Tall fescue is a commonly grown forage for cattle, particularly in the southeastern and lower midwest states, as well as the Pacific northwest. This grass originally came from Europe and was discovered growing in a few isolated stands in the U.S. in the early 1930’s. It was recognized as being easy to establish with a long growing season, resistant to drought and insects, and able to grow on many types of soil. However, it was soon discovered that cattle performance was negatively affected by the grass.
Today, we know that a high percentage of tall fescue pastures are infected with a fungus that grows inside the plant (so it is not visible to the eye) and the fungus produces a number of chemicals that provide both the positive and negative attributes of the grass. Not all fescue pastures are infected with endophyte fungus, and the percentage of plants in a given pasture that are infected will vary from one pasture to another. Generally speaking, the greater the percentage of plants infested with the fungus in a pasture, the greater the negative effects of fescue toxicosis. Although the fungus is found throughout the tall fescue plant, it is found in the highest concentration in the seed head and stems with lesser concentrations in the leaves. The fungus can be spread to un-infected pastures if infected seeds blow or are transported to bare ground where it can become established.
Cattle grazing heavily infected stands will consume less grass, gain less weight, and have lower pregnancy rates than cattle grazing other types of forage. Cattle with fescue toxicosis syndrome are often recognized by having a rough, long haircoat and being thin. In addition, severely affected cattle will have high body temperature, and they will attempt to cool themselves by standing in water and seeking shade. Blood flow to the feet, tail switch, and ears is reduced, and in cold weather, affected cattle can slough the ends of their tails and the tips of their ears and in some cases, even the hooves can slough.
Cattlemen with infected tall fescue pastures have a number of options. In many situations, because of fescue’s positive properties, they may choose to live with it and work to reduce the negative effects by inter-seeding legumes into the pasture to dilute the intake of fescue. In addition, if other types of forage are available, cattle can be moved off of infected pastures during the summer months when the effects are most severe. If fescue is grazed heavily so that the plants are kept short, less endophyte fungus will be present in each bite of grass. Grain supplementation also acts to dilute the amount of endophyte consumed. Cows fed grain along with highly infected fescue hay had reduced winter weight loss and improved pregnancy rates compared to cows fed infected hay alone.
Some producers may decide to invest the resources necessary to avoid the endophyte completely by replanting infected stands of tall fescue with non-infected varieties of fescue or other grasses. There are endophyte-free as well as novel-endophyte varieties of tall fescue that can be used to replace the endophyte infested stand. The novel-endophyte varieties are infected with strains of fungus that provide some of the beneficial effects with few of the detrimental effects.
Attempts to reduce the effects of the endophyte fungus through feed additives or treatments applied to the cattle have not consistently shown benefits. However, it is recommended that cattle grazing infected fescue not be additionally stressed by heavy parasite loads, mineral deficiencies, or other disease. The best approach to managing fescue so that the negative effects of the endophyte are minimized will depend on your local conditions. By working closely with area extension and agronomy specialists, you can develop a plan for coping with this problem.