A Cell Count Contributors Table is a very useful tool to understand how individual cows and/or groups of cows are contributing to the overall Bulk Milk Cell Count (BMCC) of a herd.

It is also highly useful to help deal with herds trying to achieve a particular BMCC level (e.g. for premium payments).

We regularly hear of farms either culling or withholding high cell count cows from the vat, and then seeing little or no change in the BMCC.

There are a number of reasons why this might occur, but three factors are likely to be very significant.

Firstly, the worst cows in terms of them having the highest Individual Cow Cell Count (ICCC) may well not be the worst cows in terms of contribution to the overall BMCC.

A cow’s contribution to the BMCC is not just about how high her cell count is; it is actually a function of both her current ICCC and also the volume of milk she is contributing to the vat.

The pattern of this contribution may also have an effect as there may be a larger number of cows with a moderately high ICCC rather than a small number of cows with a very high ICCC creating a problem.

Secondly, a cow’s ICCC is not a static number – a cow’s cell count can change from day to day, and even from hour to hour.

A cow that was tested on one day may have a similar ICCC again the next day, or she could have a quite different ICCC the next day simply as a result of both natural biological variation and the cow’s immune system responding to the varying levels of challenge in the udder.

If enough cows change their ICCC, then the overall BMCC will change as a result.

The third likely factor is that mastitis infections in a herd are a dynamic and fluid situation, thereby constantly changing.

Over any period of time, previously uninfected cows are becoming infected, and some infected cows are being cured, either by treatment or by self-cure.

It is the rate at which these changes are occurring which can cause significant changes in which cows are contributing most to the BMCC at any given time, and if this rate of dynamic change is high, then culling or withholding cows from the vat may seem to have little or no effect, simply because other cows have become infected over that time and have become significant contributors to the BMCC.

A Cell Count Contributors Table tells us how each cow is contributing to the overall BMCC at the time of testing.

Skilled analysis of these tables helps understand the dynamics of mastitis in a herd and formulate the appropriate response. It also helps to explain why some farms see little or no effect when they simply withhold the highest cell count cows.

To obtain a Cell Count Contributors Table for your herd, just contact the Dairy Focus office and we will organise to obtain the herd test data, produce the table, and then talk you through what it means for your herd.

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