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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.

Data produced by AHDB on the hygienic quality of milk including somatic cell count (SCC) can be found here, and a summary of the UK SCC situation is shown below, highlighting the overall reduction in national herd average SCC over the years 2009 to 2017, and the first six months of 2018.

 

An illustration of the UK herd somatic cell count for the years 2009 - 2018 (source: AHDB Dairy)

 

The most recent subclinical mastitis (SCC) data from the period since national implementation of the Dairy Mastitis Control Plan between 2009 and 2017 is summarised below. Other sources report SCC information, and these are also summarised. Milk recording information is often more readily available for UK dairy herds compared with 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.

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 2016 data and 2017 data 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 2017, 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 2018)

 

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)