Antibiotic residues in milk following bulbar subconjunctival injection of procaine penicillin G in dairy cows.
OBJECTIVE
To determine whether, and at what time, penicillin enters milk at a concentration that is detectable following bulbar subconjunctival injection in lactating dairy cows.


METHODS
Randomized clinical trial.


METHODS
66 Holstein cows that were at least 2 weeks past calving and had not been treated with antibiotics in the preceding 30 days.


METHODS
Cows were randomly assigned to receive a treatment of 1 ml (300,000 units) procaine penicillin G by bulbar subconjunctival injection or remain untreated. Composite milk samples were collected immediately before treatment and 4, 10, 16, 22, 28, and 40 hours after treatment. Milk samples were tested by use of a commercial test for beta-lactam antibiotics.


RESULTS
Among penicillin-treated cows, the first positive test results were observed 4 hours after treatment, and the last positive result was observed 22 hours after treatment. The percentages of positive test results before treatment and at 4, 10, 16, 22, 28, and 40 hours after treatment were 0, 9, 87, 42, 8, 0, and 0%, respectively. None of the untreated cows had positive test results for beta-lactam antibiotics at any sampling time.


CONCLUSIONS
Penicillin was detected in milk for up to 22 hours after a single subconjunctival injection of procaine penicillin G in cows. This result should be considered when recommending milk withholding periods following the administration of penicillin by this route in lactating dairy cows.
Liljebjelke
K A
KA
Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Warnick
L D
LD
Witt
M F
MF
D000818:Animals; D002417:Cattle / Q000378:metabolism*; D003228:Conjunctiva; D005260:Female; D007267:Injections / Q000379:methods / Q000662:veterinary; D008892:Milk / Q000737:chemistry / Q000378:metabolism*; D010402:Penicillin G Procaine / Q000008:administration & dosage / Q000032:analysis / Q000493:pharmacokinetics*; D010406:Penicillins / Q000008:administration & dosage / Q000032:analysis / Q000493:pharmacokinetics*; D016037:Single-Blind Method
D010406:Penicillins; D010402:Penicillin G Procaine