Toxins in endophyte infected perennial grasses	AG0863
Kevin Reed, Hamilton November, 1999

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Toxins are produced in perennial ryegrass only if it is infected with the common endophyte (a fungus), Neotyphodium lolii. In most old pasture about 90% of perennial ryegrass plants are infected. The plants signal the endophyte to produce secondary metabolites depending on the conditions/stress on the plant. Some of these include the toxins described below which can impact on the performance and health of most species of livestock. For further information refer to related Agriculture Notes:

AG0202: Endophyte in perennial grasses - its effects on host plants and livestock, and AG0700: Perennial ryegrass staggers/ill thrift.

Lolitrem B
Lolitrem B is a major cause of ryegrass staggers in horses, cattle, sheep, deer, alpaca and various other species of herbivorous mammals. It is concentrated in older tissue, at the base of the plant, and in seed. Often when the yield of pasture on offer is low, animals graze the crown of the plant where the lolitrem B concentration is high. The lolitrem B concentration increases when the plant is stressed for moisture, and when soil nitrogen is high.

Erogovaline
Erogovaline causes reduced intake and heat stress in livestock, depresses production of the hormone, prolactin, and is suspected of lowering reproductive efficiency. It also affects the motility and secretory powers of the gastro-intestinal tract so that water secretion is reduced. This results, for example, in scouring in cattle and dags on sheep. It deters the pasture insect pest, African black beetle (Heteronychus arator) which is a problem in maize crops, pasture and turf – mainly in NSW and WA. Like lolitrem B, the concentration of ergovaline is also increased when the plant is stressed for moisture, and when soil nitrogen is high. Ergovalinine, an epimer or similar molecule to ergovaline; is also determined in the toxicology laboratory and the two are added together to estimate effective ergovaline because ergovalinine readily converts to ergovaline.

Ergovaline is also produced in tall fescue if that grass is infected with the endophyte, Neotyphodium coenophialum. Approved pasture cultivars of tall fescue, Demeter, AU Triumph and Fraydo, do not contain this endophyte, however many overseas cultivars and cultivars developed mainly for use in turf do contain the endophyte.

Peramine
Peramine deters a wide range of insects but is not thought to be particularly effective on the main Victorian insect pests. It has no apparent direct effect on livestock. The subclinical effects of ryegrass toxins on livestock are not fully understood, but can impact on intake, milk production, behaviour and possibly reproductive performance. The presence and type of endophyte can also be controlled. In the future, cultivars with low toxin concentrations for use in pasture, or, toxin binding products that can be fed to livestock, may become available.

Analysis of toxins in herbage samples

The Pastoral and Veterinary Institute in Hamilton provides a commercial analytical service. Samples of pasture, hay, silage, seed or straw may be tested. Samples should be collected and packed following a protocol - provided by the Institute on request. Ergovaline concentrations typically lie within the range, 0 to 1.5 mg/kg, occasionally concentrations up to 8 mg/kg maybe recorded. Lolitrem B concentrations are typically 0 to 3 mg/kg but rise on occasions to concentrations up to 6 mg/kg. Peramine concentrations are typically between 0 and 50 mg/kg.

Use care in interpreting toxin concentration data

Endophyte frequency
The toxin concentration results from the laboratory analysis relate to that particular paddock/forage sample at that time. It is in no way an endorsement for or against the cultivar of perennial ryegrass last sown in that paddock. We cannot assume that because a ryegrass toxin concentration is reported as low, that this cultivar of perennial ryegrass will always be low. Toxin concentrations are influenced by both grass and endophyte genetics, by environmental conditions and by the proportion of the grass plants that are infected (this is referred to as endophyte frequency). Some new pasture that has been sown with old seed may have a low infection frequency. This may rise sharply over 2-3 years depending on how well resident seed has been eliminated from the environment.

Critical levels
The important factor is the total toxin intake rather than the concentration in the grass. The intake of toxin may be diluted with supplementary feed/fodder crops etc. – but not necessarily with hay/silage made from endophyte infected perennial ryegrass. Most research workers regard 0.4 – 0.8 mg/kg ergovaline in the diet and 1.8 mg/kg lolitrem B, as threshold concentrations for cattle. Concentrations of 0.2-0.3 mg/kg however have caused measurable changes in physiological functions and are considered likely to cause sub clinical effects on livestock performance.

Various herbivorous mammals are affected by ryegrass endophyte toxins and threshold concentrations vary with animal species. Within species, individual animals differ in their response to the toxin. In the USA the threshold levels of ergovaline are given as 0.3-0.5 mg/kg ergovaline for horses and 0.8-1.2 mg/kg for sheep. Some other species, for example Alpaca, may have lower thresholds.

Important sub-clinical effects may occur in cattle grazing grass containing lower than these threshold concentrations of toxin. South Australian research has found that during March, when lolitrem B averaged 0.2 ppm, milk yield from irrigated perennial ryegrass was lower by 12% on endophyte infected ryegrass compared to endophyte free ryegrass.

At or above the threshold concentration, clinical symptoms may be observed where the ryegrass forms the major source of the cow's diet. Hay and silage may also be toxic. In the USA relatively low ergovaline concentrations in grass hay can cause clinical symptoms in stall-fed steers. Work in New Zealand has found that where silage was made from endophyte infected ryegrass, milk production was lowered significantly.

Contacts

The Pastoral and Veterinary Institute
Private Bag 105
Hamilton VIC 3300
Ph. (03) 5573 0900

The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.