Location: Forage-animal Production ResearchTitle: Changes in bovine vascular contraction and constriction relative to time off endophyte-infected tall fescue Author
Submitted to: Joint Meeting of the ADSA, AMSA, ASAS and PSA
Publication Type: Abstract Only
Publication Acceptance Date: 3/6/2012
Publication Date: 7/15/2012
Citation: Bussard, J.R., Aiken, G.E., Strickland, J.R., Brown, K.R., Goff, B.M., Foote, A.P., Klotz, J.L. 2012. Changes in bovine vascular contraction and constriction relative to time off endophyte-infected tall fescue. J. Anim. Sci. Vol. 90, Suppl. 3:34. Interpretive Summary:
Technical Abstract: Beef cattle grazing endophyte-infected (E+; Neotyphodium coenophialum) tall fescue (TF; Lolium arundinaceum) are exposed to ergot alkaloids when consuming forage. Ergot alkaloids induce constriction in vascular tissue of extremities of animals grazing TF leading to inability to regulate body temperature and an increased susceptibility to heat and cold stresses. To better understand consequences of alkaloid exposure, a study was conducted to evaluate changes in vascular contraction relative to time-off E+ TF pasture after an 88-d grazing period. Lateral saphenous veins were biopsied from 24 predominantly Angus steers (361±4 kg) at 0-, 21-, 42-, and 63-d off of TF pasture (n=6 per time point) and 6 steers (370±18 kg) off of bermudagrass (BG) pasture on d-0 and d-63 (n=3 per time point). Off pasture, steers were housed in a dry lot and fed a non-toxic corn silage diet. To evaluate contractile response, biopsied vessels were cleaned, incubated in a multimyograph, and exposed to increasing concentrations (1x10-11 to 10-4 M) of ergotamine. Myograph data were normalized to a reference edition of 1x10-4 M norepinephrine. Cross-sectional ultrasound scans of caudal artery at the fourth coccygeal vertebra were taken on 0-, 8-, 15-, 21-, 29-, 36-, 42-, and 45-d using an Aloka 3500 Ultrasound Unit with a UST-5542 (13 MHz) linear array transducer set to 2-cm depth to determine mean artery luminal area to evaluate constriction. Data were analyzed as a CRD using mixed models in SAS with steer as experimental unit. Veins from steers of TF pasture differed over time (P<0.05) and d-0 TF veins had a much lower (P<0.05) contractile response to ergotamine compared to d-0 BG veins. By 63-d contractile responses of TF steers were similar to those of BG steers (P=0.29). Luminal areas of caudal arteries in steers grazed on E+ TF had relaxed and were similar to steers that had grazed BG by 36-d on non-toxic diet (P=0.15). Measures of contraction indicate that cattle should be removed from E+ TF pastures for greater than 4 weeks to obtain vascular responses similar to those of cattle grazed on BG pastures.