Farm Tech

In The Paddock
Seasonal sheep flock management tips – January 2003

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Ryegrass endophytes – both friend and enemy

Key points

• Endophytes are fungi that exist inside plants.
• They produce a wide range of compounds. The main ones are peramine, lolitrem B and ergovaline.
• Peramine helps protect plants from insect attack, especially Argentine stem weevil.
• Lolitrem B is a neurotoxin that causes ryegrass staggers in animals.
• Ergovaline lowers blood prolactin levels and causes heat stress.
• Some of these chemicals, in combination with other as yet unidentified compounds, depress intake and liveweight gain, and cause scouring and dags in sheep.
• Non-toxic strains of endophyte have been identified.
• The most promising, AR1, produces peramine and is commercially available. It protects the plant from insect attack and has no ill-effects on grazing animals.

Endophytes are fungi that grow inside plants in a symbiotic relationship.

Beneficial effects include the protection they give grasses from attack by some insects, nematodes, and plant diseases.

They can make their hosts more drought-tolerant and in some plants, can trigger enhanced growth and tillering. Their presence may also discourage over-grazing by mammals.

Negative effects include the production of alkaloids which affect the health and production of grazing animals.

Effects on pasture growth and yield

Endophytes are essential because they protect ryegrass from pests, notably Argentine stem weevil (ASW). In 1991, this pest was estimated to be costing New Zealand $46-200 million in pasture damage each year.

Endophytes also protect perennial ryegrass from other invertebrates, such as black beetle, which in some seasons can be a serious pest in northern New Zealand.

Endophyte-free ryegrass can be quickly destroyed by black beetle. If endophyte is present, feeding by adult beetles is deterred, and egg and larval numbers are reduced.

Ryegrass has greater tolerance to stresses like drought when infected with endophyte. It's also less likely to be severely grazed. And most importantly, endophyte-infected ryegrass pastures produce more dry matter than endophyte-free pastures.

On the down-side, clover growth tends to be poorer in endophyte-infected pasture. This effect may be compounded by the tendency for livestock to preferentially graze clover in a mixed sward and actively avoid the infected ryegrass.

Before 1980, it was thought that a fungus was involved with ryegrass staggers, and research aimed to isolate the chemical(s) responsible. The discovery of endophytes hastened this process.

Several related compounds were identified, and of these, lolitrem B proved to be the most abundant and most potent. The main compound responsible for protection from ASW was shown to be peramine.

Ergovaline was also found. This lowers blood prolactin levels, causing a host of animal health problems including heat stress. Ergovaline and lolitrem B also protect against insect pests.

Because the endophyte and the host have evolved together, there is an array of compounds present in endophyte-infected grasses. These may be a cause of scouring, dags and other symptoms of ill-thrift in stock.

In the laboratory, it is possible to select or develop endophyte strains with varying levels – as low as nil – of particular alkaloids.

Endophyte strains have been identified which produce peramine but are free of ergovaline and/or lolitrem B. The novel endophyte (AR1) is one of these.

AR1, which is produced by AgResearch, significantly reduces the risk of animal health problems. Trials show animal performance on AR1 pastures to be similar to those on endophyte-free pasture.

More information

Ryegrass endophyte – an up-to-date review of its effects, WoolPro Report, 2001.

Your local farm consultant or veterinarian can provide useful advice about ryegrass endophytes. Alternatively, contact your local Meat & Wool Innovation specialist: