Tall Fescue Toxicity Leads to the Development of 'Max Q'
Of all the major cool-season perennial grasses used in the United States, including eastern Oklahoma and Texas, the one grown on the most land area is tall fescue. The majority of this acreage (by some estimates, more than 40 million acres) is naturally infected with a fungal endophyte. Its scientific name is Neotyphodium coenophialum, but it is better known by farmers as simply "the endophyte" (Photo 1).
The main tall fescue variety used throughout the country is still Kentucky 31, which was released in 1943. When infected with its native endophyte, the growth, survival, drought tolerance and competitiveness of Kentucky 31 is enhanced (Photo 2). Richard Shelby of Auburn University demonstrated the immense practical impact of endophyte infection in a 1991 survey that found pastures presumed to be free of the endophyte demonstrated increasing levels of endophyte infestation of 4 percent per year for nine to 12 years. The increased infection percentage was attributed to better survival of infected plants in mixed stands during hot, dry summers.
However, endophyte infection leads to "fescue toxicosis" in grazing animals. This condition is a result of ingestion of ergot alkaloids derived from the endophyte association. This toxicity is generally characterized by poor weight gain and reproduction in animals consuming the forage. Although the most common visual symptom is animals trying to cool their elevated body temperatures in ponds or defecation wallows, the negative effects of fescue toxicity on animal gains are striking and economically significant (shown in Table 1).
The toxicity of endophyte-infected (E+) tall fescue, therefore, presents livestock producers with the dilemma of whether to grow E+ varieties for stand persistence, risking reduced animal performance because of the inherent toxins. Since the vast majority of U.S. acreage including newly planted pastures is E+, most producers have decided stand persistence, and not fescue toxicosis, is the most important consideration in their operation.
In a survey by Lacefield, Ball and Henning in 1993, 80 percent of current tall fescue acreage was infected with the endophyte at a mean infection rate of 76 percent, and 50 percent of the respondents considered their new plantings with endophyte-free (E-) varieties to be failures. In the same survey, it was found that the main reasons farmers do not convert to E- pastures were lack of confidence in E- varieties and a perception that the benefits do not outweigh cost. The failure of E- varieties to assume a substantial share of the tall fescue seed market also supports this view. It goes without saying, therefore, that most livestock grazing tall fescue pastures in the United States probably suffer from some degree of fescue toxicosis.
Two general approaches are being pursued to overcome the fescue toxicosis problem: one is management of both pastures and animals to reduce toxicity in current E+ pastures and the other is development of persistent varieties with nil production of the problem ergot alkaloids.
Management of pastures and animal
For pasture management, the following options are currently used by producers: using E- tall fescue varieties with good summer management (rest); close grazing and periodic clipping of E+ forage to remove seedheads; use of pastures and/or hay of different forage species (i.e. bermudagrass) during vulnerable periods; and inter-planting E+ pastures with other forages. All are practiced to some degree, but the one with the greatest use and potential is inter-planting with legumes (clovers, alfalfa, etc.). The ability of even small amounts of legume to increase animal performance of E+ pastures can be seen in Table 1. In this example, the addition of only 22 percent of the available forage supply as alfalfa increased animal gain 50 percent over the E+ alone pasture. However, even though animals are gaining better, they are still experiencing symptoms of fescue toxicity as demonstrated by the lower gains of the E+ fescue/alfalfa pastures compared to the E- pastures.
For very sensitive animals such as horses, especially pregnant mares, complete removal from tall fescue pastures is the only recommended option. Direct treatment for relief of fescue toxicosis in less-sensitive animals such as beef cattle has concentrated on the following: feed treatment and additives such as ammoniation of hay or supplementation with thiamin, selenium and copper, seaweed extract, etc.; pharmaceuticals such as metoclopramide, domperidone, etc.; immunologic protection with anti-ergot sera; and animal breeding and selection for better performance when grazing toxic tall fescue forage. Of these, pharmaceuticals, especially domperidone, have shown the most promise. Again, it should be emphasized that animals are still suffering from toxicosis and these treatments only alleviate some of the symptoms and not the main cause, which is the toxic fescue pasture itself.
Development of MaxQ Tall Fescue
Development of E- cultivars persistent enough for the expectations of most livestock producers has not been successful to date, but is still being pursued by both private and public plant breeders, including Andy Hopkins here at the Noble Research Institute. Genetic manipulation of the current toxic endophytes themselves is progressing, but limited effort and technical demands inherent in the work have not resulted in strains re-engineered to be non-toxic available for re-infection. However, it was the strategy of isolating naturally-occurring, non-toxic endophyte strains and re-infecting these strains into elite varieties that led to the commercialization of "MaxQ" tall fescue. MaxQ is actually a non-ergot, alkaloid-producing endophyte strain currently re-infected into the tall fescue varieties Jesup and Georgia 5.
In proof-of-concept studies between the University of Georgia and AgResearch, New Zealand, MaxQ was found to provide better animal performance (Table 2) than E+ tall fescue and better stand survival than E- tall fescue (MaxQ survival is similar to the E+ Ky 31 in Photo 2). With cows and calves at weaning, cow body condition scores were higher, and calves were 50 pounds heavier on MaxQ pastures compared to toxic E+ pastures. For stockers, average daily gains favored animals grazing MaxQ over E+ forages with these MaxQ gains comparable to contemporaries on E- pastures. Hopkins and Jim Johnson have recently found similar pasture stocker performance with MaxQ at the Foundation's Red River farm. There also appeared to be some carryover of toxicosis into the feedlot as animals from E+ pastures continued with lower gains in the Georgia trials (Table 2). At no time with all studies to date have animals grazing MaxQ, including lambs and horses, showed classic fescue toxicosis symptoms.
Tall fescue pastures in the United States will continue to be dominated by plants infected with toxic Neotyphodium endophytes. Research and extension efforts that allow producers to better deal with toxicity will need to continue. This will include pasture and animal management to directly relieve toxicity problems. The future will also involve variety and/or endophyte improvement to eliminate the toxic effects but retain the beneficial agronomic performance of the current associations. The use of naturally-occurring strains like MaxQ is the latest effort to help with this and will need to be watched closely for its on-farm success.