Three hundred twenty-one quarter, 207 whole udder, 310 bulk tank, and 93 tank-lorry milk samples were examined for confirmation of the presence of inhibitor by Delvotest SP assay. Four hundred twenty-six
Holstein cows of no drug treatment for at least 30 days from January 1998 to September 1999 were used. Reading time was 2.50, 2.75, and 3.00 h, and results of sampling were recorded by four types according
to comparison with the color of the well containing the control milk sample. False-positive outcome was identified by Delvotest SP assay in quarter (13 of 321), whole udder (9 of 207), and bulk tank milk
samples (4 of 310), but was not shown on tank-lorry milk samples (0 of 93) at the reading time of 2.50 h. All of the 26 false-positive samples were negative from the examination after heat treatment at
82°C for 5 min. But, two bulk tank milk samples that appeared to have positive results in LacTek and Charm II tests were positive from the test following heat treatment. Somatic cell counts (SCC) were
related to the probability of a false-positive result. The more SCC increased, the more the occurrence of a false-positive result increased. In our investigations, 4 of 310 bulk tank milk samples at the
reading time of 2.50 h produced false-positive results, and no false-positive results were apparent at a reading time of 2.75 h. Also, the occurrence of false-positive results in quarter and whole udder
milk samples decreased when agar was cultured for 2.75 to 3.00 h. There were no false-positive results from tank-lorry milk samples. These results indicate that the Delvotest SP assay may provide a suitable
means for the detection of drug residues in not only quarter and whole udder milk of cows but also in bulk tank and tank-lorry milk following reading times of 2.75 to 3.00 h.
Document Type: Research Article
Department of Veterinary Public Health, Faculty of Agriculture, Miyazaki University, Kibanadai-Nishi, Gakuen, Miyazaki-Shi 889-2192, Japan
Publication date: August 1, 2001
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