Reducing Somatic Cell Counts

Considerable success has been achieved in reducing the Somatic Cell Counts (SCCs) in bulk milk samples in previous years in Northern Ireland.  However data from National Milk Records recorded herds shows that there is a clear rising trend in cell counts associated with stage of lactation, lactation number and herd size.  Northern Ireland milk quality statistics also show an increase in somatic cell counts in 2006 compared with recent years.

The concentration of somatic cells in the milk is directly related to infection of the udder.  If the somatic cell count is high, but no obvious signs of the infection, the cow has sub-clinical mastitis.  However the reverse can also be true where a cow can have a clinical case of mastitis with obvious signs (clots in the milk, hard quarter etc) but her SCC can remain relatively low.  Therefore, in the day to day management of the dairy herd, the sub-clinical infection status of the herd can be monitored effectively by observing the SCC of bulk tank milk or individual cow samples.

The cost of sub-clinical mastitis and high somatic cell counts can be substantial.  As the cell count in the bulk milk sample rises, it is directly related to more quarters of more cows being infected.  This may result in cell levels of 400,000-800,000 cells/ml and such levels are a concern for three main reasons: -

1) the cost of a penalty for producing milk with a high bulk tank SCC (this will vary depending on litres produced and on milk purchaser)

2) the cost of reduced milk yields due to the sub-clinical infections in the herd as highlighted in the table below.

Yield loss due to increased bulk tank SCC

Example of a 100 cow herd with an average yield of 6,000 litres per cow

* Milk yield drops by 2.5 percent for every increase in SCC of 100,000 above the base figure 200,000/ml (Blowey & Edmondson, 1995)

3) the cost of replacing individual cows with consistently high cell counts.

These costs will be further increased by the expenditure of treating any clinical cases of mastitis, the loss of discarded milk and lower animal milk yields.

Milk recording is invaluable for identifying cows with sub-clinical mastitis.  While these cows do not exhibit outward signs of mastitis, a small number can have a considerable effect on herd SCC.  Typically 15-20 percent of cows have sub-clinical mastitis during the year with SCCs exceeding 250,000 cells/ml.  In a herd with a low incidence of mastitis, bulk tank samples should be less than 150,000 cells/ml.  Remember milk with a SCC of greater than 400,000 cells/ml is not permitted to enter the food chain.

Individual high SCC recordings can be due to a particular problem.  It is recommended to assess individual / cows SCCs over several months to identify trends and underlying issues.

The Five Point Plan for reducing SCCs and cases of mastitis is a long established scheme and will be familiar to the majority of dairy farmers.  However the five key elements are still important today:

It is essential to treat all cases quickly to prevent spread of the infection.  Record all cases to establish the level of clinical mastitis and to determine if there is a pattern.  

Pre-milking disinfection can reduce the incidence of environmental mastitis by up to 50 percent.  Post-milking teat dipping, if correctly applied, can reduce the incidence of new cases of contagious mastitis by up to 50 percent.

Occasionally treatment aimed at keeping a problem cow in the herd fail or are simply not the best option as she can impact on the whole herd.  In these cases there may be no option but to cull the cow taking short term loss for long term profitable of the herd.

Proper management of the dry cow and in-calf heifer is the most effective strategy for the control of high cell counts.  To be effective in controlling mastitis a whole herd approach to dry cow therapy is essential.  Consult your local vet to discuss the most appropriate and effective program for your herd.

The milking parlour provides the interface between the cow and the bulk milk tank and should be maintained regularly.  Short term faults of the milking equipment have an immediate disruptive effect on cow performance and all other farm work.  Long-term milking equipment malfunctions such as excessive liner slippage or fluctuating vacuum levels can lead to irreversible teat damage and high levels of mastitis infection.

The Animal Health Challenge for dairy farmers covers mastitis, and other animal health issues, in greater detail and is open to all dairy farmers to apply.  For further details please contact your local Dairy Development Adviser.