Establishment of the Maximum Residual Limit in the Milk of Dairy Cows Injected Intramuscularly with Prednisolone

SIMPLE SUMMARY: Prednisolone (PSL) is generally used as an anti-inflammatory and analgesic agent. To establish a withdrawal period using PSL in this study, PSL residual levels and withdrawal time (WT) were assessed in milk after PSL was administered to healthy cows. As a result, the LC-MS/MS method’s recovery rate, relative standard deviation, and detection sensitivity met all required standards. At 24 h after treatment, the amount of PSL in milk containing 10 and 20 mg/mL of PSL was lower than the LOD and the LOQ. The time limit for withdrawal was set at 12 h. In summary, since the residual withdrawal period of PSL in milk is shorter than that of the test drug, it suggests that the administration of PSL preparations will produce less milk wastage than that of previous recommendations. ABSTRACT: We measured the levels of prednisolone (PSL) residues in milk of intramuscularly dosed dairy cows and established a withdrawal time (WT) of PSL in milk. Eight healthy Holstein cows were injected with 10 (PSL-1) or 20 (PSL-2) mL of 10 mg/mL of PSL, and then, their milk was sampled at 12 h intervals for five days. PSL residue concentrations in milk were determined using LC-MS/MS. The correlation coefficient of the calibration curve was 0.9976. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.2 µg/kg and 0.6 μg/kg, respectively. Recoveries ranged from 96.5% to 110.0%, and the coefficient of variation was <5.64%. At 24 h after administration, PSL levels in PSL-1 and PSL-2 were below the LOQ in all milk samples. Although this study had a smaller sample size than the European Medicines Agency’s recommendations (n = 20), it was based on the Animal and Plant Quarantine Agency guidelines of the Republic of Korea (n = 8) for the determination of withdrawal periods in milk. We established the withdrawal period for both PSL-1 and PSL-2 in milk at 12 h. In conclusion, we developed an analytical method that is sensitive and can reliably detect PSL in milk, and our estimated WT of PSL in bovine milk is shorter than the current 3-day withdrawal period of PSL in commercial PSL products.