Tall fescue is a useful perennial forage grass for Iowa. It is adapted to a wide number of soils, has a long growing season, and is suitable for use in mixtures with other forage grasses and legumes. Unfortunately, many of the tall fescue plants in Iowa pastures harbor a fungus (called an endophyte) that can cause nutritional and physiological problems for livestock grazing these pastures.
The presence of the endophyte fungus is actually an advantage to the fescue plants; it improves their vigor. It imparts an increased resistance to insects and diseases and improves the plants' tolerance to heat and soil moisture deficit. However, the alkaloid(s) associated with the endophyte fungus acts as a restrictor of blood flow in livestock. A group of alkaloid-related physiological conditions, sometimes called "fescue toxicosis" or "summer syndrome," can occur in the summer associated with livestock grazing endophyte-infected fescue. Symptoms in cattle are rough hair coats, poor rates of gain, poor conception rates, and high body temperatures, characterized by animals staying in shade or standing in water, even on average or cool days.
A group of reproductive problems are a particular concern in mares grazing in pastures containing endophyte-infected fescue plants. Loss of ear tips and tail switches are the most common symptom of poor circulation in cattle grazing endophyte-infected fescue in the winter months.
The fungus and the highest concentration of alkaloid are present in the developing seed stem, seed head, and developing seed of the fescue plants. So spring and summer fescue management should focus on managing the seed stems in the pasture. Early, close grazing reduces seed stem growth, and promotes leafy regrowth. An important management step now is to clip off the emerged seed stems of fescue pastures. As the summer progresses, moving livestock to non-fescue forage sources is recommended.
The endophyte and alkaloid also may be present in fescue being harvested as hay. Research is showing that the concentration of the alkaloid will decline by about half during the hay-curing process, but it does not go away completely.
Fields can be sampled and tested for the endophyte. And, based on existing livestock problems and the degree of infection, fescue pastures can be managed by interseeding other forages, in an effort to dilute the alkaloid intake, or by complete stand renovation.
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Leaf features (left) help to identify tall fescue in the field. Mature tall fescue seed heads (right). (Photo [left], Stephen K. Barnhart)
This article originally appeared on pages 157-158 of the IC-496(14) -- June 5, 2006 issue.