Impact of Automatic Milking on Excretion of Antibiotic Residues

Prevention of antibiotic residues in milk is an important aspect in milk production to ensure health protection for the consumer and high quality of milk for dairy processing. Limited information is available on the potential impact of milking frequencies associated with Automatic Milking (AM) on excretion of veterinary drugs in milk. Under experimental conditions the excretion of antibiotics in milk was studied in healthy cows (somatic cell count in composite milk below 100 000/ml) after intramammary treatment with 4 different commercially available drugs at milking frequencies of 3, 2 and 1.5 times per day. The concentrations of antibiotic residues in cow composite milk sampled at every milking time were determined by HPLC methods and compared to the Maximum Residue Limits (MRL) for each compound. For drugs containing cefquinome or penicillin or a combination of penicillin, nafcillin and dihydrostreptomycin significantly (p<0.05) shorter excretion periods were observed in cows milked 3 times per day compared to cows milked 1.5 times per day. For one drug containing ampicillin and colistin differences were not significant. Higher concentrations of residues in milk were determined with shorter intervals between treatment and next milking. After intramammary treatment of clinical mastitis with cefquinome no significant difference of excretion times was detected between cows milked 2 times (n=15) or 1.5 times (n=4) per day. In these cows only milk yield had a significant influence on excretion time with shorter excretion times in high yielding cows (p<0.05). The indicated withholding periods for milk were sufficient for all drugs. Nevertheless it is recommended to milk treated cows at least twice per day, because prolonged excretion was determined in healthy cows milked less frequently.