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AIPL RESEARCH REPORT
SCC2 (2-01)

Somatic cell counts of milk from Dairy Herd Improvement herds during 1999 and 2000

R.H. Miller and H.D. Norman
Animal Improvement Programs Laboratory, ARS-USDA, Beltsville, MD 20705-2350
301-504-8334 (voice) ~ 301-504-8092 (fax) ~ rlaipl@aipl.arsusda.gov ~ http://aipl.arsusda.gov

Test-day data from all herds enrolled in Dairy Herd Improvement (DHI) somatic cell testing during 1999 and 2000 (91% of all DHI herds) were examined to assess the status of national milk quality. All test-day data within a herd were included regardless of breed; data from owner-sampler herds were included as well. Cows with records that failed Animal Improvement Programs Laboratory (AIPL) editing procedures (for example, no sire identification) were excluded. However, the somatic cell counts (SCC's) of milk from such cows did not differ from those from the other cows in the herd. Somatic cell score (SCS) is reported to AIPL and was converted back to SCC in cells/milliliter [SCC = 2(SCS–3) × 100,000] for calculating herd and State averages.

Table 1 shows for each State in 1999 the total number of herd test days, the average number of cows (with usable records) per herd on test day, the average milk yield and SCC on test day, and the percentages of herd test days that exceeded four levels of SCC: 750,000, 600,000, 500,000, and 400,000 cells/ml. The current legal limit for bulk tank SCC is 750,000 cells/ml for Grade A producers; the lower limits shown have been proposed as future maximums. State and national average daily milk yields were weighted by the number of cows per herd test day. Herd, State, and national average SCC's were based on SCC's from individual cows that were weighted by milk yield on test day. Information from Alaska and Hawaii was not included because of sparse data. Table 2 shows corresponding data for 2000.

Nationally, average SCC during 2000 was 316,000 cells/ml, which was higher than the national average of 311,000 cells/ml for 1999 . Corresponding averages for 1995-1998 were 304,000, 308,000, 314,000 and 318,000. The percentages of herd test days that exceeded 750,000, 600,000, 500,000, and 400,000 cells/ml during year 2000 were 4.1, 9.4, 16.8 and 29.5, respectively. Thus, 4.1% of test-days from DHI herds that participated in somatic cell testing exceeded the present legal limit for SCC of bulk tank milk. This percentage may overestimate the percentage of herds that would have exceeded the legal limit for SCC of bulk tank milk on test day because the milk of cows treated for mastitis is excluded from the bulk tank but not excluded from the DHI test data. Also, the percentage of herd test days that exceeded the legal limit would have been higher than the percentage of herds that were rejected from the market because market exclusion only occurs after repeat violations.

Variation among States was large. Average SCC's were lower in the far West and higher in the Southeast. Although climatic conditions (temperature and humidity) probably contributed to regional SCC differences, SCC differences between geographically adjacent states were substantial, which suggests that mastitis-control regimes have an impact under similar climatic conditions.

These results show no improvement in national SCC. Greater efforts to improve milk quality are needed. State and national SCC's will continue to be summarized annually so that changes in SCC and trends in milk quality can be monitored.
 

Table 1. Characteristics of DHI herd test days for milk yield and SCC of milk during year 1999 by State. 
State Herd
test
days
Cows1 per 
herd
Average daily 
milk 
yield
Average 
SCC
Herd test days with SCC greater than: 
750,000 cells/ml 600,000 cells/ml 500,000 cells/ml 400,000 cells/ml

(no.) (no.) (lb) (cells/ml, 1000's) (%) (%) (%) (%)
Alabama 486 109.6 52.5 427 8.2 21.2 35.6 57.6
Arizona 334 598.5 70.3 296 0.6 1.5 5.4 14.4
Arkansas 501 51.4 52.7 448 14.4 26.0 32.5 48.9
California 10,058 352.4 74.9 248 1.2 2.9 5.6 12.8
Colorado 525 193.9 78.6 277 2.1 4.8 7.6 16.6
Connecticut 1,108 72.8 68.8 343 3.3 8.3 14.1 25.7
Delaware 292 93.2 66.5 316 0.0 1.0 5.8 15.1
Florida 162 233.9 65.5 533 13.0 34.0 50.6 69.8
Georgia 1,210 85.5 61.1 411 8.2 18.5 32.0 51.6
Idaho 1,883 146.0 75.3 300 3.2 7.5 13.3 24.5
Illinois 6,142 52.0 62.9 338 4.0 9.7 17.2 31.7
Indiana 4,094 45.9 61.5 377 6.9 13.8 22.9 36.5
Iowa 12,018 43.8 63.8 338 5.0 10.9 18.5 31.9
Kansas 2,968 53.4 61.8 415 10.0 18.9 29.8 44.4
Kentucky 2,244 50.9 57.0 376 6.8 13.7 24.0 39.3
Louisiana 722 64.8 52.3 454 9.4 20.5 35.0 58.7
Maine 1,442 56.1 65.2 310 3.8 9.2 17.3 27.6
Maryland 4,241 57.8 67.4 300 1.9 5.5 11.2 22.3
Massachusetts 1,118 60.6 65.3 342 4.5 11.9 19.4 31.6
Michigan 9,385 67.2 67.6 311 3.4 8.2 14.7 27.0
Minnesota 36,416 41.5 69.4 360 7.1 14.8 23.8 38.0
Mississippi 579 91.1 56.7 456 7.9 21.2 36.4 57.9
Missouri 4,182 47.1 57.5 383 6.7 15.1 24.8 40.4
Montana 512 60.0 70.1 287 0.6 2.0 5.3 13.9
Nebraska 2,310 61.0 64.2 368 6.2 13.2 21.9 35.8
Nevada 165 188.6 68.2 353 1.8 6.1 15.2 30.9
New Hampshire 1,087 72.3 71.1 333 3.2 8.2 15.5 27.0
New Jersey 809 63.7 66.5 372 4.7 12.9 21.9 39.6
New Mexico 220 460.8 75.8 269 1.8 5.9 13.2 23.6
New York 25,017 63.8 66.8 313 4.2 9.3 16.5 28.8
North Carolina 2,068 82.6 63.2 366 6.3 14.3 25.0 39.8
North Dakota 735 50.5 61.5 331 4.8 9.8 17.3 28.6
Ohio 10,283 51.0 65.9 328 4.5 9.9 17.0 29.9
Oklahoma 897 61.3 59.3 387 5.9 13.2 22.6 36.6
Oregon 2,326 101.5 72.3 278 1.2 3.5 6.8 15.7
Pennsylvania 44,763 44.7 65.4 331 2.9 7.8 15.3 29.0
Puerto Rico 591 75.7 41.0 423 9.0 20.8 36.4 55.2
Rhode Island 64 40.8 67.6 297 0.0 0.0 4.7 17.2
South Carolina 718 118.4 57.0 389 3.9 10.9 23.4 41.8
South Dakota 1,973 49.6 63.5 402 9.2 18.0 26.8 39.3
Tennessee 2,164 69.2 58.1 446 12.2 22.6 35.6 51.6
Texas 1,867 188.1 66.8 288 1.1 3.6 8.4 20.5
Utah 2,027 78.4 73.2 298 4.4 8.2 13.4 24.2
Vermont 4,419 54.8 64.0 318 2.9 7.6 14.0 25.8
Virginia 5,499 78.8 64.7 329 2.8 7.5 14.3 27.8
Washington 2,282 145.0 78.6 269 1.2 3.2 5.9 11.9
West Virginia 703 70.5 61.3 351 3.7 9.5 16.4 30.0
Wisconsin 57,732 47.3 67.6 306 3.4 7.9 14.3 25.8
Wyoming 23 124.6 74.0 242 0.0 0.0 0.0 0.0
United States 273,364 67.0 68.2 311 4.3 9.7 17.1 29.8

1Cows with usable records (less than total cows on test)


Table 2. Characteristics of DHI herd test days for milk yield and SCC of milk during year 2000 by State. 
State Herd
test
days
Cows1 per 
herd
Average daily 
milk 
yield
Average 
SCC
Herd test days with SCC greater than: 
750,000 cells/ml 600,000 cells/ml 500,000 cells/ml 400,000 cells/ml

(no.) (no.) (lb) (cells/ml, 1000's) (%) (%) (%) (%)
Alabama 412 117.1 53.8 441 8.5 18.0 32.0 54.4
Arizona 344 625.6 70.5 313 0.6 1.5 5.5 21.8
Arkansas 453 53.1 53.9 427 13.2 20.5 30.2 44.8
California 10,308 404.1 74.7 282 1.6 4.5 8.7 18.4
Colorado 519 202.1 80.7 280 0.0 2.1 3.8 12.5
Connecticut 1,044 69.4 69.1 326 2.7 7.7 14.2 24.7
Delaware 288 98.3 67.2 353 0.7 4.5 13.2 27.1
Florida 174 332.6 69.5 504 12.6 30.5 50.6 73.6
Georgia 1,169 86.2 62.7 409 8.5 18.0 31.8 51.1
Idaho 1,800 173.1 76.1 330 4.0 8.9 15.6 28.7
Illinois 5,753 54.6 64.9 327 3.6 8.9 16.3 29.3
Indiana 4,271 48.5 63.4 344 4.8 10.4 18.4 31.1
Iowa 11,264 46.7 65.7 334 4.4 10.3 18.4 31.5
Kansas 2,784 55.2 64.0 428 12.2 23.1 33.1 47.8
Kentucky 2,126 52.2 59.1 370 5.5 12.2 21.2 37.2
Louisiana 701 64.9 54.2 476 10.1 24.7 44.2 66.3
Maine 1,345 55.1 64.3 305 3.2 7.4 14.3 25.7
Maryland 3,898 61.9 67.2 330 3.1 7.8 15.9 30.3
Massachusetts 995 60.7 65.2 329 4.7 10.5 16.4 29.2
Michigan 8,870 69.6 69.0 293 2.8 7.2 13.4 24.1
Minnesota 34,510 49.7 68.0 362 6.3 13.9 23.5 38.3
Mississippi 520 89.9 59.5 448 4.0 18.1 35.2 56.1
Missouri 3,851 48.0 59.4 356 5.2 10.8 19.7 33.7
Montana 501 71.3 74.8 257 1.0 3.0 5.4 11.8
Nebraska 2,219 63.8 66.2 376 6.9 14.4 23.1 36.0
Nevada 164 187.5 71.8 332 4.3 7.9 15.8 26.8
New Hampshire 1,052 72.3 72.0 316 3.6 9.0 15.1 24.7
New Jersey 742 63.9 66.4 350 4.6 12.5 20.8 35.3
New Mexico 241 526.4 75.1 255 0.0 5.0 11.6 19.1
New York 23,308 63.9 67.0 303 4.1 9.0 15.7 27.3
North Carolina 2,116 84.6 64.5 370 6.0 13.4 24.0 41.4
North Dakota 675 54.4 62.9 342 5.5 11.0 16.6 28.6
Ohio 9,661 52.0 66.3 349 5.3 12.1 20.6 34.6
Oklahoma 789 63.9 61.7 396 8.9 16.5 25.2 37.4
Oregon 2,322 109.3 73.0 283 0.8 3.0 6.5 16.4
Pennsylvania 43,246 45.8 65.5 329 3.0 7.8 15.2 28.7
Puerto Rico 551 81.6 42.5 475 13.8 29.8 44.8 61.5
Rhode Island 62 39.8 64.7 218 0.0 0.0 3.2 8.1
South Carolina 729 120.4 60.0 379 3.2 11.7 22.0 42.9
South Dakota 1,815 51.4 65.0 409 9.3 17.1 26.1 40.1
Tennessee 2,103 66.0 59.0 420 9.8 19.1 31.1 45.9
Texas 1,838 208.7 68.4 294 1.1 3.2 8.5 20.0
Utah 1,907 86.8 75.0 285 2.3 5.3 10.6 20.8
Vermont 4,142 58.6 65.1 321 3.7 8.0 14.8 25.8
Virginia 5,251 79.8 66.4 338 2.5 7.0 13.9 29.3
Washington 2,306 150.4 79.4 289 1.9 3.6 7.2 16.1
West Virginia 641 67.2 63.5 379 5.3 11.7 21.2 37.0
Wisconsin 54,343 49.9 68.9 298 3.0 7.0 13.1 24.3
Wyoming 16 209.6 77.7 283 0.0 0.0 0.0 0.0
United States 260,139 73.3 69.1 316 4.1 9.4 16.8 29.5

1Cows with usable records (less than total cows on test)


Table 3. National averages of herd test days for milk yield and SCC of milk by year.
Year Herd
test
days
Cows1 per 
herd
Average daily 
milk 
yield
Average 
SCC
Herd test days with SCC greater than: 
750,000 cells/ml 600,000 cells/ml 500,000 cells/ml 400,000 cells/ml

(no.) (no.) (lb) (cells/ml, 1000's) (%) (%) (%) (%)
1995 265,844 50.0 65.3 304 4.1 9.3 16.0 27.2
1996 255,039 55.5 64.7 308 4.1 9.2 16.1 27.8
1997 287,789 57.4 66.4 314 4.2 9.5 16.6 28.8
1998 283,695 60.8 66.8 318 4.5 10.1 17.8 30.3
1999 273,364 67.0 68.2 311 4.3 9.7 17.1 29.8
2000 260,139 73.3 69.1 316 4.1 9.4 16.8 29.5

1Cows with usable records (less than total cows on test)