Mastitis: some lessons from the past - Veterinary Practice
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InFocus

Mastitis: some lessons from the past

Richard Gard traces the development of efforts to control mastitis but finds that there is still a long way to go…

MANY veterinary surgeons in
cattle practice have good reason
to be thankful for the National
Institute for Research in Dairying
and the many collaborations and
joint meetings with the BCVA on
mastitis control.

People who have copies of
important publications, including
Control of Bovine Mastitis (1971) or
Seminar on Mastitis Control (1975) or
Machine Milking (1977) or Mastitis
Control and Herd
Management
(1980)
may nd it worthwhile
to blow off the dust
and reconsider the
fundamentals of udder
disease. Much of the
early work has direct relevance to the
application of mastitis control today.

Clearly, the disease and the herds
have changed. The early research was
set against a fall in the number of milk
producers (196,000 in 1950 to 61,000
in 1979) with the same number of
dairy cows (3.3 million in 1979 and
3.2 million in 1960) and a subsequent
increase in herd size (20 to 56 cows
with an increase of three cows per
year).

Today there are fewer than 10,000
dairy herds with 1.8 million cows,
giving an average herd size of about
180 cows; yields are commonly more
than twice the average in the 1970s.

The early researchers considered
that increased yield and increasing herd
size was expected to result in a higher
prevalence of mastitis. However, a
reduction in herd subclinical mastitis
levels was already being recognised.

The NIRD Mastitis Field
Experiments 1, 2 and 3 were truly
ground-breaking and the findings
from the 30 herds involved led to the
development of the fundamentals of
mastitis control that have lasted for
40 years. Those fundamentals are now
being reassessed.

A major impact was that over half
the cows were infected with pathogens.
These were detected by plating out
milk samples from individual quarters.
Nearly 30% of the quarters were
infected.

These studies led to the promotion
of the idea that as over half the herd
was infected it was important to treat
every quarter of every cow at drying-
off with an antibiotic that would
counter resistant staphylococci.

The development of penicillin
resistance was a considerable concern.
The big point, that was emphasised
time and again, was that it was
necessary not only to treat existing
infections but also to prevent new
infections during the dry period. Dry
cow therapy products became the norm thereafter, rather than the option
of blitz treatment of the whole herd
during lactation.

It was also recognised that
intramammary antibiotics needed to
reach the site of infection in order to
lyse the bacteria and that some bacteria
were only vulnerable when they were
dividing. The conditions for bacterial
reproduction may be changed when
the cow is dry or lactating but keeping
the antibiotic in potential contact with the site of infection for the longest
practical time was the aim of the
pharmacokinetics.

Clinical therapy was always in doubt
as an effective means of eliminating
infections but the incidence was
subdued and the milk returned to a
saleable state. Subsequent outbreaks
of mastitis as a consequence of
inadequate nutrition, linked to
production, have emphasised the
need to understand more fully the
relationship of immune response with
supportive therapy.

The combined challenges of
milk production, automation and
transfer of infection are different
today and greater practical research
and understanding still need to be
converted into application.

Persistent offenders

The role of the individual infected cow,
as a risk to the rest of the herd, was
always recognised. A history of clinical
mastitis led to the recognition of
“persistent offenders” and in the early
experiments cows with eight or more
attacks of clinical mastitis in a lactation
were culled at drying-off.

The whole topic of potential risk to
other cows led to recommendations
for the farmer to manage persistent
offenders in ways that would reduce
the spread of infection. This has
arguably been the least effective aspect
of mastitis control.

Early detection of infection
continues to be the subject of
research with automatic analysis of
the milk being offered in increasingly
sophisticated ways.

The means of transfer of infection
during the milking process led to much
more emphasis on the role of the
milking machine. Early on, a 10-fold
difference in the rate of new infection
was recorded between herds. Reducing
skin contamination, preventing the
colonisation of streak canals and
repairing teat lesions or abrasions were considered fundamental and became
the role of teat dipping.

All the studies emphasised the
need to reduce bacteria on the teat.
Pathogens emanating from dung, soil
and dirty water were considered “to be
much less influenced by conventional
hygiene”.

The new tool that followed the
early work was cell counting. Looking
through the bulk milk cell count results
for herds tested in the 1970s it is
interesting that there was considerable
variation. The national picture was that
some 10% of herds averaged over 1
million cells per ml and fewer than 3%
of herds had counts under 200,000.

The month to month data show a
remarkable consistency with some of
the low cell count herds. One of the
issues with the smaller herds was a
rise in cell count during the summer.
Typically, many herds were autumn
calving and cell counts rose at the end
of lactation.

Veterinary surgeons started to
receive individual farm data by request
and 30 years ago 74 practices received
the data for 1,859 herds (less than 5%
of the herds).

The cell count figures gave a
rational basis to discuss the situation
with mastitis in a herd. Veterinary
surgeons were said to need to change
from being the sole supplier of
antibiotics and providing an emergency
treatment service, to giving attention to
subclinical mastitis.

It was said that the veterinarian
“needs to monitor the progress in
mastitis control in his clients’ herds and
have a systematic way of dealing with
the problems”.

A “basic” mastitis control routine
was recommended for all herds – teat
dipping, dry cow therapy, examine
foremilk, treat clinical cases promptly,
cull cows with more than five cases in a
lactation, test the milking machine and
correct any faults and maintain a high
standard of husbandry, housing and
management.

The main problem for the vet
was believed to be “getting farmers
to follow all aspects of the routine
faithfully all the time”.

There was recognition that a poor
standard of husbandry, housing and
management existed on many farms
and that this would not be improved
by the ever increasing number of cows,
being cared for by fewer people.

Subclinical cases

The trigger for veterinary action
was expected to move from an
increasing incidence of clinical mastitis
to advising on the intricacies of
subclinical mastitis. Individual quarter
cell count readings have led to a greater
understanding at farm level of the
importance of controlling levels that
influence income. Great technical work
is ongoing to make it easier to interpret
the data.

The other big development has to
be with the application and design
of the milking machine. Fluctuating
vacuum at the teat end was recognised
as an issue related to the propulsion
of bacteria through the teat into the
udder.

Baffles were introduced to reduce
this but the emphasis was always to
reduce the pathogens on the teat in the first place.

Today, the farmer appears to be most
interested in nutrition and automation.
However, the early understanding of
the action of bacterial invasiveness and
immune response is clearly a veterinary
role to be updated into active cow
management.

By looking back to see forwards, it
does seem likely that understanding
udder disease will require positive
development for many years to come.

  • The 2014 British Mastitis
    Conference will be held on 14th
    November at Worcester.

Note: Richard Gard was technical
officer for a mastitis control
programme involving 700 herds from
1970 to 1974.

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