|HARLOW, BRITTANY - Oak Ridge Institute For Science And Education (ORISE)|
|GOODMAN, JACK - University Of Kentucky|
|LYNN, BERT - University Of Kentucky|
|JI, HUIHUA - University Of Kentucky|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2016
Publication Date: 3/3/2017
Citation: Harlow, B.M., Goodman, J.P., Lynn, B., Flythe, M.D., Ji, H., Aiken, G.E. 2017. Ruminal tryptophan-utilizing bacteria degrade ergovaline from tall fescue seed extract. Journal of Animal Science. 95:980-988.
Interpretive Summary: Ergot alkaloids produced by a fungal endophyte that infects most plants of ‘Kentucky 31’ tall fescue cause persistent constriction of blood flow that incapacitates the animal’s ability to thermoregulate their core body temperature, and can also cause a reduction in the secretion of the hormone, prolactin. Consequently, ruminants that graze toxic endophyte-infected tall fescue can exhibit poor reproduction and growth performance that can annually cost the forage-based livestock industry well over a billion dollars. Previous research had reported there is some degradation of ergot alkaloids in the rumen of grazing animals, but the microorganisms responsible for this degradation have not been identified. A research study was conducted to identify the microorganisms responsible for this degradation and their effectiveness in degrading ergot alkaloids. Following 48 hour incubation of rumen fluid with ergot alkaloid extract, hyper ammonia-producing bacteria degraded 54 to 75 percent of the ergot alkaloid, ergovaline, the predominant ergot alkaloid produced by the endophyte. These results indicated that it may be possible to establish thresholds for ergovaline in the diet, below which it will be degraded by rumen microorganisms; however, the end products of this degradation will need to be identified for determination of their toxic properties. This research will be useful in developing management strategies to alleviate or mitigate fescue toxicosis and enhance grazing livestock performance and well-being.
Technical Abstract: The objectives of this study were to evaluate degradation of ergovaline in a tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] seed extract by rumen microflora ex vivo and to identify specific bacteria capable of ergovaline degradation in vitro. Rumen cell suspensions were prepared by harvesting rumen fluid from fistulated wether goats (n = 3), straining, and differential centrifugation. Suspensions were dispensed into anaerobic tubes with added Trypticase with or without extract. Suspensions were incubated for 48 h at 39°C. Samples were collected at 0, 24, and 48 h for ergovaline analysis and enumeration of hyper-ammonia producing bacteria (HAB) and tryptophan-utilizing bacteria. Enumeration data were log transformed for statistical analysis. When suspensions were incubated with extract, 11 – 15% of ergovaline disappearance was observed over 48 h (P = 0.0194). After 24 h, suspensions with added extract had 10-fold less HAB than controls (P = 0.0377), but treatments were similar by 48 h (P = 1.0). However, after 24 h and 48 h, suspensions with extract had 10-fold more tryptophan-utilizing bacteria (P < 0.0001) that were later isolated and identified by their 16S RNA gene sequence as Clostridium sporogenes. The isolates and other known rumen pure cultures (Streptococcus bovis JB1, Megasphaera elsdenii B159, Selenemonas ruminatium HD4, Prevotella bryantii B14, Ruminococcus flavefaciens, Clostridium aminophilum F, Clostridium sporogenes MD1, Clostridium sticklandii SR) were evaluated for the ability to degrade ergovaline in vitro. Pure culture cell suspensions were incubated as described above and samples were taken at 0 and 48 h for ergovaline analysis. All HAB, including the isolates, tested degraded ergovaline (54 – 75%; P < 0.05). Prevotella bryantii B14 was also able to degrade ergovaline but to a lesser capacity (12%; P < 0.05), but all other bacteria tested did not degrade ergovaline. The results of this study indicate which rumen bacteria may play an important role in ergovaline degradation and that microbiological strategies for controlling their activity could have positive implications on fescue toxicosis.