2008 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.
Results from the Romosinuano-Angus studies were further analyzed for blood differences before and during a 2-week heat exposure. Plans are now in place with ARS-Florida to bring additional Romosinuano cattle to Missouri, beginning fall 2008, for testing in 2009. These heat-tolerant cattle will be tested along with heat-sensitive Angus cattle of similar age and size from Missouri in the Brody Environmental at the University of Missouri. They will be initially tested to determine heat stress response, followed by feeding endophyte-infected diets under the same heat conditions.
A study began spring 2008 to evaluate long-term responses of cattle to fescue toxicosis. Cattle were placed on endophyte-infected or uninfected pastures in June. After more than a month on pasture, they were brought into environmental chambers for testing under the same conditions during controlled heat stress. These tests will identify responses during peak summer heat. They will be returned to pasture and retested under the same heat stress and diet conditions after they have recovered from the summer heat. All animals will have telemetric temperature transmitters for continuous monitoring of core temperature in field and laboratory environments. In additions to normal physiological measurements in the chambers, animals will have tissue and blood samples taken for biochemical analyses and Real-Time PCR.
Cattle exposed to heat stress have reduced feed intake, lower growth and conception rates, panting activity, increased peripheral blood flow, and sweating. Although these effects are well documented, the changes in cellular function and gene regulation are poorly understood. Liver is one of the major organs involved in the regulation of metabolism and heat production. The goal of this study is to investigate the changes in gene regulation in liver of cattle under long-term mild heat stress.
Many of the ongoing field studies are near completion. Samples have been collected, dried and ground, and they are currently being analyzed for ergovaline and total ergot alkaloids. These samples are from studies that determine alkaloid production as influenced by poultry litter, commercial fertilizers, herbicides, as well as concentrations that change throughout the calendar year and during haymaking. Additional samples will be collected and analyzed during 2008; these additional samples determine the influence of silage moisture on alkaloid concentration.
Experiments on minimizing ingestion of ergot alkaloids in tall fescue-based grazing systems are midway to completion. These studies focus on using Bermuda grass, instead of endophyte-infected tall fescue, in early summer to minimize ingestion of ergot alkaloids by stocker cattle. These are long-term, whole-forage systems experiments. Forage samples and animal performance data for 2007 are being analyzed; data for 2008 is still being collected.
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 College Station, TX (Jan. 2008) and Joplin, MO (Feb. 2008).
Tall fescue toxicosis appears to be made worse by high ambient temperatures:
Researchers at the University of Missouri evaluated heat tolerance of two Bos taurus breeds (Romosinuano, a tropically adapted breed, and Angus) with known differences in heat tolerance. Romosinuano cattle were more tolerant to heat stress than Angus cattle. Serum leptin, a hormone produced from fat cells, increased for both breeds during heat stress. A study conducted this year has identified physiological and endocrine markers that may aide in the identification of Bos taurus breeds that will have increased performance while grazing toxic fescue during hot weather. (Components 1 and 2 of NP 101)
Toxic tall fescue consumed by cows may result in decreased calf performance:
Researchers at the University of Missouri determined the effects of endophyte infection level of stockpiled tall fescue on the performance of lactating, fall-calving beef cows and their calves. Ergot-like alkaloids in toxic tall fescue decreased by approximately 50% from December through February; however, weight loss and body condition of lactating beef cows was still influenced by endophyte infection level. Nursing calves did not show changes in ADG or weaning weight based on the endophyte infection level. These data suggest that fall-calving herds can utilize highly infected tall fescue when stockpiled for winter grazing, with minimal impact on cow performance and no impact on calf gain. (Component 2 of NP 215).
|Number of Non-Peer Reviewed Presentations and Proceedings||4|