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The current discussion regarding lowering the legal somatic cell count (SCC) limit to 400,000 cells/ml has, if nothing else, stimulated more questions from producers about why their counts are higher than they would like.
Recently I received a call from a producer whose bulk tank SCC (BTSCC) typically runs solidly below 200,000. But over the last few months, it has slowly crept up to just under 300,000. During this time, there was little change in the number of clinical mastitis cases being treated. Routine monthly bulk tank bacterial screens showed traces of Staph. aureus, low levels of other Staph. species, low levels of coliforms and moderate levels of environmental Streps. This was fairly typical for what this producer saw historically.
His local veterinarian and milking machine dealer had reviewed the parlor procedures and milking machine function and they appeared to be in control as well. Freestall management had been reviewed and it was concluded that there had been no significant changes. They were at a bit of a loss as to where to look next.
When analyzing BTSCC problems, there are some guidelines that, while not set in stone, will generally point you in the right direction. First, the BTSCC is a reflection of the number of cows in your herd with subclinical infections. These are infected quarters that, by definition, have what appears to be normal milk but elevated SCC.
Second, many of the mastitis-causing organisms we deal with are related more to subclinical infections than to clinical infections. In other words, if your BTSCC has gone up, chances are you have somehow created an increase in individual cows with high counts even if there is not an increase in clinical cases.
To get a quick idea of which cows are contributing to an elevated BTSCC, you need to have individual SCC counts. I use 200,000 cells/ml as a cutoff when analyzing individual cow patterns. If they are above 200,000 cells/ml, I assume they have a subclinical infection. If they are below 200,000 cells/ml, I assume they are uninfected.
Using this guideline, I look at each cow’s record and compare each month’s SCC to the previous month. I then group them into three buckets:
- Cows that have counts above 200,000 cells/ml for both months. These are considered chronically infected cows.
- Cows that are high in the current month but were low the month before. These are the new infections.
- Cows that have high counts on their first test after freshening. These are cows that probably freshened with a problem.
When we did this exercise with this herd, it was evident that BTSCC had elevated as the number of chronic cows increased. Further-more, many of the cows had high first-test SCCs. This pattern seemed to start about four months ago.
Discussion resulted in a review of dryoff procedures as well as close-up dry cow and fresh cow bedding management. Six to seven months ago, the individual responsible for dry-treating cows had changed how cows were prepped prior to dry treatment. This was resulting in environmental Strep infections.
While this may not be the only thing contributing to this herd’s current BTSCC levels, early indications are that correcting the situation has led to a drastic drop in high first-test SCCs. Unfortunately, it will take a while to correct all the chronic infections that were created.