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United States Department of Agriculture

Agricultural Research Service

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Location: Dale Bumpers Small Farms Research Center

2013 Annual Report

1a. Objectives (from AD-416):
The overall objective of this research is to minimize economic losses from fescue toxicosis. Specific objectives include: 1) development of plant germplasm that is both non-toxic and persistent, which could involve germplasm infected with novel endophytes or germplasm that is endophyte-free; 2) development of management practices that improve animal performance and reduce effects of heat stress associated with fescue toxicosis in animals; 3) further evaluation of fescue toxicosis effects on animal physiology and recovery from this condition; and 4) identification of markers of animal sensitivity to heat stress and fescue toxicosis.

1b. Approach (from AD-416):
Tall fescue, infected with endophytes that do not produce animal toxic alkaloids, will be tested for animal toxicosis in feeding and grazing trials. Persistence of new germplasms will be measured in grazed pastures. Forage management practices will be developed to control and reduce toxicity of tall fescue. Endophyte-free germplasm with increased concentrations of plant proteins associated with nematode resistance will be tested for persistence. New approaches to monitor body temperature will be established and used to evaluate techniques for reducing heat stress. Treatments that promote healthy immune systems, like antioxidant activity and body temperature regulation, will be assessed for effects on severity of fescue toxicosis under field and in climate-controlled environmental chambers. Genetic and physiological markers of animal sensitivity to heat stress and fescue toxicosis will be identified to improve selection of animals that are more resistant to these problems.

3. Progress Report:
Problems associated with animal intake of tall fescue (Lolium arundinaceum) infected with the endophyte Neotyphodium coenophialum are well known. The primary ones include reductions in feed intake and weight gain. Also, internal body temperature increases above normal level during the summer months. The following report is a summary of multidisciplinary studies over 5 years in both animal and plant sciences to address these problems. From the animal side there is little knowledge of long-term responses to fescue toxicosis and heat stress. Cattle were tested in both field and chamber environments to identify the components of physiological adaptation to these stressors. Despite evidence of thermoregulatory adjustment to these stressors, some thermal responses characteristic of fescue toxicosis (i.e., skin temperature) still show increased sensitivity to a change in air temperature. Depressed feed intake and sweat rate in response to fescue toxicosis and heat stress did not exhibit adaptation. Cattle with fescue toxicosis continued to exhibit a lower extremity skin temperature with a drop in air temperature to suggest reduced blood flow under these conditions. These markers might be used to identify animal sensitivity to these environmental stressors. Cattle raised for generations on endophyte-infected tall fescue may have an acquired tolerance to fescue toxicosis, and this was tested using animals breed from different US regions where tall fescue is present (Missouri) or absent (Oklahoma). Although both groups exhibited a reduction in feed intake on an infected fescue diet, the Oklahoma animals exhibited a greater reduction in skin temperature at cool temperatures to support the previous finding. Throughout all of these studies, tests have been performed to determine animal sensitivity to fescue toxicosis. Adaptation to heat stress reduces this sensitivity, with animal sensitivity to fescue toxicosis changing over time even in nonheat stress environments. Little is known about changes in ruminal temperature after consumption of endopyte-infected tall fescue. Consumption of endophyte-infected tall fescue seed by steers caused a considerable increase in rectal temperature. Unexpectedly, ruminal temperature showed only a minimal increase which is likely due to a decline in feed intake and an associated reduction in heat production. Research has shown that fescue toxicosis can impact immune function. Studies were conducted using rats to assess the combined impact of heat stress and ergopeptine alkaloids on the immune system. A combination of alkaloid intake and heat stress significantly affected the proportion of circulating natural killer and immune B cells, with more modest changes in immune T cells. Our studies also have shown the effect of endophyte-infected tall fescue intake on hepatic gene expression in rats. This work identifies the liver as a major participant in the pathology of fescue toxicosis, as it is the site where toxins are metabolized in the body. As a result of fescue toxicosis, gene expressions for cytochrome P450 are up-regulated and expressions of antioxidant enzymes are down-regulated. Various heat shock proteins associated with heat stress resistance, such as small stress protein and serine protease, are also down-regulated. Similar studies of cattle identied 76 genes whose expression was significantly altered in response to the consumption of endophyte-infected tall fescue, including genes involved in B oxidation, oxidative phosphorylation, Phase II conjugation reactions, and antioxidant activity. Studies using both rat and cattle have shown that the reduced feed intake and hyperthermia associated with fescue toxicosis are separate, independent responses. The decreased feed intake is the more sensitive response appearing under both neutral and heat stress conditions, even in the absence of hyperthermia. Over the last 2 years we have shifted focus to include the development of avenues that can be used to communicate more effectively with producers. To accomplish this, we have worked with a USDA fellow and leveraged funding from the University to develop a smartphone application that allows producers to identify heat stress in their livestock. Since the effect of fescue toxicosis is compounded by heat stress, this decision-making tool will ultimately improve the welfare and productivity of cattle grazing endophyte-infected pastures. The application is titled ThermalAid and can be found at: It is currently only available for iPhone use, with the android version currently in development. In addition to the smartphone application, we have developed a companion website called ThermalNet that provides the producer with more detailed information on reducing the impact of both heat stress and fescue toxicosis. The ThermalNet site can be found at: It is extremely important that products from many years of research be made available to users. This is the outcome of the funds provided for this project. The plant science group has also directed their attention toward discoveries that directly benefit the animal and producer. Their work has gone into a number of different areas that are all related to fescue toxicosis and reducing the problems associated with this condition. One study showed that endophyte status has no effect on cold tolerance of fescue, which seems to be controlled by the genotype. Another multi-year study found that systems with bermudagrass result in much higher steer gains until early September; during the fall months, steers without bermudagrass "catch up" to those coming from bermudagrass to toxic tall fescue. A study was performed to determine the fate of ergot alkaloids with varying canopy height of fescue plants. Effects of drought on endophyte-free and infected tall fescue was examined and expression of stress proteins (i.e., dehydrin and superoxide dismutase, or SOD) and membrane stability (less leakage) was found to be greater for the natural, nontoxic endophyte than the endophyte-free type. Higher antioxidant activity afforded by endophyte stimulation of SOD activity may be a key mechanism by which plasma membranes are protected against lipid peroxidation, and can thus retain viability until water supply becomes favorable. Collaborative research (Arkansas/Missouri) has led to development of a new tall fescue containing a "friendly" fungus. This fungus makes the plant more resistant to drought and disease, but it is not toxic to cattle. Steers gain weight twice as quickly on the new fescue compared to endophyte-infected Kentucky-31. Additionally, improved forage management systems now in place have helped more than 24,000 producers lessen the impact of endophtye-infected tall fescue. Animal-oriented achievements include development of feeding management techniques that reduce heat stress due to fescue toxicosis, testing of new feed additives, and development of monitoring techniques for animal health. Products from this research project have saved Missouri's beef producers more than $1.4 billion over the past 10 years. Nationwide, improvements would include management to reduce toxin production and ingestion. If only 10% of the US livestock adopted these practices, the income would increase by a total of $90 million each year.

4. Accomplishments

Last Modified: 10/19/2017
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