotic tube and post dipping.
ii. Dry Cow Therapy
The selection of antibiotic dry cow therapy is an important element of a mastitis control scheme. The
efficacy of an intramammary antibiotic dry cow preparation with significant gram-negative spectrum
(Product A - 100mg Framycetin, 100mg Penethamate, 300mg Procaine Penicillin; Leo Red Dry Cow, Leo
Animal Health, UK) has recently been compared with a product with no gram-negative efficacy (Product
B - 600mg cloxacillin; Orbenin Extra DC, Pfizer Ltd, UK), (Bradley and Green, 2001). The efficacy of
both products was compared for control of coliform and non-coliform mastitis and for the ability to
control existing and new intramammary infections as measured by individual cow somatic cell counts.
Cows treated with Product A were significantly less likely to develop clinical E coli or coliform mastitis
during the dry period or the first 100 d of lactation, than cows treated with Product B. Cows treated with
Product A were no more likely to develop clinical mastitis due to a non-coliform organism than were
cows treated with Product B. There was no significant difference between the two groups as measured by
individual cow somatic cell count changes across the dry period. This study was the first to demonstrate
that selection of a dry cow intramammary preparation with extended gram-negative activity, could
influence the incidence of clinical coliform mastitis in the next lactation. Based on the reduction in
clinical coliform mastitis found in this study, the cost benefit was calculated at over 1000 Euros per year,
for a 100 cow herd. These findings should be one of the factors taken into account when selecting
products in herds known to have a significant incidence of coliform mastitis.
Alternatives to antibiotics for preventing dry period infections, such as teat sealants, are a possibility for
the future. Currently in use around the world, research findings in the UK suggest a future role for these
products in Europe (Huxley et al, 2002).
iii. Environment
“Clean, dry, cool, comfortable and inorganic”
It is common for dry cows to be housed in the oldest, poorest maintained buildings or kept on pasture
with little attention, a foolhardy strategy, when the dry period is probably critical not only in terms of
udder health, but also in other aspects of health and production. As a general rule, it is useful to ask the
question ‘is the dry cow environment at least as good as for the milking cows’. It is rare that any new
accommodation is built for dry cows but it is usually possible to make the best of existing facilities. These
are some issues that need to be addressed:
Comfort/housing type
Cubicles: Essentially as for lactating cows except width is probably more important. Are they
large enough for the size of a heavily pregnant cow? Can they be lengthened to suit large Holsteins (eg
2.44m x 1.22m) by using herring bone pattern or adapting layout of shed? Width may be effectively
increased by reducing the number of cubicles in a given space and by using flexible side partitions, such
as twisted rope. A low step (0.13m) may improve lying times, as can placing cubicles head to head where
possible. A slope of 1:20 is recommended for drainage, hence dryness, and a brisket board (1/4 of the
cubicle length back from head end) to encourage deposition of urine and faeces in the passageway!
Comfort is critical (see bedding).
Straw yards: Probably a better type of system than cubicles for foot health but almost always
worse for environmental mastitis pathogens. Recent work (Hughes, 1999) has indicated that below the
surface of even a recently bedded straw yard, warmth and moisture provide the ideal environment for
sustaining environmental bacteria. Don’t think that dry cows are unable to acquire new infections - they
are! Even using recommendations such as bedding up daily, cleaning out every 3-4 weeks and
maintaining low stocking densities (10m2 per cow bedded area and a cubic capacity of 15m3), infections
will still occur. Even in well managed straw yards, intramammary infections in the dry period are
inevitable.
Bedding types
Since deep straw is a problem for environmental infections, whether in yards or cubicles, what other
choices do we have?
Sawdust is an alternative commonly used with automatic slurry systems but has been associated with
increased infection rates with Klebsiella spp.
Sand or limestone, being inorganic materials, have been seen to sustain lower environmental bacterial
numbers. Anecdotally, sand has been found to be of great benefit in the UK and has been used in both
cubicles and indoor yards. It is easy to use and inexpensive, the main drawback is the deleterious effect on
mechanised tools (slurry systems and spreaders) in which bearings are easily worn. A cubicle bed of 5-10
cm of washed sand on a concrete base with a lip works well, and sand needs to be added only every 7
days, as long as any dung is removed daily from the cubicle ends. In a sand yard, daily dung removal is
also necessary and this becomes labour intensive with large dry cow groups. However, sand yards can
work very well, a minimum depth of 15-20cm is recommended.
Mats or mattresses with a small amount of straw or sawdust can also work well as long as dryness is
maintained. Comfort can be achieved from the mat or mattress and therefore deep straw (which maintains
warmth, moisture and bacteria) is unnecessary.
Hygiene
Dry cow accommodation passageways and loafing yards need to be kept as clean as possible with a
minimum of once daily scraping. It is essential to keep legs and feet clean to prevent soiling of the bedded
areas and contamination of teats. Similarly, while at pasture, it is important to prevent the poaching of
feeding and sheltering areas, particularly during wet periods. This necessitates either moving feeders or
laying hard-base feed areas, or moving pasture regularly. Principals are similar to those for lactating cows
and standards should not be lower.
Ventilation
Good ventilation is a key feature because it facilitates drying of the bedded areas and should therefore
reduce bacterial numbers. Dry cows are often housed in second rate conditions and it may be beneficial to
improve ventilation. This usually involves improving airflow through making low cost changes such as
opening ridge outlets, separating roof sheets, opening filled in sides and so on. When implementing these
changes, it is worth remembering that there should be no draughts introduced at cow level.
iv. Mixing of groups
It has been reported that housing pregnant heifers and dry cows together increases the risk of E coli
mastitis (Barkema and others 1998). This is something that can often be avoided through the use of
simple partitions, without huge building costs.
v. Leaking milk
Leaking of milk may be a risk factor for mastitis (Peeler, 2000). Problems with leaking milk may be
associated with dry cows which are over-fed before calving (rare), are in sight/sound of the parlour which
makes milk let down more likely, or are in the presence of calves (ie with recently calved cows). These
should be avoided if milk leakage is a problem on the unit. Otherwise segregating / culling offending
cows can be considered.
Have a look!
At the end of a veterinary health visit, it can be an eye-opening experience to look around the dry cows,
assessing their environment and condition. Once the importance of the dry period to environmental
mastitis control is conveyed, there is often good cooperation in carrying out some simple improvements.
vi. Cow resistance
Nutrition
Following reports that gram-negative pathogens may commonly be present in the udder for a prolonged
period before causing mastitis (Bradley and Green, 2000), it now seems likely that clinical manifestation
may occur following ‘stress’ situations or ‘trigger events’. To prevent such ‘trigger factors’, it is probably
important to consider E coli mastitis in terms of whole cow well-being. This theory is supported, for
example, by findings such as negative energy balance (van Werven 1999, Suriyasathaporn, et al) and
number of feed spaces per cow (Barkema and others, 1998) being related to the severity / incidence rate
of mastitis. Although all trigger events have probably not been identified, nutritional status is a leading
contender. Dry matter intakes, energy balance and mineral supplementation in the late dry (transition)
period, around calving and in early lactation are probably important in reducing clinical episodes of gramnegative mastitis. An energy density of the transition ration should be around 11 MJ/Kg dry matter, with a
dry matter intake of 10-12kg / cow / day. Vitamin E levels should be 1000-2000 iu / cow / day and
selenium 3-4 mg / cow / day in the transition diet, with up to double these levels fed in early lactation.
Any farm investigation of an environmental mastitis problem should, therefore, incorporate a full
assessment of feeding from the dry period to peak lactation, with emphasis on dry matter intake, energy
balance and minerals. If necessary external expertise should be sought. Other factors that could act as a
trigger for clinical mastitis may include overcrowding, a lack of escape routes, mixing of groups,
excessive walking distances and poor stockmanship.
vii. Vaccination
Recently a vaccine for coliform mastitis, based on a rough ( R ) mutant E coli (strain J5) has become
available in the UK, as it has been in the USA for some period. Use of the vaccine is associated with a
reduction in the number and severity of clinical coliform cases and it will have a role, alongside other
preventive measures, in the control of gram-negative mastitis. The cost benefit of the vaccine in the UK
will be heavily dependent on be the amount and severity of gram-negative mastitis, which is why efforts
should be made to assess this. It should be stressed that the vaccine is not a substitute for correct
management but should be used as an aid to further reduce the incidence and severity of gram-negative
mastitis.
RECURRENCE
As reported in the previous paper, recurrence and chronic infection have to be considered in relation to
gram-negative pathogens and in some herds can be of great significance. It is worth noting that high cell
count cows and herds occasionally result from gram-negative infections that should therefore be in the
differential diagnosis. Treatment of chronic, recurrent mastitis caused by these bacteria is often
unrewarding, even when they appear to be sensitive to the antibiotic in vitro. For this reason, culling cows
with chronic E coli or Klebsiella spp may be necessary, although cure during the dry period often occurs
and therefore drying off (the quarter or cow) is an alternative. It is also possible that these cows can act as
a reservoir for contagious spread.
SUMMARY
To improve control of gram negative-mastitis a series of steps are recommended;
1.
Quantify the problem, preferably by bacteriological examination of pre-treatment milk samples.
(Encourage proactive collection and freezing of pretreatment clinical mastitis samples).
2.
Ensure that the recognised control methods relating to calving box, lactating cow housing and milking
routine are in place.
3.
4.
Ensure dry cow management is good, including;
i.
method of drying off
ii.
dry cow therapy
iii.
the environment (beds, yards, atmosphere)
iv.
minimal mixing of groups
v.
good feeding practice, especially in the transition period
vi.
use of vaccination if likely to be cost beneficial
Be aware that trigger factors, such as negative energy balance and vitamin E and selenium levels, are
probably important and incorporate an assessment of feeding, and other factors which you consider
may affect cow well-being, into the investigation.
5.
Be aware that chronic gram-negative infections can occur and deal with them accordingly.
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