1. 2004 H.D. Norman, A.H. Sanders,* R.H. Miller, and R.L. Powell Animal Improvement Programs Laboratory Agricutural Research Service, USDA, Beltsville, MD asanders@aipl.arsusda.gov Impact of participation in somatic cell count testing on herd average somatic cell score

2. ADSA-ASAS JOINT MEETING 2004 (2)A.H. Sanders 2004 National Mastitis Screening  93% of cows on DHI test plans participate in mastitis screening.  3.8 million cows.  25,000 herds.  20% less herds than in 2000, although number of cows unchanged.  Herd average somatic cell count (SCC) has increased since 1995, but was slightly lower in the last 2 years.

3. ADSA-ASAS JOINT MEETING 2004 (3)A.H. Sanders 2004 Objectives  Evaluate the effectiveness of mastitis screening in reducing herd average somatic cell score (SCS).  Investigate seasonal and regional differences in herd average SCS.

4. ADSA-ASAS JOINT MEETING 2004 (4)A.H. Sanders 2004 Data  Base herds selected  Started SCC testing after July 1995  Milked 2x for the first 30 months of testing  Herd Test day records screened  Dropped after >6 mo of no test  Included  10 cows with SCC records and  50% of cows in milk  Herds screened  >1 month of testing  1st month on test met test day record screening

5. ADSA-ASAS JOINT MEETING 2004 (5)A.H. Sanders 2004 Data  51,589 test days in 2950 herds  Included on herd test day records  Test date  Time herd on testing (mo)  Region  Calculated from cow test day records  Mean milk/cow  Mean SCS/cow (weighted by milk)

6. ADSA-ASAS JOINT MEETING 2004 (6)A.H. Sanders 2004 Regions Northeast Southeast Southwest Northwest Midwest 1089 222 1492 68 79

7. ADSA-ASAS JOINT MEETING 2004 (7)A.H. Sanders 2004 Initiation of SCC Testing by Region 0 100 200 300 400 500 600 700 800 1995 July - 199619971998199920002001200220032004 -June Year of First SCC Test Herds Northeast Midwest Northwest Southeast Southwest

8. ADSA-ASAS JOINT MEETING 2004 (8)A.H. Sanders 2004 Methods Model: SCS Herd TD = Herd + Season + Test month + Time on test Where: Season = calendar month Test month = months since June 1995 Time on test = months since herd’s first SCC test

9. ADSA-ASAS JOINT MEETING 2004 (9)A.H. Sanders 2004 Herd Somatic Cell Score

10. ADSA-ASAS JOINT MEETING 2004 (10)A.H. Sanders 2004 Regional Herd SCS Northeast Midwest Southeast

11. ADSA-ASAS JOINT MEETING 2004 (11)A.H. Sanders 2004 Persistence in Testing Herds testing: <1 year(678) >1 year(2272)

12. ADSA-ASAS JOINT MEETING 2004 (12)A.H. Sanders 2004 Mastitis Based Culling Decisions 2100 Herds with cows coded “culled for mastitis”

13. ADSA-ASAS JOINT MEETING 2004 (13)A.H. Sanders 2004 Mastitis Based Culling Decisions Northeast (841) Midwest (1011) Northwest(39) Southeast (151) Southwest (58)

14. ADSA-ASAS JOINT MEETING 2004 (14)A.H. Sanders 2004 Seasonal Effects by Region -0.15 -0.10 -0.05 0 0.05 0.10 0.15 0.20 0.25 0.30 JanFebMarAprMayJunJulAugSepOctNovDec Month Herd SCS Effect Northeast Midwest Southeast Northwest Southwest

15. ADSA-ASAS JOINT MEETING 2004 (15)A.H. Sanders 2004 Summary  Participation in mastitis screening may be helpful in reducing bulk tank SCC.  SCS is seasonally affected.  Culling for mastitis increased slightly during the first months on SCC testing.

16. ADSA-ASAS JOINT MEETING 2004 (16)A.H. Sanders 2004 Related Areas of Interest  Effect of changes in milking frequency on herd SCS  Effect of herd size and changes in herd size on herd SCS  Impact of individual cows (culling) vs. herd-wide effects on herd SCS