A study of the effect of individual feed constituents on the recovery of avoparcin from compound animal feedingstuffs

Low analytical recoveries of the glycopeptide antibiotic, avoparcin. have b een observed in several types of compound animal feedingstuffs, particularl y dairy and beef finishing feeds (Fagan et al., Analyst, 1995, 120, 2265). individual compound rations contain different raw materials which vary in n umber and relative abundance. Any one of these feed constituents, or the in teraction of several components may affect analytical recovery of the antib iotic. To investigate this theory, nine commonly used compound feed constit uents were mixed:with a commercially available avoparcin feed supplement to give four final avoparcin, concentrations covering the range of inclusion rates (0-20 mg kg(-1)). Triplicate determinations were performed on each ra tion at 1, 3 and 90 d post mixing and the results were analysed by ANOVA. O verall, the recoveries of avoparcin from the different raw materials were v ery highly significantly different (P < 0.001) for both concentration and t ime. Maize gave the highest recovery, almost four times greater than that f rom soya. In general, increasing the amount of avoparcin added to feedingst uffs resulted in increasing analytical recovery, however percentage recover y decreased at the higher inclusion rates. Time also had significant effect on analytical recovery with concentrations measured on Day 1 and Day 3 bei ng very highly significantly different from Day 90 (P < 0.001). It is concl uded that the presence of specific raw materials in compound feedingstuffs will influence the analytical recovery of avoparcin.