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

Abstract

Low analytical recoveries of the glycopeptide antibiotic, avoparcin, have been observed in several types of compound animal feedingstuffs, particularly dairy and beef finishing feeds (Fagan et al., Analyst, 1995, 120, 2265). Individual compound rations contain different raw materials which vary in number and relative abundance. Any one of these feed constituents, or the interaction of several components may affect analytical recovery of the antibiotic. To investigate this theory, nine commonly used compound feed constituents 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 ration at 1, 3 and 90 d post mixing and the results were analysed by ANOVA. Overall, the recoveries of avoparcin from the different raw materials were very highly significantly different (P < 0.001) for both concentration and time. Maize gave the highest recovery, almost four times greater than that from soya. In general, increasing the amount of avoparcin added to feedingstuffs resulted in increasing analytical recovery, however percentage recovery decreased at the higher inclusion rates. Time also had significant effect on analytical recovery with concentrations measured on Day 1 and Day 3 being very highly significantly different from Day 90 (P < 0.001). It is concluded that the presence of specific raw materials in compound feedingstuffs will influence the analytical recovery of avoparcin.