Ergovaline recovery from digested tall fescue seedheads

Authors: GOFF, B - University Of Kentucky; Aiken, Glen; WITT, W - University Of Kentucky

Submitted to: Kentucky Beef Report
Publication Type: Experiment Station
Publication Acceptance Date: 8/16/2012
Publication Date: 3/4/2013
Citation: Goff, B.M., Aiken, G.E., Witt, W.W. 2013. Ergovaline recovery from digested tall fescue seedheads. Kentucky Beef Report. Pgs. 9-10.

Interpretive Summary: Ergot alkaloids produced by the fungal endophyte that infects tall fescue are a frequent issue faced by cattle producers in the southeastern USA. These alkaloids have been shown to act as vasoconstrictors, and lead to the symptoms of fescue toxicosis. Ergovaline concentrations within the seedheads of tall fescue are known to be up to three times higher than within leaf tissue, which makes the reproductive growth of the grass a management concern. To further complicate matters, there are documented reports of steers and geldings selectively grazing these tissues when grazing tall fescue pastures at low stocking rates. While previous studies have estimated the release of alkaloids from plant tissues in the ruminant digestive system, the focus was primarily on vegetative tissues. An experiment was conducted to quantify the degree tall fescue seedheads were grazed upon by steers, and to estimate the amount of ergovaline. In pastures of toxic tall fescue, steers had grazed 78.8% of the seedheads. Seed heads were sampled weekly and shown to have organic matter digestibilities > 60% and nearly 100% of the ergovaline in seeds was released during in vitro digestion. Management strategies aimed at preventing reproductive growth in stands, such as heavy grazing, mowing, or chemical suppression, are needed to reduce losses in animal productivity. These management strategies could be useful to stocker producers for increasing efficiencies of backing beef cattle on toxic tall fescue pasture.

Technical Abstract: Seed heads typically contain high concentrations of ergot alkaloids, which makes them a highly toxic source of ergot alkaloids. Unfortunately, cattle selectively graze tall fescue seedheads. Seedheads were collected from pastures grazed by Angus-cross steers from early-May until mid-June. Pastures were also monitored at this time for the grazing of seedheads by the cattle. Samples were digested with two-stage acid-pepsin procedure, and the ergovaline concentration of all materials determined. Steers did not graze tall fescue seedheads until the first week of June, and removed portions from ~80% of the seedheads by mid-June. The percentage of the ergovaline released during digestion decreased slightly between early and mid-June (100 to 96%). However, the ergovaline concentration of the seedheads increased during this period (1.66 to 4.41 ppm), and resulted in a larger total amount of alkaloids that may potentially be absorbed by the animal. Management strategies that reduce the reproductive growth of tall fescue in pastures, such as mowing or grazing at high stocking densities, are necessary to reduce the effects of fescue toxicosis, as they prevent the consumption of plant tissues that contain high concentrations of ergot alkaloids, all of which are readily released into the rumen during digestion.