Objective—To determine whether somatic cell
counts (SCCs) or California mastitis test (CMT) scores
for individual quarter milk samples could be used to
detect subclinical intramammary infection among
dairy cattle in a herd with a high bulk tank SCC.
Design—Prospective clinical trial.
Animals—278 Holstein-Friesian dairy cattle from a
Procedure—Individual quarter milk samples were collected
and submitted for bacterial culture, California
mastitis testing, and determination of SCC. Additional
milk samples were collected 34 days later and submitted
for bacterial culture.
Results—During the initial visit to the herd, milk samples
were collected from all 278 cows. However,
because of blind mammary quarters or missing data,
results for 1,057 quarter milk samples were included.
Bacterial culture did not yield any growth for 622
(58.8%) of these samples. Regardless of the cutoff
that was used, sensitivity of the CMT score was ≤ 0.50
and sensitivity of the SCC linear score (SCS) was
≤ 0.60. For 497 mammary quarters, results of bacterial
culture of samples collected 34 days apart were concordant;
bacterial culture did not yield any growth for
342 (68.8%) of these quarters. Regardless of the cutoff
that was used, sensitivity of the CMT score was
≤ 0.61 and sensitivity of the SCS was ≤ 0.76 for mammary
quarters with concordant bacterial culture results.
Conclusions and Clinical Relevance—Results suggest
that neither CMT score nor SCC is sensitive
enough to be useful as a screening test for identifying
infected mammary quarters among dairy cattle in a
herd with high bulk tank SCC. ( J Am Vet Med Assoc 2004;224:419–423)