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In Focus: Management, genetics boost milk quality

Progressive Dairy Editor Dave Natzke Published on 07 May 2021

Improved management practices and increased attention to genetic selection helped overcome the added milk production and marketing challenges related to the COVID-19 pandemic in 2020.

As a result, U.S. milk attained new levels of quality last year, based on an annual summary of Dairy Herd Improvement (DHI) test-day results.



Nationally, average 2020 test-day herd somatic cell count (SCC) was 178,000 cells per milliliter (mL), down 9,000 cells per mL from 2020 and a fifth consecutive year of improvement, according to the Council of Dairy Cattle Breeding and the USDA’s Animal Improvement Programs Laboratory. The year-to-year improvement was the largest since 2011-12, and the U.S. average is now down 144,000 cells per mL since peaking at the turn of the century.

Test-day data from all herds enrolled in DHI somatic cell testing during 2020 (98.4% of all DHI herds and 96% of DHI cows) were examined to document the status of national milk quality. All test-day data within herds on any DHI test plan (including owner-sampler recording) were included.

Individual state data


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These tables include individual state data for herd test days, average number of cows per herd, average daily milk yield and average SCC on test day. It also breaks out two categories of SCC levels: the percent of days over 750,000 cells per mL, the current federal limit for bulk tank SCC for Grade A producers; and the percent of test days over 400,000 cells per mL, the current maximum level for milk headed to European Union (EU) and some other export markets. (A few states have lower SCC limits compared to federal requirements.)


Herd test days higher than the federal limit may overestimate the percentage of herds shipping milk exceeding that limit because milk from cows treated for mastitis is excluded from the bulk tank, even though it is included in DHI test data.

State improvement

Variation in SCC among states remains large but is narrowing. Although climatic conditions (temperature and humidity) contributed to regional SCC levels, differences between adjacent states were substantial, suggesting herd size and mastitis control practices are impacting state differences as well.

Average annual SCC in 16 states was at or less than the national average, led by Michigan, Idaho and Washington, all under 150,000 cells per mL. Oklahoma, Louisiana, Alabama and Arkansas averaged more than 320,000 cells per mL.

Forty states improved annual average SCC in 2020, with 10 states improving by 10,000 cells per mL or more compared to 2019. Largest improvements were in Alabama (-88,000 cells per mL), Nevada (-64,000 cells per mL) and Louisiana (-43,000 cells per mL). Other states with improvements of 25,000 to 38,000 cells per mL were Arkansas, Indiana, Oklahoma, Washington and Montana.

Average annual SCC rose by 20,000 cells per mL or more in Georgia, Kentucky and Delaware.

Herd sizes compared

After a significant 22-cow jump in 2019, the increase in cows per DHI herd was more subdued in 2020, up about eight cows, from 244.3 in 2019 to 252.5 in 2020.


Herds of all sizes exhibited improved SCC levels in 2020. Herds of 4,000 cows or more had the lowest average SCC, at 166,000 cells per mL.

A remaining concern is the percentage of test days for small herds over the current and possible future limits. If the limit was set at 400,000 cells per mL, about 14% of monthly tests would fall above the limit for herds with fewer than 50 cows, 7.6% for herds with 50 to 99 cows and 5% for herds with 100 to 149 cows.

Monthly breakouts

Looking at the calendar, U.S. average SCC posted double-digit declines in seven months of 2020, led by a drop of 16,000 cells per mL in July. SCC increased from May to August and then declined through December. Compared to a year earlier, monthly average SCC increased in only one month, November.

Milk, fat and protein data

The annual reported added fat and protein percentages in 2019, and both increased slightly among DHI herds in 2020. Test-day average milk yield rose about a pound to 79.5 pounds. Milk yield per cow was highest in April and June and was lowest in October, but the highest and lowest months only differed by 1.7 pounds.

The milk with the lowest SCC and highest fat and protein percentages was produced in December. The month with the lowest fat and protein percentages was July. end mark

To see the full report, visit Council on Dairy Cattle Breeding.

Dave Natzke
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