The evaluation of endophyte toxin residues in sheep fat

To monitor changes in concentrations of lolitrem B and epoxy-janthitrems in the fat of sheep grazing perennial ryegrass infected with wild-type- and AR37-endophyte, respectively, during the time of year when ryegrass staggers would be expected to be observed.

Ten 5-month-old lambs with no previous exposure to endophytes were grazed on either wild-type (containing lolitrem B, n = 5) or AR37 (containing epoxy-janthitrems, n = 5) endophyte-infected perennial ryegrass (Lolium perenne L.) pastures between October 2008 and June 2009. Animals were regularly assessed for ryegrass staggers using the Keogh scale (0 = no signs, 5 = severe tremors). When a score of > 3.5 was observed animals were removed from the treatment pastures for 1 month. Fat biopsy samples were taken from each animal at approximately monthly intervals and analysed for endophyte metabolites using high performance liquid chromatography (HPLC) methods developed during this study. Regular herbage samples were also taken and concentrations of endophyte metabolites measured.

Efficient and reproducible methods to analyse both lolitrem B and epoxy-janthitrems in fat were developed. Concentrations of lolitrem B and epoxy-janthitrems in herbage and in sheep fat increased from late November to peak in mid-February. Ryegrass staggers was observed in both groups of sheep at this time. Following 1 month of grazing non-infected pasture mean concentrations in fat of lolitrem B decreased by 43% from 61.8 to 35.3 ppb, and of epoxy-janthitrems by 38% from 1032.0 to 639.5 ppb. Maximum concentrations in herbage of epoxy-janthitrems (35.7 ppm) were higher than of lolitrem B (3.4 ppm), but signs of staggers were less severe in sheep grazing pasture containing the former compared with the latter (median Keogh scores in late February were 2 and 3, respectively), consistent with epoxy-janthitrems being low potency toxins.

This study demonstrated that concentrations of epoxy-janthitrems and lolitrem B in sheep fat increased quickly during the initial phase of the study when concentrations in pasture increased, and decreased when animals were removed from pastures containing these compounds. These data will be used in the risk assessment of the endophyte metabolites.