Loline alkaloids : analysis and effects on sheep and pasture insects

Abstract

Loline alkaloids are commonly found in the endophyte-infected grasses tall fescue and meadow fescue (Festuca pratensis). In meadow fescue, lolines are often found in the absence of other alkaloids. The main objective of this research was to investigate the concentration and distribution of loline alkaloids in 12 meadow fescue lines and the effects of these loline alkaloids on two common pasture insects in New Zealand, grass grub (Costelytra zealandica) and Argentine stem weevil (Listronotus bonariensis), and sheep.

Samples of leaf and stem (6 times), crown and root (4 times), from twelve ecotype meadow fescues that originated from Europe were collected from plants grown in New Zealand during the years 2004 and 2005. Loline concentration was dependent on the presence of endophyte and varied independently between different parts of the plant and during seasons of the year. In general, concentration of loline in the stem > leaf > root. In stems and leaves, the loline concentration peaked at the second harvest in late spring but declined sharply at the third harvest. At the fourth harvest in early summer, the loline concentration increased in leaves but declined again thereafter. The loline concentration in the stems declined further after the third harvest and was lowest at the sixth harvest in late autumn. In crowns, there was no difference in loline concentration (p>0.05) between the lines but there was a difference between the harvest times (p<0.001) and a significant harvest time x line interaction (p<0.01). In roots, the loline concentration was extremely low in spring, increased slightly during the summer and peaked sharply in late autumn. Of the lolines, the concentration of N-formyl loline (NFL) >N-acetyl loline> N-acetyl norloline> N-methyl loline in all plant tissues measured. In general, each loline alkaloid as a proportion of NFL varied between different parts of the plant and in some lines.

In short term laboratory and field studies, grass grub larvae feeding on roots of endophyte infected meadow fescue containing lolines at concentrations >450 µg/g, either lost weight or gained less weight than the corresponding controls feeding on endophyte free or low loline grass lines. Loline concentrations in the roots of plants exposed to grass grub were significantly higher (p<0.001) compared to plants of the same line not exposed to grass grub at the expense of loline concentration in the crown (p<0.05).

Field and laboratory studies with Argentine stem weevil (ASW) also exhibited a reduction in feeding with less feeding holes in meadow fescue leaf in the presence of lolines compared with the absence of lolines. Total leaf loline concentration above a threshold of 400 µg/g significantly reduced (p<0.001) feeding damage to leaves in a dose dependent manner indicative of a protective effect of lolines to the plants from ASW.

Experiments with an acute (single 52 mg/kg BW dose) and chronic (68 mg/kg BW doses for 6 consecutive days) oral dosing of lambs with loline containing seed showed rapid metabolism and appearance of loline metabolites in urine within 30 minutes. The recovery of loline alkaloids from urine and faeces was low with 10% in acute and 4% in chronic studies. Blood parameters (red blood cell count, white blood cell count, haematocrit, and haemoglobin), four selected plasma enzymes (alkaline phosphatase, aspartate transaminase, creatine phosphokinase and gamma glutamyl transferase) and histopathological examination showed that lolines at such doses (selected to represent maximal exposure during grazing) were not toxic to sheep.

In conclusion, in the 12 endophyte infected meadow fescue lines that were studied, loline alkaloid concentration varied in stems, leaves, crowns and roots and during seasons of the year. Total loline concentrations >400 µg/g in leaves deterred feeding by ASW adults, and loline concentration >450 µg/g in roots deterred grass grub from feeding. Lolines at doses of potential maximal exposure from pasture grazing were nontoxic to sheep.