Authors: Karin Knappstein, Gertraud Suhren, Hans-Georg Walte, B.A. Slaghuis, R. T. Ferwerda- van Zonneveld
In conventional milking extended excretion periods of residues in milk exceeding the indicated withholding period are seldomly observed after antibiotic treatment of cows. Limited information is available if milking frequencies in automatic milking (AM) systems deviating from the regular milking times twice per day influence the excretion time of residues in milk. Therefore the present study was performed as part of the workpackage 5 "Prevention of antibiotic residues" within the European research project "Implications of the Introduction of Automatic Milking on Dairy Farms". In a previous study the excretion of antibiotic residues in milk of healthy cows in dependence on milking frequency was reported (D11).
In this report results of the second part of the investigation
performed on cows with clinical mastitis are presented. For the treatment
trials an udder injector containing cefquinome was selected, because
relatively long excretion periods and large variation of excretion time were
observed after application of this drug to cows without clinical symptoms of
16 cows with 22 cases of acute clinical mastitis were included. In 17 cases cows were milked two times per day with intervals of 10 and 14 hours. In 5 cases cows were milked less frequently with intervals of 16 hours. One udder quarter per cow was treated at three successive milking times except for 2 cows in which 2 udder quarters were treated at the same time, a third cow received additional intramuscular treatment with the same antibiotic. In none of the cows the withholding period for milk of 120 hours was exceeded. In general, the excretion times were shorter than in a worst case experiment with repeated treatment of 4 udder quarters in healthy cows.
Different approaches for determination of withholding periods
were applied. In contrast to the findings in healthy cows the milking
frequency was of no significant influence on excretion time of cefquinome in
milk. Only milk yield had a significant influence on excretion of residues in
milk leading to shorter excretion times in cows with higher average daily milk
yield during the experimental period.
From calculations based on results from excretion studies in healthy cows it can be concluded that the highest risk for bulk milk contamination due to carry over of milk from treated cows is for penicillin. The demands on automatic cleaning systems after milking of treated cows are rather high. In an experiment with 3 cefquinome treated cows no carry over of this compound was found into the milk of the next cow milked at the same place after performing a short cleaning cycle.
From the results of these studies and from the available literature recommendations are given for management of antibiotic treatment of cows in AM systems regarding farmer, veterinarian and AM manufacturer.