The 2016 summary of Dairy Herd Improvement (DHI) test-day results revealed somatic cell counts (SCC) were down compared to a year earlier.
Nationally, average 2016 test-day herd SCC was 203,000 cells per milliliter, down 1,000 cells per milliliter from 2015 and down 85,000 since 2006, according to the Council of Dairy Cattle Breeding and the USDA’s Animal Improvement Programs Laboratory.
Test-day data from all herds enrolled in Dairy Herd Improvement (DHI) somatic cell testing during 2016 (98.5 percent of all DHI herds and 96.9 percent 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
These tables include individual state data for herd test days, average number of cows per herd on test, 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 milliliter, the current federal limit for bulk tank SCC for Grade A producers; and the percent of test days over 400,000 cells per milliliter, the current maximum level for milk headed to the European Union 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.
Variation among states remains large. State average SCC generally was lower than the national average in the Northeast, Mountain and Western states but higher for a few states in the Southeast.
Although climatic conditions (temperature and humidity) surely contributed to regional SCC levels, differences between adjacent states were substantial, suggesting herd size and mastitis-control practices are impacting state differences as well.
The increase in cows per herd continued, from 185.9 in 2015 to 196.0 in 2016. Test-day milk yield was up from 77.2 to 78.1 pounds. As herd size increased, milk yield generally increased and SCC declined.
The National Conference on Interstate Milk Shipments was considering a proposal to lower the maximum allowable SCC in milk to 400,000 cells per milliliter during its meeting, May 12-17 in Grand Rapids, Michigan. (The vote on that proposal was not available at Progressive Dairyman’s deadline.)
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If approved, and based on 2016 DHI SCC data, 16.7 percent of monthly tests for herds of fewer than 50 cows would fall above that limit, compared to 10.3 percent for herds with 50 to 99 cows, 7.3 percent for herds with 100 to 149 cows and only 1.0 percent for herds with over 3,000 cows.
Seasonality also has an impact. SCC increased from April through August and then declined from August through November. The highest-quality milk was produced in November and December. 
Visit Council on Dairy Cattle Breeding to see the full report.
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Dave Natzke
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