The significance of the ryegrass endophyte, Neotyphodium lolii, in Victorian pasture
Dr Kevin Reed
Department of Natural Resources and Environment
Pastoral and Veterinary Institute
Private Bag 105
Hamilton, Victoria 3300
In: Plant toxins and their effects on animal welfare. Paper presented at the Animal Welfare Centre Scientists' Meeting, 17th May 2002, Victorian Institute of Animal Science, Mickleham Road Attwood, Victoria.
Research conducted in Australia has established that the symbiont endophyte (Neotyphodium lolii) which resides within ryegrass - when compared to endophyte free perennial ryegrass - improves seedling vigour, tillering frequency, yield, pest tolerance and persistence. It has also been established that secondary metabolites produced by this micro fungus, known as the ryegrass endophyte, have had negative effects on the lamb-rearing ability of sheep and on the milk production of dairy cows.
With support from WestVic Dairy and NRE, surveys were conducted in SW Victoria during 1999 and 2000. On randomly selected pastures, perennial ryegrass always tested positive for endophyte. Ergovaline and lolitrem B were detected in perennial ryegrass. These are the most commonly studied toxic alkaloids associated with livestock health and performance on perennial ryegrass pasture. They were found to be above critical concentrations - as established by USA workers - on 1 in 3 farms during the February-April period. Lolitrem B remained above the critical level on 1 in 3 farms during the May-June period.
Relating the absolute alkaloid concentrations to data from animal production studies conducted in South Australia (by SARDI with DRDC support), France, Germany, Chile and New Zealand it is highly likely that ryegrass endophyte alkaloids cause significant economic losses from Victorian livestock whether or not clinical symptoms are apparent. Management solutions to eliminate toxins from the feedbase will be more readily adopted once comprehensive animal production systems are established to measure the nature and extent of differences in animal production, reproduction and welfare within the Victorian environment. Research is needed on the toxico-kinetics and dynamics of the ryegrass endophyte alkaloids in the animal.
The ryegrass endophyte
Perennial ryegrass (Lolium perenne) is the mainstay of temperate perennial pasture in Australia where 6,000,000 hectare have been sown to it. Research conducted by NRE has found that over 100 old pastures sampled from Victoria and New South Wales were all highly infected with the ryegrass endophyte, Neotyphodium lolii.
From work in New Zealand we know that the fungus Neotyphodium lolii is concentrated in that part of the plant considered most important for plant (and thus endophyte) survival, viz. the crown and reproductive tissue. Within individual tillers the lower leaf sheath contains the highest concentration of fungal mycelium.
Ryegrass endophyte alkaloids that affect livestock
NRE research has shown that the endophyte-infected perennial ryegrass plants from 100 old Australian pastures produce alkaloids including a vaso-constrictor, ergovaline and a tremorgen, lolitrem B. The concentration of these varies between different grass-endophyte associations. The relative importance of the grass and endophyte genetics has not been determined.
New Zealand workers report that the concentration of ergovaline follows a similar pattern to that of the endophyte with highest concentrations found in the crown and inflorescence. The concentration in the inflorescence can surpass that in the crown as the inflorescence matures. Ergovaline concentration may vary widely over the season and is significantly correlated with water stress in the host plant. Concentration of lolitrem B is high in the older tissues of the plant, increasing with leaf age. Large quantities of lolitrem B have been detected in old leaf sheath and dead leaf, while seed can account for nearly 60% of the total plant lolitrem B in mature plants. Lolitrem B concentration varies seasonally often peaking when the yield of green herbage is low; generally levels are lowest in late winter and early spring.
Alkaloid effects on livestock
Endophyte infected perennial ryegrass has a significant influence on several aspects of animal health and performance. Overt symptoms of ryegrass staggers - the most recognized syndrome - and heat stress occur spasmodically in herbivorous species grazing such pasture. Research in New Zealand has found that lolitrem B has a most disruptive impact on the digestive system. Toxin effects have not been reported on an industry basis in Australia, probably due to their spasmodic nature, and to the lack of association between presence of the endophyte and production penalties in the minds of producers.
The majority of clinically affected sheep recover spontaneously from ryegrass staggers but some die - either failing to regain mobility or from misadventure, e.g. falling into dams or creeks while in an uncoordinated state. In severe cases hundreds of sheep have died in single dam incidents. This maybe heat stress related, rather than misadventure, with the sheep seeking relief. In recent years the sub clinical effect of the toxins on animal performance has been examined at a number of research centres. NRE workers have reported significant increases in lamb mortality when ewes - that had experienced ryegrass staggers as weaners - grazed high endophyte pasture. Long-term depression of liveweight due to endophyte is likely to reduce reproductive efficiency. New Zealand, French and German workers have reported most significant reductions in the liveweight gain of lambs, increased heat stress in lambs and increased faecal contamination of wool leading to increased fly strike in lambs. Growth rate of lambs and hoggets has usually been improved by 20% to 100% in New Zealand experiments. Suckling lambs have similarly shown differences, particularly twins.
Whilst most work has been with sheep and lambs, similar trends may occur in cattle. In studies of cattle grazing endophyte-infected perennial ryegrass pasture, SARDI, New Zealand and South American workers have recorded reduced intake and/or milk production, and decreased liveweight, milk, butterfat and milk protein, and increased cell counts - and work with endophyte-infected tall fescue supports these findings. Cattle are affected similarly to sheep and dairy cows occasionally go down and may be difficult to move or milk. In the northland of New Zealand cows have had to be dried off due to ryegrass staggers, liveweight gain has fallen well below normal and young cattle have died. Milk production was increased 13% over three years in one study when cows were grazed on endophyte-free pasture over summer when compared to endophyte-infected pasture. These differences are sometimes associated with better performance of clover in low endophyte ryegrass pasture. Studies with beef heifers in Northland have recorded liveweight gain differences up to 7 kg/head over March-April - when perennial ryegrass pasture without endophyte was compared with endophyte-positive pasture. In all these New Zealand studies daily temperature rarely rose above 300C. The effects of endophyte-induced heat stress on livestock are likely to be greater in hot, humid situations where environmental conditions do not allow adequate dissipation of accumulated heat.
AgResearch have selected endophytes that do not produce toxic metabolites and these have now been inserted into modern New Zealand cultivars commercially available in Australia. Select endophytes have not been incorporated into Australian-adapted germplasm; seed that is free of endophyte is promoted by some companies. To benefit from seed bearing a select endophyte, we must eliminate seed of old varieties that contain wild endophyte. This will require considerable attention to land preparation, quarantine and paddock hygiene. Without such care the new population of select endophyte plants will rapidly become contaminated.
As experience with other pasture practices has shown, management solutions to eliminate neuro/vaso-constictor toxins from the feedbase will not be widely adopted until animal production experiments are established to measure the nature and extent of differences in animal production, reproduction and welfare - in the Victorian environment. Such work would form a basis for extension. In view of the relatively high concentrations of ryegrass endophyte alkaloids in our pasture, post-graduate study, undergraduate teaching and technology transfer activity concerning grass endophyte interactions and their significance needs to be developed.
As the adequate renovation of old pasture may take well over 20 years on many extensive properties, some research into how best to both minimize and overcome the impact of ryegrass endophyte alkaloids on livestock is desirable.
In Australia, some significant basic research on grass endophyte interactions is in progress at the CRC Molecular Plant Breeding where molecular marker systems are being developed at NRE's Plant Biotechnology Centre. This internationally significant work will determine the level of genetic variation within and between grass endophyte taxa and provide insight into the relationship between endophyte variation and variability in agronomic traits.
The Animal Welfare Science Centre was established by the University of Melbourne, Monash University and the Department of Primary Industries, Victoria. The Centre focuses and coordinates the research and academic resources of the three collaborating organisations, providing the animal industries, animal users, the farming community, Government, the general community and the academic community with an internationally competitive research, teaching and training resource in animal welfare.