Guide
Lowering somatic cell count in your dairy herd
Where a high bulk tank SCC comes from, how to trace it to the individual animals causing it, and what to do about the chronic ones.
What the number means
Somatic cells are mostly white blood cells, and their concentration rises when the udder is fighting infection. Bulk tank SCC is therefore a direct measure of the herd's subclinical mastitis burden — the cases nobody has noticed.
Below 200,000 cells/ml is a healthy herd. Between 200,000 and 400,000 there is a meaningful subclinical problem. Above 400,000 there is milk loss happening every day, and in export-facing supply chains a penalty or a rejection.
The loss is real and it is quiet: an animal with a linear score of 4 gives roughly 5% less milk than she should, and one at 6 gives roughly 15% less. Nothing about her looks wrong.
Method
Tracing a high bulk tank count
It is rarely the whole herd
A bulk tank at 500,000 is almost never every animal at 500,000. It is usually a small number of chronically infected animals with counts in the millions, diluted by everyone else. Find them and the tank number moves immediately.
Test per animal, not just the tank
Individual SCC — from a DHI-style test or a portable cell counter — identifies the contributors directly. Without it you are treating a herd for the sins of four animals.
California Mastitis Test as the field version
A CMT paddle at the parlour costs almost nothing and flags high-cell quarters in about thirty seconds. Less precise than a lab count, and entirely good enough to build a shortlist.
Track the linear score, not the raw count
Raw SCC is skewed and awkward to average. The linear score converts it to a scale where the arithmetic behaves, so trends over months are actually readable.
Separate new infections from chronic ones
An animal newly above threshold this month is a management problem — hygiene, milking routine, environment. One above threshold every month for six months is a culling decision. They need different responses and averaging them together hides both.
What to do about it
By category
New infections
Look at milking routine and environment: pre- and post-dipping, clean dry bedding, teat condition, liner wear and vacuum level. Most new infections are contracted between milkings, not during them.
Existing infections mid-lactation
Treat clinical cases properly and record the withdrawal period. Cure rates for subclinical cases mid-lactation are poor, and repeat treatment of an animal that will not cure is money spent on milk you then have to discard.
Chronic animals
Dry cow therapy at dry-off is where most cures actually happen. An animal that has been high through two consecutive dry periods is unlikely to become profitable, and keeping her is a decision about sentiment rather than arithmetic.
Order of milking
Milk known high-SCC animals last, or with separate equipment. This one change costs nothing and stops the contagious organisms travelling down the line.
Why this needs records rather than judgement
Every step above depends on knowing which animal, in which month, at what count. A bulk tank number tells you there is a problem; only per-animal history tells you whose problem it is, whether she is new or chronic, and whether last month's treatment worked.
Farms that lower SCC and keep it low almost always have that history. Farms that treat reactively usually have the same four animals still in the herd a year later.
Questions
Common questions
What is a good somatic cell count?
Under 200,000 cells/ml in the bulk tank is a healthy herd. Above 400,000 there is measurable daily milk loss and, in many supply contracts, a price penalty.
How much milk does high SCC actually cost?
Roughly 5% at a linear score of 4 and around 15% at a score of 6, in an animal showing no clinical signs at all.
Can high SCC be cured mid-lactation?
Sometimes, but cure rates are much better at dry-off. Dry cow therapy is where most genuine cures happen; mid-lactation treatment of subclinical cases often just adds a withdrawal period.
Does high SCC affect fat and SNF?
It lowers SNF, particularly the casein fraction, and it shortens shelf life. In a fat-and-SNF pricing system that shows up directly in what the animal earns.
Numbers beat opinions
Lactra computes these figures from your own records daily. Free for 20 animals, no card for the trial.