CORVALLIS, Ore. – The Oregon State University Extension Service is warning livestock owners about potential problems if they use certain types of grass seed straw to replace hay in livestock feed.

The most significant problem, researchers say, is that turf varieties of tall fescue and perennial ryegrass may contain endophytes, which produce toxins that are harmful to livestock at high concentration levels.

Due to a regional shortage of hay this fall, livestock owners may turn to grass seed straw as a reasonably priced alternative for livestock forage. When the grass seed straw comes from unknown fields, however, it should be tested for the toxin level, according to Gene Pirelli, an OSU Extension livestock faculty member.

“It can then be mixed with other feeds, if necessary, to dilute the toxin to a safe level in the total ration,” Pirelli said.

Another problem is that grass seed straw may be lower in protein and energy than grass hay.

“Without proper supplementation,” Pirelli noted, “a diet of grass seed straw can lead to nutritional deficiencies, and the effects of endophyte toxins are even more severe in malnourished animals.”

Endophyte is a fungus that lives within the grass plant and benefits the plant by producing toxins that help fend off insects, diseases and grazing animals. Endophyte is transmitted through the seed, so a plant does not become infected from its neighbors. An endophyte-free grass variety will remain endophyte-free.

Different species of endophyte infect tall fescue and perennial ryegrass. The primary toxin produced in tall fescue constricts the blood vessels and reduces circulation to the body extremities. This interferes with the animals' ability to regulate body temperature in cold weather, causing a condition called "fescue foot," characterized by lameness and swelling in the legs, followed by tissue death at the tips of tail or ears and sloughing of the hooves.

Symptoms of fescue foot appear after 10 to 20 days of feeding on endophyte-infected tall fescue. Extreme cold increases the severity of the problem.

Horses are especially prone to developing serious reproductive abnormalities from endophytes in tall fescue, including failure to come into heat, early-term abortions, difficult births, retained placentas, poor udder development with little or no milk production and poor foal survival.

The primary toxin produced in perennial ryegrass causes a condition known as "ryegrass staggers" that can develop into severe tremors, incoordination and falling down. Symptoms of ryegrass staggers appear after seven to 14 days of feeding on endophtye-infected perennial ryegrass, but unlike with tall fescue, these symptoms disappear after the straw is removed from the diet.

All hay and pasture varieties produced in Oregon are endophyte-free or have very low levels. However, newer turf varieties are particularly high in endophyte because turf breeders have selected for the pest-resistant qualities that endophyte-infected plants have, qualities that reduce the need for pesticides while growing a lawn. These turf varieties make up most of the acreage of grass seed production.

No endophyte problems have been found with orchardgrass, bentgrass, or fine fescue straws.

When asked if there are safe levels of endophyte toxins for livestock, Morrie Craig, a professor in the OSU College of Veterinary Medicine, said that experiments have determined threshold levels below which clinical disease is not seen.

“These thresholds refer to the level of toxin in the total diet, not in single feed components,” Craig said. Forages with higher toxin levels may be fed safely, as long as they are diluted with other feedstuffs, he added.

Threshold levels of the tall fescue endophyte "ergovaline" are 400-750 parts per billion (ppb) for cattle; 500-800 ppb for sheep; and 300-500 ppb for horses, except for mares in the last 60-90 days of pregnancy, when the threshold is zero.

Threshold levels of the perennial ryegrass endophyte "lolitrem B" are 1,800-2,000 ppb for cattle and sheep. No threshold levels of this endophyte have been determined for horses.

The Endophyte Service Laboratory at Oregon State University tests forage samples for the level of ergovaline or lolitrem B endophytes. The cost is $40 per sample for either test.

For information on sampling for endophytes and a more complete discussion of endophyte toxicity, see the article: "Alert to Livestock Owners: Be Aware of Endophyte When Using Grass Seed Straw to Replace Hay in Livestock Feed" at

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Gene Pirelli,