Somatic cell count is the single best number for udder health. It's mostly white blood cells — the more the udder is fighting infection, the higher the count. A rising bulk-tank SCC means subclinical mastitis is spreading before you ever see a clot, and most milk buyers dock your price (or reject milk) above a threshold.
Know your targets - Under 100,000 cells/mL — excellent, essentially infection-free. - 100,000–200,000 — good; the usual goal for a well-run herd. - 200,000–400,000 — subclinical infection is present and costing you yield. - Over 400,000 — most regulators/buyers penalise here; act now. - Every doubling of SCC above 50,000 costs roughly 0.4–0.5 kg of milk per cow per day in lost production — that's the hidden tax.
Step 1: find the cows driving it Bulk-tank SCC is an average. The damage usually comes from a handful of chronic high-SCC cows. Use a California Mastitis Test (CMT) cow-side, or individual-cow SCC if your recording scheme offers it, to identify them. You can't manage what you haven't located.
Step 2: fix the milking routine (biggest, cheapest win) - Pre-dip, wipe, strip, attach, post-dip — every cow, every time. Foremilk stripping removes the highest-bacteria first squirts and spots clinical cases early. - Post-milking teat dip is non-negotiable — it's the cheapest mastitis control there is. - Wear gloves; bare hands spread contagious bacteria (Staph aureus, Strep ag) cow to cow. - Check liner condition and pulsation/vacuum. Worn liners and bad vacuum cause teat-end damage that lets bacteria in. - Milk known infected cows last so the cluster doesn't carry infection to clean cows.
Step 3: clean, dry environment between milkings Environmental bugs (E. coli, environmental Strep, Klebsiella) come from manure and wet bedding. Scrape alleys, keep cubicles/bedding clean and dry, avoid overcrowding. Sand bedding is the gold standard for this reason (see "Sand bedding ROI").
Step 4: dry-cow management The dry period is when many infections are cured — or acquired. Use dry-cow therapy and/or internal teat sealant as advised by your vet, and keep the dry-cow environment as clean as the milking herd's. (See "How to dry off a dairy cow.")
Step 5: cull the incurables Some chronic Staph aureus cows will never clear no matter what you spend. A cow that's been over 400,000 across several tests, hasn't responded to treatment, and is spreading to others is costing you more than she earns. Culling her drops your whole-herd average.
The discipline that holds it SCC creeps back the moment routine slips. Track bulk-tank SCC every collection, CMT-test the high cows monthly, and treat any sudden jump as a "which cow?" investigation, not a number to live with.
Sources AHDB Dairy — Mastitis Control Plan & SCC management. National Mastitis Council — Recommended Mastitis Control Program. University of Wisconsin Milk Quality — Somatic Cell Counts.