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United States Department of Agriculture

Agricultural Research Service

Title: National Survey of Herd Average Somatic Cell Counts on Dhi Test Days

Authors
item Miller, R - RETORED (ARS)
item Norman, H
item Wiggans, George
item Wright, Janice

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: December 15, 1998
Publication Date: N/A

Interpretive Summary: To assess the status of milk quality, more information is needed on milk somatic cell count (SCC) on a nationwide basis; SCC is an indicator of mastitis infection. This study provides a nationwide assessment of SCC, with particular reference to the 750,000 cells/ml ceiling; assesses regional variation in SCC, and describes seasonal changes in SCC. Data were esomatic cell scores (SCS) from test day records from Dairy Herd Improvemen (DHI) herds that were enrolled in mastitis screening programs and that had been submitted to USDA for calculation of genetic evaluations. Test day SCS were converted to test day SCC. Percentage of herd test days with an SCC of >750,000 cells/ml was determined for each State as well as percentage of those herds with an SCC of >750,000 cells/ml on 2 successive test days. Meeting a 750,000 cells/ml requirement test day SCC generally was not a problem for most herds. The frequency of herd test days with an SCC of >750,000 cells/ml was <5% for most States. However, regional differences were large. Herd averages for test day SCC were lowest in the West and highest in the South. Seasonal differences in herd averages for test day SCC were as expected: higher SCC in summer and lower in winter. Year differences were present during the winter and spring. Percentage of herds that exceed maximum allowable bulk tank SCC of >750,000 cells/ml on 2 successive test days was high: generally 15 to 25% but sometimes >30%. Records from cows treated with antibiotics were included in the data, and SCC averages in this study probably were higher than corresponding bulk tank readings. Greater efforts to improve milk quality clearly are needed.

Technical Abstract: Data were somatic cell scores (SCS) from test day records from Dairy Herd Improvement (DHI) herds that were enrolled in mastitis screening programs and that had been submitted to USDA for calculation of genetic evaluations. Test day SCS from 3,349,186 lactations during 1996-97 were converted to test day SCC. Percentage of herd test days with an SCC of >750,000 cells/ml lwas determined for each State as well as percentage of those herds with an SCC of >750,000 cells/ml on 2 successive test days. Number of herd test days ranged from 86 (Wyoming) to 103,392 (Wisconsin). State herd averages for test day SCC ranged from 254,000 cells/ml (Washington and Rhode Island) to 485,000 cells/ml (Tennessee). State herd averages were lowest in the West and highest in the South. Percentage of herd test days with an SCC of >750,000 cells/ml ranged from 0% (New Mexico and Wyoming) to 14.2% (Tennessee). For states with large cow populations, 15 to 25% of herds with ha test day SCC of >750,000 cells/ml exceeded 750,000 cells/ml on 2 successive test days. Monthly herd averages for test day SCC peaked in July and August and were lowest in October through January. Herd averages for January through April were higher in 1997 than in 1996; however, herd averages for November and December were slightly lower in 1997 than in 1996. Records from cows treated with antibiotics were included in the data, and SCC averages in this study probably were higher than corresponding bulk tank readings. Greater efforts to improve milk quality clearly are needed.

Last Modified: 9/1/2014
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