Reading up on pasture forages tends to give one the distinct impression that having a field full of endophyte-infected fescue is not a good thing…but what is an endophyte? Why is it bad?
Simply put, an endophyte is a fungus that lives inside tall fescue. The fescue itself is in no way harmed by having a fungus between its cells. Quite the contrary. As far as the fescue and the endophyte are concerned, the arrangement is mutually beneficial. The endophyte could not survive in nature outside of a proper grass plant, so the fescue is a much-needed ally, providing the fungus with shelter and seed storage. In return for these services, the fescue receives chemical compounds called alkaloids, which provide the plant with resistance to insects, disease, and drought.
So far so good. Why, then, all the negative press about endophytes?
Another service that the endophyte provides the fescue with is protection from grazing animals. Not only are the alkaloids produced by endophytes something of a deterrent to mammals, they can also be harmful—even lethal—to livestock, most notably cattle and horses. Endophyte alkaloids constrict the blood vessels and reduce the circulation of animals that have ingested them, leading to serious complications. Affected cattle often show rough coats, intolerance to heat, poor weight gains, and reduced pregnancy rates. In winter, they may develop gangrene of the hooves, ears, and tail. Mares can experience life-threatening foaling difficulties, and any foals that do survive after being born may have weakened immune systems.
Once the effects of fescue on grazing animals were understood, scientists and plant breeders set to work removing the endophyte from the fescue. A number of methods are used to achieve this, including heat, humidity, and various chemicals. Because endophytes are transmitted through seed, a fescue plant that has had its endophytes killed in this manner can be used to produce subsequent generations of endophyte-free fescue. Over the years, different varieties of endophyte-free fescue have found their place in the offerings of companies selling pasture seed. Studies have proven that animals do indeed perform better on endophyte-free fescue pastures.
Unfortunately, removing the endophyte from the fescue has not been without consequences. By removing the fungus, plant breeders have also removed the fescue’s defense against insects and drought. It can be difficult to establish and maintain a good stand of endophyte-free fescue. However, careful pasture management and avoidance of overgrazing can prolong the stand’s lifespan to about nine years.
But since many ranchers do not want to deal with the establishment, maintenance, and reseeding of endophyte-free fescue pastures, scientists have since produced several strains of fescue containing only “novel” endophytes, fungi which increase the hardiness of fescue without producing toxic alkaloids. These new fescue strains are produced by inserting novel endophytes into endophyte-free fescue seedlings.
Research on the pros and cons of these varieties is still in the early stages. At this point, it appears that novel-endophyte fescue persists nearly as well as normal fescue while offering the improved animal performance of endophyte-free fescue. However, particular care may be required when storing seeds, as the novel endophyte can easily be killed by heat and humidity prior to planting.