The following sections give a summary of both clinical and subclinical (increased somatic cell count) data for the UK in the last 10-15 years. A review of developments in Dairy Udder Health can be read in the most recent Cattle Health and Welfare Group (CHAWG) Report published in November 2020.
The most recent prospective national survey was carried out across England and Wales in 2004-05 and quantified the UK situation with regard to the pathogens involved in both clinical and sub-clinical disease (Bradley et al 2007). This work was published in the Veterinary Record, and a copy of the full paper can be requested here.
Bacteriology results obtained from 480 clinical mastitis samples submitted for culture revealed Streptococcus uberis and Escherichia coli to be the most commonly isolated organisms, accounting for 23.5% and 19.8% of cases respectively. Bacteriology results from 464 sub-clinical mastitis samples (i.e. samples from high somatic cell count cows) collected during this survey, showed 13.8% cultured S. uberis and 5.2% cultured Staphylococcus aureus although almost 40% returned a diagnosis of no growth, indicating how difficult isolation of major mastitis pathogens can be from persistently infected cases. In conclusion, the survey carried out by Bradley et al showed that environmental pathogens (pathogens predominating in the environment) tended to predominate but contagious pathogens (pathogens spreading from cow to cow) remained an important issue in some herds; a clear shift away from the UK situation 50 years ago.
More recent data published at the British Mastitis Conference in 2013 presented information regarding the aetiology (causes) of mastitis from 6,005 samples from 991 submissions to the QMMS laboratory (www.qmms.co.uk), coming from over 500 farms throughout the UK of which 43.8% were from clinical cases. Environmental pathogens predominated, with E. coli diagnosed in more than 19% of clinical, and 9% of subclinical submissions. Streptococcus uberis was diagnosed in 17% of clinical, and 14% of subclinical samples, whilst Staphylococcus aureus was isolated from 6% of clinical, and just over 9% of subclinical submissions. Importantly, more than 100 different bacterial species were isolated, including more unusual isolates such as Salmonella spp. and Listeria spp., making the point that the causes of bovine mastitis in the UK are extremely diverse and encompass a huge range of opportunistic environmental pathogens. Interestingly, the proportion of samples with apparent 'no growth' after 72 hours incubation was just 12% (clinical) and 10% (subclinical submissions), highlighting that well-collected samples with a detailed diagnostic approach can yield very useful information.
The most recent clinical mastitis data from the period following national implementation of the Dairy Mastitis Control Plan between 2009 and 2017 is summarised below. In addition, other sources report clinical mastitis incidence data, although it must be remembered that the last national prospective study remains the work by Bradley et al (published in 2007), from a large cohort of herds in England and Wales looked at in 2004-05.
Importantly, it must be remembered that average figures are often reported on small numbers of well-recorded herds and clinical mastitis data remains poorly reported by many herds in the UK, with both under-reporting (e.g. first case only) and over-reporting (e.g. treatments for subclinical infections reported as clinical events) common. Variation also exists within herds depending on the source of data for analysis, e.g. on farm software data capture, data capture by Third Party etc.
AHDB Sentinel Herd Data
The AHDB Sentinel Herds project involves collating data from sentinel farms to monitor trends in mastitis. A geographically representative population of approximately 100 “Sentinel Herds” was recruited in 2016, with the requirements 1) reliable electronic recording of clinical mastitis and 2) preferably monthly Individual Cow Somatic Cell Count recording. Funding currently covers data collation and analysis from these herds until December 2020. Posters reporting on data from 2016, 2017, 2018, 2019 and 2020 have been presented at the British Mastitis Conference.
Clinical Mastitis Data: Mastitis Control Plan (2013-16)
Data from up to 231 herds which reported on the impact of the Mastitis Control Plan between 2013 and 2016 were collated and analysed. The average rate of clinical mastitis fell by 20% in these herds, from 44 cases per 100 cows/year to 35 cases per 100 cows/year. Data were presented to the British Mastitis Conference in 2016 and a copy of the poster presentation is available here.
For herds that engage with the Plan and report clinical mastitis data, progress can be readily tracked. An example of a herd that began the Dairy Mastitis Control Plan in 2012 is shown below and clearly shows the impact of a sustained and farm-specific approach, reducing the overall incidence rate of clinical mastitis from 70-80 cases per 100 cows/year to ~30 cases per 100 cows/year during a 4-year period:
An Illustration of the Clinical Mastitis Rate in a UK Dairy Herd over a 5-year Period compared to a target incidence rate (red line) of 0.25 cases per cow/year or 25 cases per 100 cows/year (source TotalVet/QMMS)
Clinical Mastitis Data: Mastitis Control Plan (2009-2012)
The final report from the first three years of the national Mastitis Control Plan is available to download. A total of 954 herds were enrolled on the Plan between 2009 and 2012 but the proportion of herds submitted to the full DMCP process with little or no clinical mastitis data initially was approximately 40%, and there remains a huge challenge to encourage reporting of clinical mastitis on farm. Farmers, veterinary surgeons and consultants were encouraged and supported to provide clinical mastitis data for the DMCP during this period, and more robust data was therefore available in these herds at this time.
The variation in clinical mastitis incidence rate at the beginning of Plan implementation for 841 of these herds is shown below; the median (middle herd) clinical mastitis rate was just over 50 cases per 100 cows/year:
Distribution of incidence rate of clinical mastitis (IRCM; cases per 100 cow-years) at day zero for herds enrolled to the DMCP between 2009 and 2012
Herds were then monitored by requesting data every 12 months from Plan Deliverers engaged with these herds and changes in the incidence rate of cows affected (IRCA) with clinical mastitis and the incidence rate of clinical mastitis (IRCM) evaluated.
Overall in these herds, the IRCA fell by an average of 3%, with herds complying with more than two-thirds of the Mastitis Control Plan priorities listed for their farm seeing a reduction of 10%. However, the IRCM remained relatively unchanged in these herds, and for high compliance herds, the IRCM actually increased. This is likely be a result of increased and improved recording of clinical mastitis - raising awareness may have increased this type of recording, meaning herds that engage well with the Plan appear to do worse in terms of clinical mastitis in the short term as they report it much better. This effect was not apparent in the low compliance herds, who either didn't report it at all, or who did report clinical mastitis but then stopped.
Clinical Mastitis Data: Overviews from Other Sources
Data from other sources highlight downward trends in the incidence rate of clinical mastitis data for those herds that report it.
Both The Kite Health Monitor (www.kiteconsulting.com) and the Kingshay Dairy Costings Focus Annual Report show downward trends within their clients' data over the past 5 years, with figures for 2016 putting the incidence rate of clinical mastitis at 36 and 49 cases per 100 cows/year respectively.
Data uploaded to the TotalVet database (www.total-vet.co.uk) reports the average clinical mastitis rate at 24 cases per 100 cows/year (below), but this is clearly hampered by >25% herds in the database that do not report clinical mastitis events in their on-farm software.
The most recent prospective national survey was carried out across England and Wales in 2004-05 and quantified the UK situation with regard to clinical disease incidence and the pathogens involved in both clinical and sub-clinical disease. This work was published in the Veterinary Record, and a copy of the full paper can be requested here.
Of the 125 dairy herds surveyed, 97 returned samples and data to enable analysis to be performed. The incidence rate of clinical mastitis cases (cases per 100 cows per year) from 90 dairy herds across England and Wales is shown below, with almost a quarter of herds reporting greater than 100 cases per 100 cows per year. The study concluded that the incidence of clinical mastitis in dairy herds in England and Wales at this time was somewhere between 47 and 65 cases per 100 cows/year; higher than previously thought.
As a broad rule of thumb, for every 100,000 cells/ml increase in bulk milk somatic cell count (BMSCC), approximately 8 to 12% of the herd is likely to be infected - i.e. a dairy herd with a BMSCC of 200,000 cells/ml would be expected to have approximately 20% of the cows infected at any one time. Cell counts are therefore a good proxy for intra-mammary infection, and despite other factors that influence cell count (such as age of the cow and stage of lactation), provide extremely useful information on likely infection status.
A number of UK sources report SCC information, and some of which is summarised in this section. Milk recording information is often more readily available for UK dairy herds than clinical mastitis data, and therefore SCC data is reported and analysed to a greater degree. However, it must be remembered that in low SCC herds, clinical mastitis data becomes increasingly important to measure as an outcome of udder health.
Data are produced by AHDB on the hygienic quality of milk including somatic cell count (SCC), and a summary of the UK SCC situation is shown below, highlighting the overall reduction in national herd average SCC since 2010.
An illustration of the UK herd somatic cell count for the years 2010 - 2020 (source: AHDB )
AHDB Sentinel Herd Data
The AHDB Sentinel Herds project involves collating data from sentinel farms to monitor trends in mastitis. A geographically representative population of approximately 100 “Sentinel Herds” was recruited in 2016, with the requirements 1) reliable electronic recording of clinical mastitis and 2) preferably monthly Individual Cow Somatic Cell Count recording. Funding currently covers data collation and analysis from these herds until December 2019. Posters reporting on data from 2016, 2017, 2018, 2019 and 2020 have been presented at the British Mastitis Conference.
SCC Data: Mastitis Control Plan (2013-16)
Data from up to 231 herds which reported on the impact of the Mastitis Control Plan between 2013 and 2016 were collated and analysed. There was an improvement in somatic cell count over the four years of monitoring. Over three years, the average bulk milk somatic cell count dropped by 24,000 cells/ml to 176,000 cells/ml, a decrease of 12%. The proportion of herds above 200,000 cells/ml and the number of chronically infected cows (i.e. 2 of the last 3 recordings >200,000 cells/ml) fell by 9.7% and 16.1% respectively. A copy of the data presented to the British Mastitis Conference is available here.
SCC Data: Mastitis Control Plan (2009-12)
The final report from the first three years of the national Mastitis Control Plan is available to download and view here. A total of 954 herds were enrolled on the Plan between 2009 and 2012. Information regarding SCC for 841 of these herds was available at the beginning of the Plan implementation process and the bulk milk SCC for these herds is shown below. Compared with reporting of clinical mastitis data, herds that did not routinely milk record and therefore had no somatic cell count data were far less common; <5% of herds submitted for the DMCP in this period had no or little SCC data.
Distribution of bulk milk somatic cell count at day zero for herds enrolled to the DMCP between 2009 and 2012
The average reduction in BMSCC across these herds during this Plan period was very small; however there was an average reduction of 6% in the proportion of cows with a SCC>200,000 cells/ml, and an average reduction of 5% in the proportion of chronic high SCC cows. For high Plan compliance herds (herds implementing more than two-thirds of the farm-specific recommendations), the average reductions were much larger - 13% fewer infected cows and 16% fewer chronic cows. Importantly, improvements in SCC in these high compliance Plan herds was not brought about simply by removing infected cows - rates of new infection were also reduced. In high compliance herds, the rate of new infection in lactation (i.e. the proportion of cows moving from <200,000 cells/ml to >200,000 cells/ml between milk recordings) reduced by 11%, In high compliance herds, the rate of dry period infection (i.e. the proportion of cows >200,000 cells/ml at the first milk recording in lactation) reduced by more than 15%.
Importantly, the impact of the Plan on SCC parameters varied according to the initial herd diagnosis. For example, the impact of a farm DMCP on the rate of new dry period infections was most marked in herds in which the dry period was identified as an issue - and in these herds with very good compliance, the reduction in new dry period infections averaged 18%.
SCC Data: Overviews from Other Sources
A summary of individual cow SCC data from a variety of sources has been published as part of the most recent Cattle Health and Welfare Group (CHAWG) Report, including data from National Milk Records (NMR) in the KPI report for 500 Holstein-Friesian herds in 2020, data from the Cattle Information Service (CIS), data from QMMS Ltd. and data from TotalVet. This data from the CHAWG report is shown in the table below.
Percentage of somatic cell count samples from recorded dairy herds, by different criteria (source: CHAWG Report 2020)
This data continues to highlight the importance of the dry period as a risk period for acquiring infection as measured by SCC. The dry period new infection rate (i.e. proportion of cows dried off at <200,000 cells/ml that are >200,000 cells/ml at the first milk recording in lactation) is reported as 10-16% across the data sources above, and this will impact on the apparent dry period cure rate (i.e. proportion of cows dried off at >200,000 cells/ml that are <200,000 cells/ml at the first milk recording in lactation) which continues to be reported at around 75%.
Importantly, there is much variation in these individual cow SCC parameters, for example the variation in dry period cure rate for a cohort of 650 herds uploaded to the TotalVet database which is shown below. This highlights the importance of understanding the pattern of mastitis infection on farm, and the role of the DMCP in targeting control measures in a farm-specific manner.
Variation in herd average dry period cure rate (source: TotalVet/QMMS)