Location: Forage-animal Production ResearchTitle: Vasoactivity and vasoconstriction changes in cattle related to time off toxic endophyte-infected tall fescue
|BUSSARD, JESSICA - University Of Kentucky|
|FOOTE, ANDREW - University Of Kentucky|
|HARMON, DAVID - University Of Kentucky|
|GOFF, BEN - University Of Kentucky|
|SCHRICK, F. NEAL - University Of Kentucky|
|STRICKLAND, JAMES - Clemson University|
Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2016
Publication Date: 9/22/2016
Citation: Klotz, J.L., Aiken, G.E., Bussard, J.R., Foote, A.P., Harmon, D.L., Goff, B.M., Schrick, F., Strickland, J.R. 2016. Vasoactivity and vasoconstriction changes in cattle related to time off toxic endophyte-infected tall fescue. Toxins. 8:271. doi:10.3390/toxins8100271.
Interpretive Summary: This series of studies evaluated the vascular recovery of cattle following their removal toxic endophyte-infected tall fescue pastures. Knowledge of how cattle recover after grazing fungally-infected pastures is important to producers when making decisions related to animal performance or the sale and transport of those cattle. Through the use of in vivo and in vitro technologies, it was determined that a complete vascular recovery did not occur before 5 weeks on a non-toxic diet. These findings indicated that during this recovery period cattle may be more susceptible to external stressors (such as heat stress) and less able to adapt to changes in their environment. This is a much longer period of recovery time than previously thought, when compared to other measures of recovery from fescue toxicosis, such as core body temperature or serum prolactin.
Technical Abstract: Previous research has indicated that serotonergic and a-adrenergic receptors in peripheral vasculature are affected by exposure of cattle grazing toxic endophyte-infected (E+; Epichlöe coenophialia) tall fescue (Lolium arundinaceum). The objective of this experiment was to determine the period of time necessary for the vascular effects of ergot alkaloids to subside. Two experiments were conducted to investigate changes in vascular contractile response and vasoconstriction over time relative to removal from an ergot alkaloid-containing E+ tall fescue pasture. In Experiment 1 lateral saphenous vein biopsies were conducted on 21 predominantly Angus steers (357 ±3 kg body weight) at 0- (n = 6), 7- (n = 6), 14- (n = 5), or 28-days (n = 4) after removal from grazing pasture (3.0 ha) for 126 days. In Experiment 2 lateral saphenous veins were biopsied from 24 Angus-cross steers (361 ±4 kg body weight) at 0-, 21-, 42-, and 63-days off of tall fescue pasture (n = 6 per time point) and 6 steers (370 ±18 kg body weight) off of bermudagrass pasture on day-0 and day-63 (n = 3 per time point). Additionally, in Experiment 2 cross-sectional ultrasound scans of caudal artery at the fourth coccygeal vertebra were taken on 0-, 8-, 15-, 21-, 29-, 36-, 42-, and 45-days to determine mean artery luminal area to evaluate vasoconstriction. In both experiments, steers were removed from pasture and housed in a dry lot and fed a corn silage diet for the duration of biopsies and ultrasound scans. Biopsied vessels used to evaluate vasoactivity were cleaned, incubated in a multimyograph, and exposed to increasing concentrations of 4-Bromo-3,6-dimethoxybenzocyclobuten-1-yl) methylamine hydrobromide (TCB2; 5HT2A agonist), guanfacine (GF; a2A-adrenergic agonist), and (R)-(+)-m-nitrobiphenyline oxalate (NBP; a2C-adrenergic agonist) in both experiments and ergovaline (ERV) and ergotamine (ERT) in Exp.1 and Exp. 2, respectively. In Experiment 1, days off pasture × agonist concentration was not significant (P > 0.1) for all 4 compounds tested. In Experiment 2, GF, NBP, TCB2 and ERT were significant for days off pasture × agonist concentration interaction (P < 0.02) and vasoactivity increased over time. Vasoactivity to agonists was reduced (P < 0.05) when steers were initially removed from E+ tall fescue pasture compared to bermudagrass, but did not differ by d 63 for any variable. Luminal areas of caudal arteries in steers grazed on E+ tall fescue relaxed and were similar to steers that had grazed bermudagrass by 36-days on non-toxic diet (P = 0.15). These data demonstrate changes in peripheral vasoactivity and recovery from vasoconstriction occur beyond 5 weeks off toxic pasture and 5HT2A receptors appear to be more dramatically affected in the lateral saphenous vein by grazing E+ tall fescue pasture than adrenergic receptors.