This study investigated changes of milk production in dairy cows intramuscularly injected with drugs containing dexamethasone (DXM). Three types of dexamethasone formulations (Bueunde® (DXM 0.5 mg/mL), Dexason INJ.® (DXM 1 mg/mL) and Dexolone-20 inj.® (DXM 1 mg/mL)) were intramuscularly injected into sixteen healthy dairy cows each. Bueunde® was intramuscularly injected into 8 dairy cows with 5 mg (BED-1) and 10 mg (BED-2) of DXM once a day for 3 consecutive days, respectively. Dexason INJ.® was intramuscularly administered once into dairy cows with 20 mg (DXS-1, n=8) and 40 mg (DXS-2, n=8) of DXM, respectively. Dexolone-20 inj.® was intramuscularly injected once into dairy cows with 20 mg (DXS-1, n=8) and 40 mg (DXS-2, n=8) of DXM, respectively. Milk production (MP) of BED-1 and BED-2 significantly decreased during the drug administration and up to 48-hour post-drug treatment. Compared with the MP before drug administration, the MP of DXS-1 and DXL-1 was meaningfully decreased by 36 and 24-hour post-drug administration, respectively, and that in both DXS-2 and DXL-2 significantly decreased until 48-hour post-drug treatment. In conclusion, it was confirmed that the MP temporarily decreased by 48 hours after administration of DXM to dairy cows.

This study investigated chlorpheniramine maleate (CPM) residues in milk of intramuscularly dosed dairy cows and established the withdrawal time (WT) of CPM in milk. Sixteen healthy Holstein cows were injected with 10 (CPM-1) and 20 mL (CPM-2) of the drug containing 4 mg/mL of CPM, respectively. After administration of CPM, milk samples were collected from all cows at 12 hour intervals for 5 days. CPM residue concentrations in milk were determined using LC-MS/MS. The correlation coefficient of the calibration curve was 0.9956, and the limits of detection and quantification (LOQ) were 0.6 and 1.0 μg/kg, respectively. Recoveries ranged between 98.5-115.0%, and coefficient of variations were less than 10.96%. After treatment, CPM in CPM-1 and CPM-2 was detected below the LOQ in all milk samples at 12 hours. According to the European Medicines Agency’s guideline on determination of withdrawal periods for milk, withdrawal periods of both CPM-1 and CPM-2 in milk were established to 12 hours. In conclusion, the developed analytical method is sensitive and reliable for detection of CPM in milk, and the estimated WT of CPM in bovine milk will contribute to ensuring the safety of milk.