title: Evaluation of a ruminally dosed tall fescue seed extract as a model for fescue toxicosis in steers.
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 DMI 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 2-period crossover experiments to determine the effectiveness of ruminal dosing of a tall fescue seed extract to induce fescue toxicosis. This experiment used 4 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+; 4.1 mg/kg of ergovaline) and uninfected (E-; 0.0 mg/kg of ergovaline) KY-31 tall fescue seed was ground and dosed or extracted with ethanol, concentrated, and lyophilized before ruminal dosing. Ergovaline concentration of the final extract was 102 mg/kg. Animals were given a minimum of a 3-wk washout period between treatments. Physiological indicators were measured over 7 d at 22°C (d 1 to 3) and 32°C (d 4 to 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 < 0.001), and increased respiration rate (P < 0.01) and core temperature (P < 0.05) during both seed and extract dosing. Increasing environmental temperature from 22 to 32°C reduced total intake (P < 0.05) and increased core temperature (P < 0.001) and respiration rate (P < 0.001) during both seed and extract dosing. Diastolic blood pressure tended (P < 0.09) to be increased 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.
authors: Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546, USA.
authors: A F
authors: AF
authors: Koontz
authors: L P
authors: LP
authors: Bush
authors: J L
authors: JL
authors: Klotz
authors: K R
authors: KR
authors: McLeod
authors: F N
authors: FN
authors: Schrick
authors: D L
authors: DL
authors: Harmon
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000139:chemically induced*; D004879:Ergotamines / Q000737:chemistry / Q000633:toxicity; D008129:Lolium / Q000737:chemistry*; D008297:Male; D010936:Plant Extracts / Q000008:administration & dosage / Q000737:chemistry / Q000633:toxicity*; D010947:Plants, Toxic / Q000633:toxicity*; D012417:Rumen; D012639:Seeds / Q000737:chemistry / Q000633:toxicity*
chemical_list: D004879:Ergotamines; D010936:Plant Extracts; C076760:ergovaline