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.
Bos taurus cattle from different regions of the US may differ in their response to heat stress. To compare the response to fescue toxicosis across breeds with different levels of heat tolerance, it is important to test then at levels of heat stress that produce comparable levels of heat strain. The physiological responses to heat stress of heat-sensitive Angus steers from Oklahoma (OK; n equal 12) and Missouri (MO; n equal 12) were compared to those of heat-tolerant Romosinuano steers from Florida (RO; n equal 11) in the Brody Environmental Center at The University of Missouri. These cattle also were used in a pasture environment exposed to summer heat stress. All animals are implanted with telemetric temperature transmitters for hourly determinations of intraruminal temperature. Respiration rate was recorded twice daily on selected days throughout the period. In September 2009, cattle will be moved into the Brody Environmental Center (BEC) for a study that focuses on the differences in responses to endophyte-infected fescue and heat stress. Throughout the study, core temperature, respiration rate, skin temperature, and rectal temperature will be measured to determine change on endophyte-infected and uninfected diets from the onset at thermoneutrality and into heat stress. We will also be collecting liver tissue in thermoneutral and heat stress conditions for markers that might give us some insight into differences between cattle with and without fescue toxicosis. A study was conducted over the last year to determine biochemical and physiological responses of Angus cattle to dehydration during heat stress. We know from earlier studies that fescue toxicosis results in a decrease in cutaneous evaporative water loss. Since water balance is important under stress conditions we decided to determine markers of dehydration in the heat. A study on the seasonal production of ergovaline and ergot alkaloids was completed. This study was conducted with the University of Georgia and Clemson University. The study included both non-clipped plots, which reveals the total accumulation of alkaloids in a season, as well as frequently clipped plots, which reveals alkaloid concentration in grazed pastures. Two additional studies have been completed to determine the fate of ergot alkaloids during hay and silage production. The hay study was completed late last year and will be published this year. The silage study is currently being analyzed statistically. The silage study was conducted in collaboration with USDA-ARS at Booneville, Arkansas, and at two locations in Missouri, Mt. Vernon and Linneus.