Assessment of antimicrobial transfer from treated to untreated mammary gland quarters by use of high-pressure liquid chromatography for detection of cloxacillin in milk samples from nonlactating dairy cows.
OBJECTIVE
To determine whether half-udder intramammary infusion of cloxacillin results in transfer of cloxacillin from treated to untreated mammary gland quarters within nonlactating cows, and, if so, at what concentrations, and to determine whether selection of ipsilateral versus diagonal-contralateral quarters for treatment affects cloxacillin transfer among quarters.


METHODS
20 Holstein-Friesian cows from a dairy herd.


METHODS
A within-cow half-udder comparison trial was used in which 2 of 4 mammary gland quarters (ipsilaterally or diagonally) received an intramammary infusion of cloxacillin on day 1 of the nonlactating period. Three days later, milk samples were taken from all untreated quarters and high-pressure liquid chromatography was used to detect and quantify milk cloxacillin concentrations.


RESULTS
Cloxacillin was detected in 25% of all untreated mammary gland quarters. Mean cloxacillin concentration in untreated quarters was below minimum inhibitory concentrations for targeted mastitis pathogens. No significant difference in cloxacillin concentrations was found in the ipsilateral or diagonal treatment groups.


CONCLUSIONS
Within-cow half-udder comparison trials are valid for antimicrobial trials in nonlactating cows, although transfer of antimicrobials does occur in trace concentrations. Ipsilateral or diagonal-contralateral treatment designs perform similarly. This type of design is economical for researchers, although care must be taken to account for within-cow clustering of mammary gland quarter data.
Sanford
Carolyn J
CJ
Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Canada.
Keefe
Greg P
GP
Dohoo
Ian R
IR
Leslie
Ken E
KE
D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis* / Q000493:pharmacokinetics*; D002417:Cattle / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003023:Cloxacillin / Q000032:analysis* / Q000493:pharmacokinetics*; D005260:Female; D007774:Lactation; D008321:Mammary Glands, Animal / Q000378:metabolism*; D014018:Tissue Distribution
D000900:Anti-Bacterial Agents; D003023:Cloxacillin