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United States Department of Agriculture

Agricultural Research Service

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Location: Dale Bumpers Small Farms Research Center

2010 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
1) Response to heat stress may differ in Bos taurus originating in different US regions. Hourly measurements at specific heat stress levels may enable further understanding of these regional differences. Angus steers from Oklahoma (OK; n=6) and Missouri (MO; n=6) were compared to heat-tolerant Romosinuano steers (RO; n=5) from Florida in the University of Missouri Brody Environmental Center. Initially, the three groups were exposed to air temperature (Ta) treatments that included a constant thermoneutral temperature (TN) of 20 deg C for 8 days, followed by a daily heat cycle (HS1) of 28 to 38 deg C for 8 days, and a greater heat cycle (HS2) of 30 to 40 deg C for 8 days. Twenty-four hour measurements were made after stabilization at each temperature. Hourly measurements included rectal temperature (Tr), respiration rate (RR), and skin temperatures averaged at trunk and peripheral sites. There was no difference in Tr between groups at TN, but Tr was lower in RO compared to Angus during HS1 and HS2. Relationships between Tr and Ta were similar for MO and OK during HS1 and HS2. However, there was no relationship between Tr and Ta for RO during HS1 and HS2. RO had lower RR during TN and HS1, but were not different from Angus during HS2 to suggest an adaptive response. Interestingly, relationships between RR and Ta for RO were equal to Angus during HS1 and HS2, indicating no group difference in the RR relationship. Skin temperatures at trunk or peripheral sites were affected by hour of day during all three temperature treatments. There was also an hour x group effect on trunk temperature during all three periods, with no effect on peripheral sites. Geographic origin of Angus did not affect the heat stress response. Romosinuano steers exhibited characteristic heat tolerance, but showed that some temporal response to heat stress may differ in Bos taurus cattle originating in different US regions in response to prolonged heat exposure. 2) A study has been completed to determine the fate of ergot alkaloids with varying canopy height of fescue plants. This study was completed last fall and this spring in collaboration with USDA-ARS at Booneville, AR, and at two locations in Missouri, Mt. Vernon and Linneus. Further, 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 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. In FY 2010, 13 peer-reviewed journal articles, 15 abstracts, 5 invited presentations, and one monograph chapter resulted from this project. ADODR monitoring of this project was accomplished by frequent emails, telephone calls, and on-site visits between ADODR and University of Missouri scientists. Meetings between ADODR and SCA partners were held in Joplin, MO (February, 2010).

4. Accomplishments

Last Modified: 06/21/2017
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