Transfer of chlortetracycline from contaminated feedingstuff to cows' milk.
Three groups of four Friesian cows in mid-lactation were fed a compound feedingstuff contaminated with 2, 10 or 300 mg chlortetracycline/kg for 21 days, and were then fed an uncontaminated diet for seven days. A fourth group of four cows was fed an uncontaminated diet throughout the study. Daily pooled milk samples from each cow were analysed by high performance liquid chromatography (HPLC) with a detection limit of 50 microg chlortetracycline/litre. Chlortetracycline was detected in only two milk samples taken from one of the animals fed feed containing 300 mg 300 mg chlortetracycline/kg, and both contained less than the maximum residue limit (MRL) specified by the European Union (100 microg/litre). All the milk samples were also analysed by the Delvotest SP microbiological assay, which has a detection limit of 300 microg chlortetracycline/litre. During the treatment period, this method gave four presumptive false-positive results, because they were not confirmed by HPLC. Selected daily pooled samples from each treatment group were also analysed by the semi-quantitative Charm II radioreceptor assay with a detection limit of 10 microg chlortetracycline/litre. Immunoreactive chlortetracycline was detected only in the animals fed feed containing 300 mg chlortetracycline/kg and several of the results exceeded the EU MRL during the treatment period. No significant treatment effects on animal performance were observed. However, there was a trend towards a higher milk fat concentration (P<0.09) and a lower milk protein concentration (P<0.07) with increasing concentration of chlortetracycline in the diet.
McEvoy
J D
JD
Department of Agriculture for Northern Ireland, Stormont, Belfast.
Mayne
C S
CS
Higgins
H C
HC
Kennedy
D G
DG
D000284:Administration, Oral; D000821:Animal Feed; D000818:Animals; D000900:Anti-Bacterial Agents / Q000032:analysis*; D002417:Cattle / Q000502:physiology*; D002751:Chlortetracycline / Q000032:analysis*; D005260:Female; D005506:Food Contamination; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins
D000900:Anti-Bacterial Agents; D008894:Milk Proteins; D002751:Chlortetracycline