OXYTETRACYCLINE RESIDUES IN MILK OF COWS
TREATED FOR RETAINED PLACENTAS
-- abstracted from P. Dinsmore, R. Stevens, M. Cattell,
M. Salman, and S. Sundlof
Journal of the Amer. Vet. Med. Assn.
Nov. 15, 1996, Vol. 209, No. 10, p. 1753.
Oxytetracycline is an antibiotic routinely used in an extra-label manner for intrauterine
therapy. Research supporting the efficacy of intrauterine antibiotics is minimal, yet the practice is
common. A study was performed to establish the duration of oxytetracycline residues in milk
from cows with retained fetal membranes given the antimicrobial via intrauterine infusion. The
study also investigated whether the number of infusions or the presence of fever affected the
duration of residues.
Fifty-four Holstein cows with retained fetal membranes on a single 1,400-cow commercial
dairy were used in this study. Cows were treated once a day with 5 g of oxytetracycline by
intrauterine infusion for at least 2 days, or until the membranes were expelled. Cows that became
clinically ill (fever and off-feed) were also given procaine penicillin G at 20,000 IU/kg (9,000
IU/lb) of body weight, IM daily for 2 to 4 days. Milk samples were collected at 24-hour intervals
during treatment, and at 12-hour intervals after the last treatment. All samples were frozen and
submitted every 2 weeks for high performance liquid chromatography (HPLC) analysis for
Oxytetracycline was detected in milk of all cows during treatment, at a maximum
concentration ranging from 47 to 1,800 �g/kg (ppb). Duration of oxytetracycline residues after
the last infusion ranged from zero to 144 hours (6 days). Neither the number of infusions
received nor development of rectal temperature greater than 39.7�C (103.5�F) affected the
maximum concentration or the duration of oxytetracycline residues in milk.
Milk obtained from cows that are treated for retained fetal membranes by intrauterine
infusion of oxytetracycline may contain the drug for variable lengths of time. Milk should be
discarded to avoid illegal residues. Contact your veterinarian for appropriate withholding times.