Location: Forage-animal Production Research2012 Annual Report
1a. Objectives (from AD-416):
The long-term goal of this project is to improve competitiveness and sustainability of forage-based animal enterprises in the transition zone between the subtropical south and temperate north of the eastern half of the United States. Over the next 5 years the Forage-Animal Production Research Unit (FAPRU) and collaborators will focus on the following objectives: Objective 1: Improve forage-animal health, performance, and forage intake and utilization. Subobjective 1.A. Develop and validate analytical methodologies for profiling ergot alkaloids produced by toxic endophyte-infected (TE) tall fescue (TF), and resulting metabolites following consumption and metabolism by animals. Subobjective 1.B. Identify the biotic components and mechanisms of the animal-plant interface impacting grazing animal health and production. Subobjective 1.C. Enhance nutrient utilization through an improved understanding and manipulation of microorganisms of the rumen. Objective 2: Improve animal and forage productivity of forage-based systems through optimization of grazing and preconditioning management protocols. Subobjective 2.A. Evaluate animal performance on novel endophyte-infected TF pastures. Subobjective 2.B. Develop a preconditioning program to reduce morbidity and mortality in feeder calves that have been backgrounded on TE TF.
1b. Approach (from AD-416):
Forage systems provide low-cost feed, conserve soil and water resources, and mitigate man’s impact on the environment. However, basic biological information is limited on how plant metabolites affect animal performance and health beyond the production level. Fundamental information concerning how these production level effects are elicited has only recently become a focus. As such, the available information for predicting animal performance in response to plant nutrients under varying environmental, genetic, physiological status, and management conditions is of limited use. Even more problematic is the poor understanding of the effects of plant nutraceuticals and anti-quality factors on nutrient intake, metabolism and assimilation for product, health maintenance, or work by the animal. To increase the sustainability of forage-based enterprises, it is essential that a better understanding be developed of the fundamental biological processes underlying the interactions between the animal, plant, and environment. This project, through the development and utilization of cutting-edge technologies and real world testing, proposes to decipher the complex interactions within the animal-plant interface in order to accomplish the following two objectives: 1) improve forage-animal health, performance, and forage intake and utilization; and 2) improve animal and forage productivity of forage-based systems through optimization of grazing and preconditioning management protocols. These objectives will be focused on the predominant forage (tall fescue) of the transition zone and its alternatives. Accomplishing these objectives will improve sustainability of forage-based enterprises through more reliable predictions on the impacts of management and environment on animal health and performance.
3. Progress Report:
Project scientists made progress in improving (enhancing sensitivity from low picomoles to femtomoles on column) our ability to detect tall fescue alkaloids (and related alkaloids from ergot) in animal tissues and fluids, including running of some preliminary real world samples. Project scientists are currently working on finalizing validation data on several matrices for publication. Following this, tissues collected from alkaloid exposed animals will be analyzed to determine alkaloid distribution and potential food safety issues. Further, project scientists completed a two year study following the effects of steer withdrawal from ergot alkaloid endophyte infected tall fescue. They demonstrated with this study that alkaloid induced vasoconstriction mediated via serotonergic receptor 2A and alpha-adrenergic receptors 2A and 2C did not return toward normal function until animals had been off the forage for more than a month. Project scientists validated COX IV and glucocorticoid receptor antibodies for use in study of ergot alkaloid induced changes in liver tissue. Using the antibodies, they demonstrated that cytochrome C oxidase (COX IV) was elevated in liver tissue of steers exhibiting fescue toxicosis. Using the fescue toxicosis model developed and validated over the past few years, project scientists have started the initial studies of ergot alkaloid effects on nutrient metabolism and absorption. In addition, these scientists develop and evaluated techniques to measure fasting heat production in alkaloid intoxicated animals. Project scientists using Doppler ultrasonography demonstrated that ergot alkaloid containing tall fescue seed could induce vasoconstriction of the palmar and uterine artery in the horse, identifying vasoconstriction as a mechanism in horse fescue toxicosis. Further, project scientists have identified two markers of bone turnover for study of ergot alkaloid effects on horse growth and development. Project scientist conducted a grazing experiment and have shown that suppressing seed head production by toxic endophyte-infected tall fescue results in improved steer performance on pasture.
1. Chemical suppression of seedhead emergence to mitigate fescue toxicosis. Tall fescue is a cool-season perennial grass extensively utilized for grazing and hay production on approximately 15 million hectares. A fungal endophyte infects tall fescue plants and produces ergot alkaloids that cause fescue toxicosis. Cattle selectively graze tall fescue seedheads, which can be problematic because ergot alkaloid concentrations in seedheads are greater than in leaf blades and sheaths. Chaparral® herbicide, applied early in vegetative growth, can suppress seedhead emergence in tall fescue to potentially mitigate fescue toxicosis and enhance calf weight gain. However, pasture carrying capacities could be substantially reduced compared to tall fescue without chemical suppression of seed heads. An experiment was conducted that evaluted steer and pasture responses to seed head suppression with light and moderate grazing intensities. Results showed reduced carrying capacities with seed head suppression, but higher steer weight gains with the treatment compensated for the lower capacities in generating weight gains per acre that were similar to those of untreated pastures. This management approach provides a way to improve the efficiency of backgrounding beef calves on toxic endophyte-infected tall fescue for feedyard finishing.
2. Ergopeptines inhibit a specific, ubiquitously-expressed, nucleoside transporter (ENT1). Neotyphodium coenophialum-infected tall fescue contains ergopeptines. Except for interactions with biogenic amine receptors (e.g., dopamine type-2 receptor, DR2), little is known about how ergopeptines affect animal metabolism. The effect(s) of ergopeptines on bovine nucleoside transporters (NT) was evaluated using Madin-Darby Bovine Kidney (MDBK) cells. Equilibrative NT1 (ENT1)-like activity accounted for 94% of total NT activity. Inhibitory competition (IC50) experiments found that this activity was inhibited by both bromocriptine (a synthetic model ergopeptine and D2R agonist) and ergovaline (a predominant ergopeptine of tall fescue). Kinetic inhibition analysis indicated that bromocriptine inhibited ENT1-like activity through a competitive and non-competitive mechanism. Domperidone (a D2R antagonist) inhibited ENT1 activity more in the presence than absence of bromocriptine, and displayed an IC50 value lower than bromocriptine or ergovaline, suggesting that inhibition was not through D2R-mediated events. These novel mechanistic findings imply that cattle consuming endophyte-infected tall fescue have reduced ENT1 activity, thus body-wide impaired nucleoside (nitrogen containing compound) metabolism and physiological functions.
Goff, B.M., Aiken, G.E., Witt, W.W., Sleugh, B.B., Burch, P. 2012. Steer consumption and ergovaline recovery from in vitro digested residues of tall fescue seedheads. Crop Science. 52:1437-1440.