David Bransby, Jimmy Holliman, and Arturo Martinez

Most tall fescue (Festuca arundinacea) pastures in the United States contain a proportion of plants that are infected with an endophytic fungus, Acremonium neotyphodium. When this fungus is present in fescue plants, a complex of toxic chemical compounds known as ergot alkaloids is produced, and these toxins are more concentrated in the inflorescence, or seedhead of the plant, than in the leaves.

This has led some forage professionals to suggest that clipping the seedheads off infected fescue pastures in spring and early summer will reduce toxicity of these pastures to livestock. However, a recent study undertaken by the AAES indicated that the benefit from this management practice may be only marginal.

A grazing experiment was conducted at the Black Belt Research and Extension Center, Marion Junction. Tall fescue pastures that had more than 80% of the plants infected with the fungus were grazed by beef steers from March 11 to June 3, 1999, at a stocking rate of 1.5 animals per acre. The average weight of steers when grazing started was 765 pounds, and steers were weighed every 28 days.

Figure 1. Cattle grazing on clipped pasture at Black Belt Research and Extension Center.

There were six two-acre experimental pastures in the study. Each pasture was divided in half with an electric fence, and each half was grazed alternately for two weeks. This form of grazing management was employed because it would result in greater seedhead production than continuous or season-long stocking. Half of the pastures were kept virtually free of seedheads by mowing at a height of about eight inches from the ground prior to grazing.

The appearance of clipped pastures was distinctly better than that of pastures that were not mown, and signs of fescue toxicosis among animals, such as excessive salivation, appeared to be slightly more prominent on pastures that were not mown (figure 2). However, despite these apparent visual benefits from mowing, average daily gain over the 84-day grazing period for steers grazing the clipped pastures (2.53 pounds per day) was only marginally higher than for those grazing pastures that were not mown (2.31 pounds per day).

Figure 2. Excess salivation, a sign of fescue toxicosis, from a steer grazing unclipped pasture.

The difference in average daily gain over the experimental period translates into an advantage of 18.5 pounds per animal and 27.7 pounds per acre for clipped pasture. If this weight is valued at 70 cents per pound, income from the clipped pasture would be $19.40 more than for the pasture that was not mown. Given that pastures would need to be mown at least twice to achieve this benefit, the costs associated with mowing would likely be similar to the associated increase in income.

Therefore, based on this study, there was relatively little economic advantage in clipping seedheads off infected fescue pastures. However, data from grazing experiments can vary from year to year, so the experiment will be repeated to determine consistency of results.