27 Aug 2017
Dry cow therapy (DCT) is an essential part of a dairy farmer’s routine to ensure the health and
welfare of his/her cows. The dry cow period is a high risk time for acquisition of new bacterial infections.
While there is no evidence of change in resistance patterns in animals or humans arising due to
antibiotic use in intramammary preparations, the current concerns over the use of antibiotics and
possible implications with antimicrobial resistance mean it is timely to review the current practice to
treat all cows at the end of lactation to both prevent new infections and treat any existing infections.
It is timely also to review the current situation in dairy farming particularly with regards the
incidence of intra-mammary infections, monitoring tools and the availability of products that were
not available when recommendations such as the Five Point Plan were developed in the 1960s. The
Five Point Plan recommended the use of antibiotics at the end of lactation in all dairy cows to treat
existing infections and prevent new infections occurring during the risk periods when cows were
non- lactating. Current RUMA guidelines recommend that there should be a strategy for drying off
policies at the individual cow level.These Factors to consider when contemplating selective dry cow antibiotic use
Infection status of the herd
The infection status of the herd is a factor to consider when deciding on screening options and
setting criteria or levels to use for selection of cows. Herds can have varying levels of bacteria e.g.
Staphylococcus aureus, Steptococcus uberis. In such circumstances, it is advisable to screen cows by
routine bacteriological monitoring of clinical cases or
selection of cows at drying off or
bulk milk sampling at regular intervals and using bulk milk bacteriology or PCR (Polymerase
Chain Reaction) to detect bacteria such as Streptococcus agalactiae. Streptococcus
agalactiae rarely survives for long periods outside the udder and detection of this bacterium
in a bulk milk sample using PCR indicates infections within the herd.
Herd management
Recent work on selective dry cow strategies – no dry cow therapy, antibiotic therapy and internal
teat sealants – has been carried out on both organic and conventional herds (Berry and Hillerton,
2001 a and b and Berry et al 2004). Statistical analysis indicated that herd factors and management
(including conventional or organic or low somatic cell count) was not a significant risk. All herds are
at similar risk to new infections during the dry period with the major risk factor being if cows were
left untreated during the dry period.
Currently organic herds can use internal teat sealants in all cows at the start of the dry period
and apply for a derogation to use antibiotics at the start of the dry period on cows considered to be
infected. Usually an elevated somatic cell count is considered to indicate an infection with anything
over 200,000 cells per ml considered as indicating an infected cow.
Hygiene at drying off
Whatever product is used at drying off an aseptic technique is essential. Even those products
containing antibiotics do not protect against all bacteria. Anecdotal and published cases of
infections in the dry period attributed to poor infusion technique are available (Milnes and Platter,
2003.
Treatment at cow or quarter level
There is some discussion as to whether treatment should be at the whole udder or quarter level
but most evidence supports the fact that if one quarter is at risk of infection there is a higher risk in
the other three quarters. Thus any dry cow strategy should be applied at the cow not the quarter
level.
Dry period length
Previous work has demonstrated that a dry period longer than the anticipated length of activity
of the dry cow antibiotic is a risk factor for more intramammary infections and clinical incidence in
the next lactation (Natzke et al., 1975, Rindsig et al., 1978, Bradley and Green, 2001, Roberts at al.,
2003, Berry and Hillerton 2002, Berry and Hillerton 2007). Thus, if using an antibiotic at drying off,
the use of a teat sealant in addition to DCT to provide protection for the period beyond the activity
of the dry cow antibiotic is advisable.
Infection status at drying off
The internal teat sealants available in the UK claim no antimicrobial activity and the
recommendation is to use these products in low somatic cell count uninfected quarters, when used
alone. Internal teat sealants have been used in cows with quarters infected at drying off with no
adverse effects but cure rates are low and more likely attributable to self-cure rather than
therapeutic activity of the internal teat sealant.
Selection criteria to use to decide on infection status at the cow level
It is generally accepted that a somatic cell count below 200,000 cells per ml at the cow level is
indicative of a low probability of being infected (IDF Bulletin 321, IDF Guide to use and interpretation
of cell counts 2013). It is also recommended that more than one somatic cell count is used to
determine infection status (IDF Bulletin 321, IDF Guide to use and interpretation of cell counts 2013).
Using this cell count as a guide along with examination of the udder and teats for any abnormal
changes should provide an indicator to the infection status of the udder. For practical purposes
selection criteria may use the somatic cell count history and clinical mastitis data for the lactation
prior to the dry period (O’Rourke, 2005). Other recognised tests for the detection of subclinical
mastitis may also be used e.g. conductivity. It is recommended that cows should have had no clinical
cases and all somatic cell counts for that lactation should have been less than 200,000 cells per ml if
internal teat sealant is to be used alone. Appendix one in the IDF Bulletin 321 gives examples of the
quarter cell counts that obtained within quarters at varying cow cell count levels. Registration work
for OrbeSeal TM detected no infections due to major pathogens in quarters, present at both drying
off and calving, using the criteria of all cell counts less than 200,000 cells per ml and no clinical
infections in the relevant lactation.
Antibiotic choice
There are a range of antibiotics available for use in current dry cow products and only one
product is currently available that contains a Critically Important Antibiotic (CIA) cefquinome, a
fourth generation cephalosporin. This antibiotic is only available for animal treatment.
Options for treatment at the start of the dry cow period
Use the monitoring results to decide the appropriate treatment for each cow you are drying off
do nothing and monitor closely for the potential development of mastitis (a health and
welfare risk for the cow)
use an internal teat sealant
use dry cow antibiotics
use both an internal teat sealant and antibiotic.
Each farm should have a strategy at the cow level for the dry period and this should be discussed
with your vet and reviewed regularly.
Individual farm strategies
These should take account of various risk factors including
bulk milk somatic cell count value,
routine screening for bacteria including Streptococcus agalactiae,
if individual cow somatic cell counts are carried out
purchase history of the cows.
Each farm must be able to identify cows with intra mammary infections from those that are
uninfected. Ideally this would be by using bacteriology but this can be time consuming and
expensive. A good indicator of intra mammary infection status is using somatic cell counts. It is
generally accepted that for on farm management a somatic cell count for the cow level of above
200,000 cells per ml would indicate infection is present in one or more quarters. It is recommended
to use more than one somatic cell count to obtain a reliable result on intra mammary infection
status (at least three and preferably for the whole lactation). Clinical mastitis history is also a good
indicator of risk of intra mammary infection.
Ideally cows that would be suitable for an internal teat sealant alone would have had
somatic cell counts below 200,000 cells per ml for all cell counts
no clinical cases of mastitis
no obvious teat lesions at the time of drying off.
It is recommended to carry out routine bacteriology on clinical cases and screen bulk milk
samples at regular intervals for Streptococcus agalactiae, which is very contagious and can cause
intra mammary cases, without extremely elevated somatic cell counts. Streptococcus agalactiae is
the most frequent cause of neonatal death in man but these cases do not usually arise from bovine
infections. However, reports from the Nordic countries have highlighted an increase in the
prevalence of Streptococcus agalactiae cases in dairy cows. While this increase will be
multifactorial, contributing factors may be not identifying all cases with routine monitoring and use
of selective antibiotics at the end of the dry period in Nordic countries.
Remember, antibiotics should be used as little as possible and as much as necessary.
