High TBC? Here’s how to track down the cause on your dairy farm

For many dairy farmers, TBC can be such a struggle to deal with, as any number of things can be behind the problem, writes independent farm adviser Brian Reidy

Wed, 22 Apr, 2026 - 14:43

Brian Reidy

I recently saw a social media post asking about investigating a TBC (total bacterial count) issue on a dairy farm, and felt the frustration of the poster — for many dairy farmers, it can be such a struggle to deal with, as it can be any number of things.

When a dairy farmer is dealing with a high TBC in milk, the goal is to systematically track down where bacteria are entering or multiplying in the system. It’s rarely just one cause — more often it’s a combination of hygiene, cooling, and equipment issues.

My advice is to first start with the basics: confirm the result. Occasionally, a high TBC reading can come from sampling or lab error, so repeating the test helps to rule that out before making any radical changes.

Next up, focus on milk cooling, because bacteria multiply rapidly if milk isn’t chilled quickly enough. Check the bulk tank is pulling milk down to ≤4C within a couple of hours after milking. Problems here often point to refrigeration faults, overloading the tank, or poor plate cooler performance.

Then move to equipment hygiene. The milking machine and bulk tank are the most common sources:

Inspect liners, clusters, pipes, and the bulk tank for milk residues or biofilm buildup;
Inspect the plate cooler and make sure it does not contain any perished rubber seals, etc;
Review the wash routine: water temperature (should start hot, between 70–77C), correct detergent levels, and proper circulation;
Has the detergent been changed lately?
Has an incorrect product been added in error?
Make sure jets are hitting all surfaces, and that wash cycles are long enough;
Check for worn rubberware — old liners can harbour bacteria even if they look clean;
Have you changed the type of liners you use?

After that, look at cow hygiene and milking routine. Dirty udders, poor teat preparation, or wet clusters can all introduce bacteria into the milk. Ensure:

Teats are clean and dry before milking;
Cracked sore teats or teats with warts can be very difficult to clean properly and harbour contamination;
Foremilk is stripped and abnormal milk is excluded;
Clusters are not being attached to dirty or wet teats.

Also consider environmental sources:

Dirty collecting yards, cubicles, or bedding (especially organic bedding like sawdust) can increase bacterial load;
Have you changed your bedding product recently?
Have you changed your supplier of bedding material?
Water quality matters too — contaminated wash water can undo an otherwise good cleaning routine;
Have you changed the source of your water?
Is your water from a well, council or group source?
Has there been any other issues, such as a drop in milk yield, lower feed consumption or other groups of animals getting sick. Such issues can indicate a water contamination issue.

A useful approach is to take samples from each stage of the process:

Milk straight from the cow;
Milk in the cluster;
Milk entering the bulk tank;
Milk from the bulk tank.

Comparing these helps pinpoint where contamination is happening.

Also, have a chat with your milk buyer to make sure there is no issue with the bulk tank collection that you or they are not aware of. Ask suppliers on the same collection route if they have any TBC issues at the moment, too.

If the issue persists, involving a specialist — like a dairy adviser or vet — can help. They may recommend detailed testing, including thermoduric bacteria checks or a full milking machine audit.

It is a process of elimination:

Cooling → cleaning → cows → environment → equipment condition.

The sooner you narrow it down, the easier it is to bring TBC back within limits.