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SCC23 (2-22)

Milk somatic cell count from Dairy Herd Improvement herds during

H.D. Norman, F.L. Guinan, J.H. Megonigal, Jr., and João Dürr
Council on Dairy Cattle Breeding, Bowie, MD 20716
301-525-2006 ~ duane.norman@uscdcb.com ~ https://www.uscdcb.com

Test-day data from all herds enrolled in Dairy Herd Improvement (DHI) somatic cell testing during (98.4% of all DHI herds and 96.0% 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. Somatic cell score (SCS) of milk is reported to the Council on Dairy Cattle Breeding (CDCB) as part of an individual cow's test-day yield information. The test-day data used by the CDCB were provided by the Dairy Records Processing Centers (DRPC). The SCS was converted back to a milk somatic cell count (SCC) in cells per milliliter [SCC = 2(SCS − 3) × 100,000] for calculating herd and state averages.

Table 1 shows total number of herd test days, average number of cows with usable records per herd on test day, average test-day milk yield, fat and protein percentages, and herd SCC. It also shows the percentages of herd test days that exceeded four levels of SCC (750,000, 600,000, 500,000, and 400,000 cells/mL) for each state during . The current legal limit for bulk tank SCC is 750,000 cells/mL for Grade A producers; lowering the limit has been proposed periodically by a number of dairy organizations. A few states have lowered their SCC limits beyond the federal requirements. State and national average daily milk, fat and protein yields were weighted by number of cows per herd test day. Fat and protein percentages were determined by dividing their yield averages by millk yield. Herd, state, and national average SCCs were based on SCCs from individual cows that were weighted by milk yield on test day. This weighting assures that SCC and milk component percentages represent all milk produced in the catagories shown. Percentages of herd test days by SCC level are for herd test days that included records from at least 10 cows. Nationally, average DHI SCC during was 179,000 cells/mL, which was just 1,000 cells/mL higher than last year's average.

Variation among states (Table 1) remains large. State average SCC generally was lower than the national average for most northern states and nearly always higher for the southeastern states (Figure 1). Although climatic conditions (temperature and humidity) surely contributed to regional SCC levels, differences between adjacent states were large, suggesting herd size and mastitis-control practices are impacting state differences as well.

Corresponding national averages for 1995 through are in Table 2. National average test-day herd SCC had declined every year except three prior to 2001, which had the highest SCC at 322,000 cells/mL. The percentage of herd test days that exceeded 750,000, 600,000, 500,000, and 400,000 cells/mL during was 1.2, 2.5, 4.4, and 8.5, respectively, showing favorable declines in the last two years. The DHI herd test days that were higher than the present legal limit for bulk tank SCC (1.2%) overestimate the actual percentage of herds that shipped milk exceeding the legal limit because milk of cows treated for mastitis is excluded from the bulk tank even though included in DHI test data. The percentage of herd test-days that exceeded the legal limit also would have been higher than the percentage of herds that were rejected from the market because market exclusion only occurs after repeated violations.

Herd size has been increasing (Table 2). The increase in cows per herd was large, from 252.4 in 2020 to 260.1 in . Test-day milk yield increased from 79.5 to 80.6 pounds. The large decline in SCC since 2001 has been beneficial and hopefully a reduction will continue as a result of improved management practices including directed culling and genetic selection. Genetic selection is contributing more to improvement in milk quality than in the past. The general trend for lower percentage of herd test-days above the thresholds is continuing. State and national SCCs for DHI herds will continue to be summarized annually so that changes in SCCs and it's implications for milk quality can be monitored.

Table 3 reports average test-day milk yield and herd SCC during by herd size. As herd size increased up to 1,000 cows, milk yield increased amd SCC declined. A remaining concern is the percentage of test days for herds with less than 50 cows over the current and possible future limits. If the limit was set at 400,000 cell/mL, 14.5% of monthly tests would fall above the limit for herds with fewer than 50 cows, 7.4% for herds with 50 to 99 cows, 5.2% for herds with 100 to 149 cows, but only 0.2% for herds with over 4,000 cows. Because small herds contribute less each year to the total milk supply (see herd-average reports), the general trend is for improved milk quality as large herds generally have lower SCCs.

Table 4 reports average test-day milk yield, fat and protein percentages, and herd SCC during by month, and the seasonal pattern for milk quality is shown in Figure 2. Milk yield per cow was highest in April through June and was lowest in November. The highest and lowest months differed by 3.1 pounds; SCC increased from April to August and then declined through January. The seasonal pattern for fat and protein percentages are shown in Figure 3. The milk with the highest fat and protein percentages was produced in November and December. The months with the lowest fat and protein percentages were June through August.


SCC, fat and protein characteristics by state  
Table 1. Characteristics of test-day milk yield, somatic cell count (SCC), fat and protein percentages from Dairy Herd Improvement herds by state during

  Herd test days1 Cows2 per herd Average daily milk yield Average Fat Average Protein Average SCC Herd test days3 with SCC greater than
State (no.) (no.) (lb) (%) (%) (cells/ml, 1000's) 750,000 cells/ml
(%)
600,000 cells/ml
(%)
500,000 cells/ml
(%)
400,000 cells/ml
(%)
Alabama 19 25.8 64.0 3.49 3.01 303 5.3 5.3 5.3 5.3
Arizona 118 2603.2 77.3 3.70 3.14 170 0.0 0.0 0.0 0.0
Arkansas 82 112.4 49.4 3.96 3.25 351 1.2 4.9 12.2 29.3
California 5,005 1287.9 78.7 3.99 3.11 191 0.5 1.2 2.1 4.3
Colorado 223 1064.9 82.1 3.84 3.12 180 0.4 0.4 0.9 5.8
Connecticut 389 161.2 76.5 4.03 3.06 199 1.3 2.3 4.4 9.5
Delaware 93 138.6 73.9 4.13 3.20 242 0.0 0.0 0.0 4.3
Florida 123 1332.2 81.0 3.63 3.06 223 0.8 1.6 5.7 10.6
Georgia 296 195.7 79.0 3.93 3.12 212 0.7 1.0 3.4 12.5
Idaho 867 1204.7 80.7 3.95 3.24 148 0.5 0.5 0.9 1.6
Illinois 1,782 153.9 82.2 4.00 3.16 204 1.5 2.9 4.4 9.1
Indiana 1,481 206.8 82.0 3.99 3.16 191 0.8 2.2 3.8 8.0
Iowa 3,151 247.8 80.6 4.13 3.24 186 0.9 1.9 3.8 8.8
Kansas 819 232.1 85.1 3.83 3.23 208 0.6 2.7 6.8 17.6
Kentucky 615 132.9 83.5 3.59 3.09 257 1.8 3.3 5.5 11.4
Louisiana 124 70.8 60.1 3.82 3.13 301 7.3 7.3 16.9 25.8
Maine 759 124.3 78.1 4.09 3.13 179 0.8 2.0 4.2 7.6
Maryland 1,589 106.4 73.5 3.99 3.12 205 1.1 2.7 5.6 11.3
Massachusetts 467 50.2 66.7 4.17 3.21 199 1.9 3.0 5.6 9.9
Mexico 1 299.0 75.8 3.79 3.31 258 0.0 0.0 0.0 0.0
Michigan 3,438 374.2 85.7 3.91 3.15 150 0.3 0.6 1.3 3.4
Minnesota 9,585 158.0 80.0 4.08 3.22 202 1.9 4.0 7.0 12.9
Mississippi 131 121.8 54.7 4.12 3.43 276 3.1 9.2 16.0 21.4
Missouri 1,267 70.2 64.6 3.94 3.23 258 4.8 7.7 12.1 19.6
Montana 88 145.1 77.7 3.93 3.11 183 0.0 0.0 1.1 1.1
Nebraska 438 403.2 73.7 4.05 3.23 193 3.0 5.0 8.4 15.1
Nevada 7 2132.6 79.7 3.94 3.22 191 0.0 0.0 0.0 0.0
New Hampshire 462 97.3 73.4 4.33 3.21 154 1.7 2.6 4.8 8.0
New Jersey 268 65.7 71.1 3.88 3.11 262 4.1 7.1 12.3 22.0
New Mexico 109 3259.3 76.8 3.82 3.27 175 0.0 0.0 0.0 0.0
New York 9,893 255.2 83.8 4.01 3.15 174 0.6 1.6 3.2 7.2
North Carolina 609 238.6 81.1 4.09 3.15 192 1.3 2.6 4.9 12.5
North Dakota 106 339.1 83.4 3.89 3.25 170 0.9 1.9 5.7 10.4
Ohio 4,022 131.2 80.2 4.06 3.19 180 1.0 2.1 3.6 7.3
Oklahoma 229 78.0 57.6 3.84 3.27 307 4.4 8.7 14.4 24.0
Oregon 737 330.8 64.5 4.59 3.54 153 0.4 1.6 2.2 4.9
Pennsylvania 23,862 80.3 78.7 3.99 3.14 189 1.1 2.2 4.0 7.8
Rhode Island 21 40.0 77.6 4.17 3.20 190 0.0 0.0 0.0 0.0
South Carolina 163 157.7 61.8 4.14 3.30 251 2.5 3.7 3.7 11.7
South Dakota 391 776.5 76.8 4.22 3.35 202 0.5 1.5 3.6 8.4
Tennessee 358 100.0 65.8 4.11 3.13 274 1.7 3.6 8.4 16.2
Texas 556 1885.5 69.6 4.29 3.46 194 0.2 2.7 7.0 14.6
Utah 474 258.3 74.7 4.14 3.30 157 0.6 1.3 1.3 3.0
Vermont 1,963 170.7 79.0 4.07 3.22 149 0.6 1.6 2.4 4.6
Virginia 1,519 148.6 78.6 3.89 3.09 204 0.9 2.1 3.8 7.4
Washington 452 887.8 79.2 4.07 3.25 158 1.1 2.4 3.5 5.8
West Virginia 85 64.6 66.6 3.86 3.18 206 0.0 0.0 5.9 15.3
Wisconsin 22,114 210.3 87.0 4.03 3.16 159 1.7 3.0 4.8 8.4
United States4 101,350 260.1 80.6 4.01 3.17 179 1.2 2.5 4.4 8.5

1All herd test days with usable records.
2Cows with usable records (less than total cows on test).
3Herd test days with ≥10 usable records.
4US Average includes a few records from Mexican herds.


SCC, fat and protein characteristics by year  
Table 2. National averages for test-day milk yield, somatic cell count (SCC), fat and protein percentages from Dairy Herd Improvement herds by year

  Herd test days1 Cows2 per herd Average daily milk yield Average Fat Average Protein Average SCC Herd test days3 with SCC greater than
Year (no.) (no.) (lb) (%) (%) (cells/ml, 1000's) 750,000 cells/ml
(%)
600,000 cells/ml
(%)
500,000 cells/ml
(%)
400,000 cells/ml
(%)
1995 265,844 50.0 65.3 3.63 2.97 304 4.1 9.3 16.0 27.2
1996 255,039 55.5 64.7 3.69 2.98 308 4.1 9.2 16.1 27.8
1997 287,789 57.4 66.4 3.66 2.91 314 4.2 9.5 16.6 28.8
1998 283,695 60.8 66.8 3.67 2.96 318 4.5 10.1 17.8 30.3
1999 273,364 67.0 68.2 3.69 2.93 311 4.3 9.7 17.1 29.8
2000 260,139 73.3 69.1 3.70 2.95 316 4.1 9.4 16.8 29.5
2001 244,940 79.1 69.0 3.67 2.95 322 4.9 10.6 18.2 31.1
20024 267,809 77.5 69.5 3.69 2.95 320 5.6 11.0 18.1 30.0
2003 251,182 80.5 69.6 3.68 2.94 319 5.6 11.2 18.4 30.4
2004 240,938 85.7 69.4 3.68 2.95 295 4.7 9.4 15.5 26.4
2005 234,585 90.3 71.1 3.67 2.95 296 4.7 9.2 15.3 25.8
20065 236,191 115.5 71.2 3.69 2.96 288 3.9 8.3 14.3 25.2
2007 227,626 125.1 71.4 3.68 2.98 276 3.5 7.6 13.4 24.0
2008 222,245 131.7 71.7 3.64 2.96 262 3.4 7.1 12.5 22.4
2009 204,195 136.1 72.1 3.68 3.00 233 2.7 5.8 10.3 18.9
2010 198,218 145.2 72.7 3.65 3.01 228 2.7 5.7 10.0 18.0
2011 191,375 154.6 73.1 3.72 3.04 217 2.3 4.8 8.5 15.7
2012 184,927 161.8 74.2 3.73 3.06 200 1.5 3.3 6.1 12.0
2013 177,944 167.8 75.2 3.78 3.08 199 1.5 3.2 5.9 11.6
2014 173,260 177.3 76.2 3.77 3.09 200 1.6 3.4 6.0 11.6
2015 166,970 185.9 77.2 3.77 3.07 204 1.6 3.3 6.0 11.6
2016 157,218 196.0 78.1 3.80 3.08 203 1.6 3.2 5.7 11.1
2017 149,130 202.5 78.1 3.85 3.10 197 1.6 3.2 5.7 10.8
2018 133,513 222.7 77.9 3.90 3.12 191 1.7 3.4 5.9 11.0
2019 117,631 244.3 78.3 3.94 3.14 187 1.5 2.9 5.2 9.9
2020 108,633 252.5 79.5 3.97 3.14 178 1.2 2.5 4.3 8.3
2021 101,350 260.1 80.6 4.01 3.17 179 1.2 2.5 4.4 8.5
Annual trend -6,654 8.0*** 0.6***     -6.6*** -0.2*** -0.4*** -0.6*** -1.0***

1All herd test days with usable records.
2Cows with usable records (less than total cows on test).
3Herd test days with ≥10 usable records.
4Summary characteristics for 2002 were recalculated to include more complete data than were available at the time of initial reporting.
5Cows per herd included records with missing sire identification starting in 2006; those records were not included in prior years.
***Significant (P ≤ 0.001) linear regression.


SCC, fat and protein characteristics by herd size  
Table 3. Characteristics of test-day milk yield, somatic cell count (SCC), fat and protein percentages from Dairy Herd Improvement herds during by herd size

Herd size1 Herd test days2 Cows3 per herd Average daily milk yield Average Fat Average Protein Average SCC Herd test days4 with SCC greater than
(cows) (no.) (no.) (lb) (%) (%) (cells/ml, 1000's) 750,000 cells/ml
(%)
600,000 cells/ml
(%)
500,000 cells/ml
(%)
400,000 cells/ml
(%)
<50 37,937 25.9 67.3 4.02 3.16 219 3.0 5.5 8.7 14.5
50 - 99 26,158 70.1 72.6 4.01 3.17 199 0.3 1.2 3.0 7.4
100 - 149 9,702 120.8 75.3 4.02 3.18 189 0.2 0.5 1.7 5.2
150 - 199 5,206 172.6 77.5 4.00 3.16 187 0.1 0.5 1.4 4.2
200 - 299 5,785 242.6 79.7 4.00 3.17 177 0.0 0.3 1.0 3.0
300 - 499 5,323 386.5 83.0 4.00 3.16 170 0.0 0.3 0.9 2.6
500 - 999 5,079 691.8 85.1 4.01 3.17 169 0.0 0.1 0.3 1.7
1000 - 1999 3,596 1403.4 83.6 4.01 3.12 176 0.0 0.0 0.0 0.7
2000 - 2999 1,313 2458.1 83.7 4.02 3.11 176 0.0 0.0 0.0 0.2
3000 - 3999 603 3446.9 80.6 4.01 3.22 185 0.0 0.0 0.0 1.0
>4000 648 6404.0 79.0 4.04 3.29 177 0.0 0.0 0.2 0.2
All herds 101,350 260.1 80.6 4.01 3.17 179 1.2 2.5 4.4 8.5

1Number of cows reported in milk.
2All herd test days with usable records.
3Cows with usable records (less than total cows on test).
4Herd test days with ≥10 usable records.


SCC, fat and protein characteristics by month  
Table 4. Characteristics of test-day milk yield, somatic cell score (SCC), fat and protein percentages from Dairy Herd Improvement herds during by month

  Herd test days1 Cows2 per herd Average daily milk yield Average Fat Average Protein Average SCC Herd test days3 with SCC greater than
Month (no.) (no.) (lb) (%) (%) (cells/ml, 1000's) 750,000 cells/ml
(%)
600,000 cells/ml
(%)
500,000 cells/ml
(%)
400,000 cells/ml
(%)
January 9,174 253.1 80.7 4.12 3.22 167 1.0 1.8 3.4 6.6
February 8,318 259.7 81.0 4.11 3.22 172 1.0 2.1 3.4 6.9
March 9,053 266.4 81.1 4.07 3.20 171 1.0 2.2 4.0 7.5
April 8,870 255.4 81.9 4.00 3.16 167 0.9 1.9 3.4 6.8
May 8,716 262.9 82.0 3.96 3.15 169 1.1 1.8 3.3 6.6
June 8,395 258.4 81.6 3.89 3.09 182 1.2 2.3 4.2 8.3
July 8,500 260.2 80.9 3.88 3.07 197 1.6 3.4 5.9 11.2
August 7,829 255.0 79.8 3.89 3.08 203 1.7 3.6 6.5 12.2
September 8,201 263.0 79.7 3.93 3.13 196 2.0 3.9 6.7 12.4
October 8,380 254.0 79.7 4.03 3.21 183 1.4 3.2 5.5 10.0
November 7,553 275.0 78.9 4.14 3.27 172 1.1 2.0 3.4 7.1
December 8,361 259.8 80.2 4.14 3.26 172 1.0 2.0 3.5 6.9
Yearly 101,350 260.1 80.6 4.01 3.17 179 1.2 2.5 4.4 8.5

1All herd test days with usable records.
2Cows with usable records (less than total cows on test).
3Herd test days with ≥10 usable records.


Figure 1. Average test-day somatic cell count from Dairy Herd Improvement herds during by state



Figure 2. Average test-day milk yield and somatic cell count (SCC) from Dairy Herd Improvement herds during by month

SCC, fat and protein characteristics by month   The SGPlot Procedure

Figure 3. Average fat and protein percentages from Dairy Herd Improvement herds during by month

SCC, fat and protein characteristics by month   The SGPlot Procedure

We wish to acknowledge the contribution of the dairy producers who supplied data for this report through their participation in the DHI program and the DRPCs that processed and relayed the information on to CDCB.