The effect of Acremonium loliae on ram lambs

Animal and pasture productivity is known to be altered by the infection of perennial ryegrass (Lolium perenne L.) pastures with the endophytic fungus Acremonium loliae. Rams grazing ryegrass pastures infected with A. loliae have been associated with reduced liveweight gains, lowered serum testosterone and prolactin concentrations, and increased faecal soiling. Species and sire variations to ryegrass staggers susceptibility have been reported, suggesting that genotype effect may exist. Recent research has started to focus on other toxic compounds that may be responsible for some of the effects associated with endophyte infected ryegrass ingestion. The trial consisted of two groups of 32 coopworth ram lambs balanced for sire and liveweight, rotationally grazed on high endophyte (+E) Nui ryegrass and low endophyte (-E) Nui ryegrass. The experiment ran from the 14th March to 10th June 1991, a total of 12 weeks. Pasture intakes were kept similar throughout the trial period, and animal performance was regularly monitored. Throughout the trial, liveweights, testis (anterior-posterior [AP]) diameters, ryegrass stagger scores, faecal moisture and dag scores were recorded and blood samples taken. Blood plasmas were analysed for testosterone, prolactin, aspartate aminotransferase (AST), total protein, and albumin content. The result from this experiment clearly show a relationship between the +E ryegrass pastures and ryegrass staggers, increased faecal soiling and faecal moistures. No significant Iiveweight or testicular AP diameter differences were recorded over the trial period. Pasture intakes by both treatment groups were low and similar in quantity. This was probably responsible for the lack of significant liveweight and testicular diameter differences. A high concentration and incidence of endophyte hyphae was found in the high endophyte ryegrass which related to the severe clinical ryegrass stagger signs observed. Prolactin and total protein concentrations were significantly depressed in rams grazing +E ryegrass, while albumin, AST, and testosterone were unaffected. The rams grazing +E ryegrass were therefore hypoglobulinaemic suggesting the immune system may have been affected. As AST and albumin levels were unaltered by ryegrass staggers, suggesting that lolitrems may not cause liver damage as previously suggested. Peramines and ergopeptine alkaloids are known to occur in varying concentrations in +E ryegrasses. Ergovaline is known to be associated with depressed prolactin concentrations and the thermoregulatory disorder fescue toxicoses. Therefore, these toxic compounds or some other unknown compounds may be responsible for liver damage and depressed hormone effects associated with endophyte ingestion.