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United States Department of Agriculture

Agricultural Research Service

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Location: Forage-animal Production Research

2013 Annual Report

1a. Objectives (from AD-416):
Experiment 1: A grazing experiment will determine the effects that steroidal implants and rough hair coats retained in the summer months have on weight gain and physiology of steers on toxic tall fescue pasture in the late spring and early summer. Experiment 2: A grazing experiment will evaluate performance and physiology of yearling steers grazing a novel endophyte infected tall fescue developed for the upper transition zone (KYFA9301 tall fescue inserted with the AR584 novel endophyte).

1b. Approach (from AD-416):
Experiment 1: A grazing experiment will be conducted with 60 steers that are assigned to six, 3.0-ha pastures of toxic tall fescue. Pastures will be assigned either with or without daily feeding of soybean hull pellets (2.3 kg/steer). Five steers will be implanted with a progesterone-estradiol ear implant and the other steers will not be implanted. Grazing and data collection will be conducted from late April until middle July for a two year duration. Average daily gain, rectal temperature, serum prolactin, and forage mass and ergovaline concentrations are response measures to be taken. Experiment 2: A grazing evaluation will be conducted with four TF entries: a TF genetic line (KAFA9301) with or without insertion of the AR584 NE, MaxQ (‘Jessup’ TF inserted with the AR584 endophyte), and ‘KY-31’ infected with the TE. The four TF entries were no-till planted in the fall of 2006 in 1-ha pastures. Entries were assigned to pastures in a completely randomized design with 3 replications. The grazing experiment will be conducted for a 3-year duration, with grazing being initiated each year in early April and terminated following 84 days of grazing. Average daily weight gain, rectal temperature, sweating rate, serum prolactin, pasture carrying capacity, forage mass and nutritive values are the response measures to be taken.

3. Progress Report:
A grazing experiment was conducted in the spring of 2013 as the initial year of a 2-year grazing experiment to compare productivity and sustainability for mixed pastures (endophyte-infected tall fescue, bluegrass, and orchardgrass) that is with or without treatment with a metsufuron containing herbicide to suppress tall fescue seed head emergence. Tall fescue, the predominant forage grass utilized in the southeastern United States of America, is infected by a fungal endophyte that produces toxic ergot alkaloids. These alkaloids cause fescue toxicosis in cattle that annually costs the United States beef industry approximately 1 billion dollars. Data collected in the grazing experiment has shown increased weight gains and a mitigation of fescue toxicosis for steers grazing seed head suppressed fescue and the effects were consistent for light and moderate grazing intensities. Previous research has demonstrated that controlling emergence of the highly toxic seed heads in fescue pastures can vastly improve animal performance and mitigate fescue toxicosis. However, seed head suppression can reduce fescue production. Rotational grazing might be needed for the management to be sustainable. This first year of the experiment indicated that rotational grazed pastures will hold more cattle and will maintain higher percentages of tall fescue. A second experiment is being conducted with 8 steers from this experiment, 8 steers that grazed endophyte-infected tall fescue with no suppression (toxic control), and 8 that grazed bermudagrass pasture (non-toxic control). These steers will be placed on non-toxic diets in pens and monitored to determine differences in vasculature blood flows, blood alkaloid concentrations, and prolactin concentrations. The overall objective is to determine if and at what rate that ergot alkaloids can clear from the vasculature of cattle after they are switched from endophyte-infected tall fescue to non-toxic diets.

4. Accomplishments

Last Modified: 06/22/2017
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