|GOFF, B - University Of Kentucky|
|WITT, W - University Of Kentucky|
|SLEUGH, B - Dow Agrosciences|
|BURCH, P - Dow Agrosciences|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2011
Publication Date: 5/1/2012
Citation: 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.
Interpretive Summary: Tall fescue toxicosis is a common condition among cattle and other animals grazing tall fescue pastures within the transition zone of the United States between the temperate northeast and the subtropical southeast. This common forage grass is known to have a mutualistic relationship with a fungal endophyte that results in the production of ergot alkaloids. Ergot alkaloids are believed to be responsible for the common symptoms of fescue toxicosis, such as elevated body temperatures, rough hair coat, and poor weight gain. Among the various types of ergot alkaloids produced by the fungal endophyte, ergovaline, has been implicated as being the most potent in affecting animal physiology. Ergovaline concentrations can be three times greater in seedheads than in leaf tissue, making the reproductive growth of the grass a management concern because cattle selectively graze fescue seed heads. An experiment was conducted to quantify the degree to which cattle consumed tall fescue seedheads during grazing and to determine the amount of ergovaline that could be potentially released from seeds during digestion. Findings from this study indicate that Steers grazed off approximately 80 % of the seedheads during the early summer months when seed heads contained their highest ergovaline concentrations. Release of ergovaline from seed tissues during in vitro digestion was nearly 100%. Results indicated that consumed seed heads are a major source of ergovaline in cattle. Management to control the emergence of fescue seed head could have major implications in improving the weight gain and well being of cattle grazed on endophyte-infected pastures.
Technical Abstract: Ergot alkaloids produced by the endophyte [Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin] of tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] are a common problem faced by cattle producers. These toxins are concentrated within seedheads of tall fescue tillers, which cattle were observed to selectively graze. There appears to be little research showing the extent that alkaloids are released from developing seedheads during digestion. Therefore, the objectives of this study were to determine the extent at which tall fescue seedheads were removed by cattle during the growing season and to estimate the amount of ergovaline that is potentially released from these tissues into the rumen. Reproductive tillers were collected from endophyte-infected tall fescue pastures during the summer of 2010. The amount of seedheads that were grazed by steers was also monitored at this time. Seeds were digested with a two-stage acid-pepsin procedure and ergovaline concentrations were determined using an HPLC method. By 4 June, 60.7 ± 2.87% of seedheads within the pastures had been grazed, and increased to nearly 80 ± 0.82% two weeks later. Ergovaline concentrations of seedheads increased throughout the season and were highest in mid-June. The percentage of ergovaline released from seedheads collected in mid-June was reduced compared to other dates, but the difference was small. The results of this study indicate that ergovaline concentrations of tall fescue seedheads may contribute greatly to the symptoms of tall fescue toxicosis, and management strategies should be aimed at controlling reproductive growth of the grass.