Somatic Cell Count and Milk Quality: What the Numbers Mean and the 750,000 Line

Every load of milk that leaves a dairy farm is tested. Two numbers on the report matter most to a producer: the somatic cell count, a measure of udder health, and the bacteria count, a measure of how clean the milk was when it was produced and cooled. Those numbers affect the price a farm is paid, whether it can ship at all and how long the milk will last on a store shelf. For a buyer, they are the reason the milk in the carton is reliably safe and fresh.

This guide explains what the numbers mean and how farms bring them down. Limits and premium programs vary by state, buyer and market, so check your milk contract and your regulator. If you want to find dairy quality workshops near you, agriculture.directory can help you find agriculture events in your area.

What Somatic Cells Are

Somatic cells are mostly white blood cells that move into the udder to fight infection, along with a few cells shed from the udder lining. A healthy quarter has a low count. When bacteria invade, the count climbs as the cow's immune system responds. Because of that, the somatic cell count, or SCC, is used as an indicator of mastitis in the herd. A single cow's count tells you about her udder. The bulk tank count, which mixes milk from every cow in the herd, tells you about the herd as a whole. Our guide to mastitis in dairy cows explains the disease behind the numbers.

The Legal Limits

In the United States, the legal maximum bulk tank SCC for Grade A milk shipments is 750,000 cells per milliliter under the Pasteurized Milk Ordinance. A USDA Animal and Plant Health Inspection Service information sheet explains that a producer with two out of four shipments over the limit, usually tested 30 to 45 days apart, receives a written notice and must have an additional sample taken, and further action can follow. The European Union uses a stricter limit of 400,000 cells per milliliter, and U.S. producers whose rolling averages exceed that level may be unable to export milk to the EU. Support has grown for lowering the U.S. limit, but the standard has stayed at 750,000. Read the full monitoring report from USDA APHIS on bulk tank somatic cell counts.

Where Typical Farms Are

Most farms run far below the legal limit. The USDA information sheet reported a producer geometric mean bulk tank count of about 204,000 cells per milliliter in 2019 for the federal milk marketing orders it monitors, and noted that counts have declined since 2002. Many buyers pay premiums for low counts and penalize high ones, so the goal for most farms is well under the limit. Your milk buyer will tell you the targets and price adjustments that apply to you.

The Bacteria Count

The standard plate count measures bacteria in the milk. The Grade A limit for raw milk from a producer is 100,000 bacteria per milliliter under the ordinance. Ohio State University dairy specialists note that standard plate counts above about 50,000 colony-forming units per milliliter can point to problems such as poor cleaning of the milking system, inadequate udder preparation or poor cooling. Other tests, such as the laboratory pasteurized count and coliform count, help pinpoint whether bacteria are coming from the udder, dirty cows, dirty equipment or slow cooling. The Ohio State key mastitis control points article explains how to read these tests.

Why Counts Rise

• Contagious mastitis. Bacteria such as Staphylococcus aureus spread from cow to cow at milking, usually through hands, towels and milking units.
• Environmental mastitis. Bacteria from bedding and manure enter the udder between milkings, which links back to bedding and cleanliness, as the guide to cow comfort explains.
• Poor milking routine. Skipped teat disinfection, wet teats, or units attached at the wrong time, covered in the milking routine guide.
• Equipment problems. Worn liners, wrong vacuum levels or poor cleaning.
• Stress and nutrition. Crowding, heat, and the weeks around calving make cows more vulnerable, as the transition cow guide discusses.
• Late lactation and age. Counts naturally rise in older cows and near the end of lactation.

A Practical Plan to Bring Counts Down

1. Set a goal. Agree on a target with your veterinarian and milk buyer.
2. Find the source. Look at individual cow counts from DHI testing, which the guide to DHI records explains, and identify the cows with high counts. In many herds a small share of the cows causes most of the problem.
3. Culture the milk. Culturing samples from high-count cows tells you which bacteria are involved, which guides treatment and prevention.
4. Fix the routine. Consistent preparation, teat disinfection and attachment timing matter for every cow.
5. Check the equipment. Have the milking system tested on schedule by a qualified technician.
6. Treat, segregate or cull. Work with your veterinarian on which cows to treat, which to milk last and which to remove from the herd.
7. Keep the cows clean and comfortable. Dry bedding and uncrowded pens help.
8. Monitor monthly. Watch trends, not single results.

The National Mastitis Council publishes recommended milking procedures and a mastitis control program used by many dairy advisers.

Antibiotic Residues

High somatic cell counts and mastitis treatment are closely linked to the risk of antibiotic residues in milk. The USDA information sheet notes that multiple studies show operations with high counts are more likely to have milk that violates antibiotic residue standards. Follow every label withdrawal time, keep treatment records and test when required. Milk with residues cannot be sold.

The Consumer Side

If you buy milk, these numbers are why Grade A milk is a dependable product. Counts and bacteria levels are checked by the farm, the buyer and regulators, and pasteurization adds another layer of safety. Our guide to reading a milk label explains the terms you see in the store.

Common Mistakes

• Looking only at the bulk tank. Individual cow data finds the problem cows.
• Treating without culturing. You may use the wrong drug.
• Skipping equipment checks. Hidden faults raise counts.
• Letting inconsistent routines creep in. Written procedures help.
• Ignoring withdrawal times. Residues cost far more than the milk.

Farm.fm's page on dairy covers dairy news and background, and for a laugh, see farm.fm's piece on dairy farm regulations that multiply faster than the herd.