|Koontz, Anne -|
|Bush, Lowell -|
|Mcleod, Kyle -|
|Schrick, Frank -|
|Harmon, David -|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 28, 2011
Publication Date: March 1, 2012
Citation: Koontz, A.F., Bush, L.P., Klotz, J.L., Mcleod, K.R., Schrick, F.N., Harmon, D.L. 2012. Evaluation of a ruminally dosed tall fescue seed extract as a model for fescue toxicosis in steers. Journal of Animal Science. 90:914-921. Interpretive Summary: As endophyte toxins are concentrated in tall fescue seed, research examining the effects of endophyte infected tall fescue on animal performance often utilizes ground seed added to a basal diet to induce symptoms of toxicosis. Because one of the factors associated with fescue toxicosis is a reduction in feed intake, achieving a consistent and adequate intake of toxins can be a complication. A more precise method would be to dose the animals with an extract containing the alkaloids found in toxic fescue. However, little research has been done to determine the bioactivity of such extracts. The goals of these experiments were: 1) To develop a set of standard physiologic measurements to characterize the onset of fescue toxicosis and 2) To determine the ability of a tall fescue seed extract to cause the symptoms of fescue toxicosis in steers. Ruminally cannulated steers with implanted remote telemetry core body temperature loggers were dosed with either infected or uninfected ground seed or seed extract at thermoneutral and heat stress temperatures. Ruminal dosing of ground seed and seed extract were able to mimic the classic symptoms of fescue toxicosis in cattle. This model whereby seed or extract is directly dosed into the rumen eliminates the possibility of reduced alkaloid intake due to refusal of feed by the animal. This model may allow for more precise and repeatable dosing of alkaloids in future fescue research and may enhance the ability to study underlying mechanisms of fescue toxicosis.
Technical Abstract: Tall fescue (Lolium arundinaceum) toxicosis research is often complicated by a reduction in intake of infected forage or seed making treatment comparisons difficult. This study was conducted to develop a fescue toxicosis model that would allow for variations in DM intake without altering the quantity of alkaloids consumed over the course of the experiment. Ground tall fescue seed and a tall fescue seed extract were used in two, two-period crossover experiments to determine the effectiveness of ruminal dosing of a tall fescue seed extract to induce fescue toxicosis. This experiment utilized four growing Holstein steers (BW = 337 ± 24 kg) surgically fitted with ruminal cannulas. Steers were maintained on a diet of endophyte free fescue hay fed ad libitum throughout the experiment. Endophyte infected (E+; 5.3 ppm ergovaline) and uninfected (E-; 0.0 ppm ergovaline) KY-31 tall fescue seed was ground and dosed or extracted with ethanol, concentrated and lyophilized prior to ruminal dosing. Ergovaline concentration of the final extract was 102 ppm. Animals were given a minimum of a three week washout period between treatments. Physiological indicators were measured over 7d at 22°C (d1-3) and 32°C (d4-7) during both seed and extract dosing. Seed and extract E+ dosing reduced serum prolactin concentrations such that they were not different from zero (P < 0.10). Treatment with E+ reduced feed intake (P < 0.05) and heart rate (P < 0.0001), and increased respiration rate (P < 0.01) and core temperature (P < 0.05) during both seed and extract dosing. Increasing environmental temperature from 22°C to 32°C reduced total intake (P < 0.05) and increased core temperature (P < 0.0001) and respiration rate (P < 0.0001) during both seed and extract dosing. Diastolic blood pressure tended (P < 0.1) to be elevated during E+ extract dosing and reduced during heat stress. These physiological alterations are consistent with those reported for cattle grazing or consuming seed from endophyte infected tall fescue. These data indicate that a ruminally dosed ethanol extract of tall fescue seed is efficacious in inducing fescue toxicosis in cattle.