Table 1. Distribution of drug residues in nonsaleable raw milk samples from dairy farms detected by 3 commercial enzyme-linked receptor-binding assay (SNAP) tests and liquid chromatography-tandem mass spectrometry (LC-MS/MS).
| Description | Distribution (%) |
|---|---|
| Result of commercial SNAP screening test1 (n = 34) | |
| Positive | 82.3 |
| Negative | 17.7 |
| Distribution by drug class (by SNAP tests2; n = 28) | |
| Only β-lactams | 75.0 |
| β-Lactams and tetracycline | 14.3 |
| β-Lactams and sulfamethazine | 7.1 |
| β-Lactams, sulfamethazine, and tetracycline | 3.6 |
| Distribution by drug class (by LC-MS/MS3; n = 28) | |
| Negative | 50 |
| Only β-lactams | 43 |
| β-Lactams and sulfonamide | 3.5 |
| β-Lactams and tetracycline | 3.5 |
1
Positive = milk samples testing positive for at least 1 of the 2 commercial SNAP tests used; negative = milk samples testing negative for all 3 SNAP tests used.
2
Milk samples testing positive for the New SNAP Beta-lactam Test Kit, SNAP Tetracycline Test Kit, SNAP Sulfamethazine Test Kit (Idexx Laboratories Inc., Westbrook, ME).
3
Negative = milk samples with no drug residues observed by LC-MS/MS; other categories show distribution of samples with drug residues belonging to the described drug classes at concentrations above the limit of quantification for LC-MS/MS.