Improved recovery of avoparcin from animal feedstuffs using a novel extraction method

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Abstract
Poor recovery of the glycopeptide antibiotic avoparcin from certain animal feedstuffs, e.g., dairy feeds, has been experienced by this laboratory and has been reported elsewhere. It is postulated that this may be due to binding of avoparcin to specific carbohydrate-binding glycoproteins, known as lectins, which are naturally present in feedstuffs. The effect of sample pre-treatment with sugar solutions on the recovery of avoparcin was assessed. Samples (n= 17) of a bovine finishing feed containing 20 mg kg–1 avoparcin were pre-soaked with water (control) or one of two different sugar solutions (sucrose or methyl-αD-mannopyranoside) prior to extraction. Increases in avoparcin recoveries relative to the controls (1.000) were (mean ± standard error of the mean) 1.18 ± 0.016 and 1.20 ± 0.036 for methyl-αD-mannopyranoside and sucrose, respectively. In a second experiment, replicate samples (n= 4) of 30 different feedingstuffs were pre-soaked with methyl-αD-mannopyranoside and compared with the official extraction method. Pre-soaking elevated the mean avoparcin determinations for all the bovine and avian feedstuffs and for four out of seven porcine feedstuffs. The increased concentrations detected were significant for dairy (17.44 versus 10.31 mg kg–1; P < 0.001) and beef finishing feeds (23.12 versus 19.53 mg kg–1; P < 0.01). These results provide a possible solution to the low recoveries of avoparcin experienced in the assay of dairy feeds.

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