Agronomy Guide
Cooperative Extension Service, Purdue University, West Lafayette, Indiana
(Forages) AY-258
minimizing Tall Fescue Toxicity
Keith D. Johnson,
Department of Agronomy, Purdue University
Tall fescue is one of the major cool-season grasses grown in Indiana. Agronomically, tall fescue is an excellent forage crop. The crop responds well to fertilization, has excellent seedling vigor, can withstand heavy grazing pressure, has a massive root system that aids in erosion control, survives drought and flood, and can be stockpiled for winter grazing. Laboratory analyses also indicate that tall fescue is as high in quality as other cool-season grasses such as orchardgrass and smooth bromegrass.
Unfortunately, because of tall fescue toxicosis much of the benefit of the grass’s superior agronomic characteristics is wasted. Ruminant livestock and horses seldom have performed as well on tall fescue as they have on other cool-season forages. Livestock have been noted to exhibit one or more of the following symptoms when consuming tall fescue pasture or hay: nervousness, rough hair coat, elevated body temperature, reduced forage intake and weight gain, low conception rate, excessive salivation, higher respiration rates, greater water consumption and urine volume, reduced milk production, and more time spent in the shade.
PROBABLE TOXIN SOURCE
There is new information, however, that promises to redeem tall fescue’s lowly status in livestock circles. Researchers at the University of Georgia believe they have succeeded in isolating the cause of the toxin that has given livestock performance problems. Prompted by earlier work done in New Zealand, the Georgia scientists identified the endophytic fungus Acremonium coenophialium in pastures where fescue toxicosis had been experienced.
Subsequent research at other universities supports the Georgia findings. A long-term study at Auburn University found that there were more grazing days per acre when the herbage was fungus-infected than when it was fungus-free. Cattle found the infected forage less palatable and, therefore, consumed less forage. Calves grazing infected pasture had temperatures approximately 2°F greater than calves grazing fungus-free pasture, and the average daily gain was 0.82 pound higher on the fungus-free pasture (Table 1). Significant research data from the University of Kentucky indicates that cattle have depressed gains and elevated body temperatures when grazing fungus-infected pastures in mid-summer and late-fall or when fed fungus-infected hay (Tables 2-4).
METHOD OF TRANSMISSION
Acremonium coenophialium is an endophytic fungus, that is, a fungus that lives within a plant's intercellular spaces. The endopytic fungus overwinters within the plant itself, and fungus growth occurs in the spring as tiller growth resumes on the fescue plant. The seed head becomes infected, the seed acquiring the endophytic fungus. Since the primary means of transmission is the seed source itself, this explains why a large percentage of the fescue pastures are infected.
The fungus does not appear to move quickly from an infected area to a bordering non-infected area, however. This is encouraging for producers who have never planted tall fescue before and are able to find a low-endophyte seed source.