Fescue toxicity is the costliest grass-related disease in the United States. Cattle consuming endophyte-infected fescue experience production losses exceeding $600 million per year. Fescue is commonly grown throughout the mid-western and southern United States and accounts for over 40 million acres of forage land. Tall fescue has long been associated with a syndrome known as fescue toxicosis (a.k.a. Fescue Foot or Summer Slump). An endophyte fungus within the fescue plant causes fescue toxicosis. This endophyte produces alkaloids that cause adverse symptoms in grazing livestock including: decreased weight gains, weight loss, decreased feed intake, reduced milk production, higher body temperature, increased respiration rates, rough hair coat, unthrifty appearance, loss of blood flow to extremities and poor reproductive performance. Symptoms seem to be exacerbated during very warm or cold temperatures. Table 1 illustrates the differences in weight gain in steers on both high- and low-endophyte fescue diets.
It is important to understand the symbiotic relationship between the endophyte and tall fescue plant. The endophyte is spread via infection of the seed. Endophyte-infected plants cannot infect non-infected plants. When the infected seed germinates, the endophyte grows too and spreads throughout the plant from the base up. Once the plant enters its reproductive stage, the endophyte moves into the stem and concentrates in the seeds.
Endophyte-infected fescue can take over a stand when non-infected plants thin giving the endophyte-infected plants a chance to establish. Superior adaptability will often allow the endophyte-infected fescue to out-perform non-infected fescue. It is impossible to visually identify which plants contain the endophyte. However, there are several laboratories across the country that will test for the presence of endophyte.
With this in mind, you might ask yourself why not just grow endophyte-free or low-endophyte fescue? There are certainly endophyte-free and low-endophyte varieties of fescue available. However, it is not an easy decision to switch from endophyte-infected fescue. The endophyte-infected fescue has a significant competitive advantage and it is very costly to reestablish new pastures. Because endophyte-infected fescue is quite hearty and tolerant to drought, overgrazing, insects and diseases, it is still abundant in many areas. As a result, fescue toxicity symptoms are still a very real concern for livestock producers in areas where fescue is abundant.
Dealing with Fescue Toxicity via Technology
Research has shown that copper levels are lower in endophyte-infected fescue vs. endophyte-free fescue when grown under identical conditions. These differences are most pronounced late in the growing season (See Table 2). These findings support observations of decreased copper status in cattle grazing infected fescue. In research conducted in Virginia, cattle grazing endophyte-infected fescue exhibited decreased copper status as opposed to cattle grazing endophyte-free fescue. However, the magnitude of this decrease was greater than the difference between the forages. This demonstrates that the endophyte not only decreases the total amount of copper present in the fescue, but also, negatively affects bioavailability of copper for the animal. This makes sense when you consider that the typical symptoms for fescue toxicosis closely resemble those for copper deficiency. These symptoms include rough, discolored hair coats; winter coats that are slow to shed out; decreased conception rates; increased days open; hoof problems; and depressed immunity. For all of these reasons, lowered copper status plays a large part in the fescue toxicosis syndrome. Proper supplementation with a high copper supplement can help alleviate some of the fescue toxicity symptoms.
Research has also shown that the body utilizes copper better in the presence of zinc. Zinc and copper interact within the body much as calcium and phosphorus interact. Similarly, the ratio of zinc to copper is as important as the absolute levels of either copper or zinc. Ideally the proper ratio of zinc to copper is from 3:1 to 5:1 to maintain optimum mineral absorption of both minerals.
Most fescue is grown in areas that contain antagonistically high levels of sulfur, molybdenum or iron. Sulfur, molybdenum and iron bind up copper making it unavailable to the animal. Also, extensive feeding of DDGS, which is high in sulfur, can contribute to lowering copper availability for livestock.
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