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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

Forage Systems Update
Vol 14, No. 2

Over the past several months I have determined that we have done a poor job of educating you on how to manage your endophyte infected (E+) tall fescue pastures during the spring. All too often, I hear complaints about how poorly cattle are performing during the summer months, even though you are following a managed grazing system. After pinpointing exactly when cattle were moved off of E+ pastures, it becomes apparent that the cattle were moved off the E+ pastures too late. Typically, cattle are left on E+ pastures to graze through the month of June because "there is a ton of grass out there". In reality, E+ grass produced during the last half of May through June is the most toxic grass produced during the year. These toxins accumulate in cattle during May and June and with the onset of hot and humid weather (stress) the cattle just cannot perform.

Toxin concentration within the plant varies with the plant part and time of year. Highest concentrations are found in the seedhead, followed by the stem, and the lowest concentrations are found in leaf material. Seedheads can contain about a four times greater concentration of the toxin (ergovaline) than leaf blades, and about a twice as much toxin as stems. During late May tall fescue plants begin reproductive growth and stem elongation begins. Cattle will continue to readily graze the fescue at this time, but are ingesting a greater concentration of toxin. The problem only becomes worse with advances in plant maturity.

So what are you to do? Several options are available but all of them require you to start managing the toxin load your cattle are consuming. The first step is to test pastures for endophyte infection levels. Pastures recently tested at the FSRC have ranged from less than 5 % infection up to greater than 95% infection. As a rule of thumb, for every 10% increase in infection level you can expect steer average daily gain to decrease by approximately 0.1 lb/hd/day. For example, a pasture found to be 75% infected tall fescue will decrease ADG by 0.75 pounds when compared to an endophyte free pasture, and over a short 100 day period (valuing steers at $1.00/lb) this translates to a $75 loss/head. To avoid this loss cattle must be moved off of infected pastures as soon as the tall fescue begins reproductive growth (in northern Missouri this happens mid- to late May).

The best solution for highly infected fescue pastures, over the long run, is renovating pastures to endophyte free or novel endophyte cultivars. This is expensive and can take land out of season-long production for a year or more. When renovating pastures, we recommend using the spray-smother-spray technique. Briefly, this involves spraying the infected field with an effective herbicide, seeding an annual smother crop, and re-spraying prior to replanting the new forage. For spring seedings of the new perennial forage, the smother crop should be a winter annual small grain, for fall seedings of the new perennial forage, the preceding smother crop should be a summer annual (pearl millet, sudan...).

Other management options exist but implementing them every year is a necessity. These options include: livestock rotation to non-infected pastures beginning in late May, interseeding infected pastures with legumes and other grasses to "dilute" the infected fescue pasture, don't fertilize heavily with nitrogen in the spring, controlling seedheads and stems with clipping in mid- to late spring to reduce consumption of these plant parts by livestock, and feeding supplements to dilute the livestock diet. Although all of these management options work, it will probably take implementing several of them at the same time in order to attain livestock performance equal to what could have been attained by renovating pastures.

Most livestock farmers know that fescue toxicosis exists and have implemented corrective measures to help alleviate the problem. However, I would like to stress that many times we rotate cattle too late in spring to optimize the benefits of rotation. By rotating too late in the spring, livestock performance will suffer during the summer even though the livestock will not be eating highly toxic fescue during the summer months. This is because the toxin that is ingested in the spring accumulates in livestock and it takes time for the livestock to detoxify themselves. The best solution is to manage in such a manner as to not allow the livestock to consume the toxin in the first place.

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