Author
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MILLER, R - RETIRED, ARS |
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Norman, H |
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Submitted to: AIPL Research Reports
Publication Type: Government Publication Publication Acceptance Date: 1/5/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Somatic cell count (SCC) of milk is a barometer of milk quality, and an elevated SCC is an indicator of mastitis. For Grade A producers, a milk shipment with a bulk tank SCC of >750,000 cells/ml triggers a process by which a producer's milk may be excluded from market. Also, additional premiums are paid for milk with a low bulk tank SCC. Because data on bulk tank SCC's are not readily available, SCC's from Dairy Herd Improvement (DHI) herds may help fill this void. Test-day data from all herds enrolled in DHI somatic cell testing during 1998 were examined to assess the status of national milk quality. The somatic cell scores that are sent to USDA were converted to somatic cell counts (SCC's) for calculating herd and State averages. Nationally, average SCC during 1998 was 318,000 cells/ml, which was higher than the national averages of 307,100 cells/ml for 1996 and 313,500 cells/ml for 1997. 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. Percentages of herd test days that exceeded SCC of 750,000, 600,000, 500,000 and 400,000 cells/ml were 4.5, 10.1, 17.8 and 30.3, respectively; the lower limits have been proposed as future maximums. Thus, 4.5% of test-day milk samples from DHI herds that participated in somatic cell testing exceeded the present legal limit for SCC of bulk tank milk. Greater efforts to improve milk quality are needed. More emphasis on price incentives to reward the production of quality milk might be a solution. Technical Abstract: Test-day data from herds enrolled in Dairy Herd Improvement (DHI) somatic cell testing during 1998 were examined to assess status of national milk quality. Somatic cell scores sent to USDA were converted to somatic cell counts (SCC's) for calculating herd and State means. State and national mean daily milk yields were weighted by number of cows per herd test day. Herd, State, and national mean SCC's were based on SCC's from individual cows weighted by milk yield on test day. Nationally, mean SCC during 1998 was 318,000 cells/ml, which was higher than national means of 307,100 cells/ml for 1996 and 313,500 cells/ml for 1997. Variation among States was large. Mean SCC's were lower in the far West and higher in the Southeast. Although climatic conditions (temperature and humidity) probably contributed to regional differences, SCC differences between geographically adjacent states were substantial, which suggests that mastitis-control regimes have an impact under similar climatic conditions. Percentages of herd test days that exceeded SCC of 750,000, 600,000, 500,000 and 400,000 cells/ml were 4.5, 10.1, 17.8 and 30.3, respectively. Current legal limit for bulk tank SCC is 750,000 cells/ml for Grade A producers; the lower limits have been proposed as future maximums. Thus, 4.5% of test-day milk samples from DHI herds that participated in somatic cell testing exceeded the present legal limit for SCC of bulk tank milk. This percentage may be an overestimate of percentage of herds that would have exceeded the legal limit because milk of cows treated for mastitis just prior to test day is excluded from the bulk tank. Also, percentage of herd test days exceeding the legal limit would have been higher than percentage of herds rejected from market because market exclusion only occurs after repeat violations. |
