Steer and Plant Responses to Chemical Suppression of Seedhead Emergence in Toxic Endophyte‐Infected Tall Fescue

Bussard

et al. 2016

Toxins

Previous research has indicated that serotonergic and α-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; endpoint ergovaline + ergovalinine = 1.35 mg/kg DM) 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 (n = 6 per time point) following removal from grazing tall fescue pastures (3.0 ha; first 88 days endpoint ergovaline + ergovalinine = 0.15 mg/kg DM; last 18 days endpoint ergovaline + ergovalinine = 0.57 mg/kg DM) for 106 total days. Six steers (370 ± 18 kg body weight) off of bermudagrass pasture for the same time interval were also biopsied 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 Days 0, 8, 15, 21, 29, 36, 42, and 45 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; α2A-adrenergic agonist), and (R)-(+)-m-nitrobiphenyline oxalate (NBP; α2C-adrenergic agonist) in both experiments and ergovaline (ERV) and ergotamine (ERT) in Experiments 1 and 2, respectively. In Experiment 1, days off pasture × agonist concentration was not significant (p > 0.1) for all four 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 Day 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 for 36 days on non-toxic diet (p = 0.15). These data demonstrate changes in peripheral vasoactivity and recovery from vasoconstriction occur beyond five weeks off toxic pasture and 5HT2A receptors appear to be more dramatically affected in the lateral saphenous vein by...

Section: Discussionmentioning

confidence: 97%

“…Twenty-four predominantly Angus steers (357 ± 3 kg body weight) grazed E+ Kentucky 31 tall fescue pastures (3 ha) for 126 days during a separate grazing study [12]. The total ergovaline (ergovaline + ergovalinine) concentration of the tall fescue pastures just prior to removal of the steers was 1.35 mg/kg DM.…”

Section: Methodsmentioning

confidence: 99%

Vasoactivity and Vasoconstriction Changes in Cattle Related to Time off Toxic Endophyte-Infected Tall Fescue

Klotz

Bussard

et al. 2016

Toxins

“…Distinct visual symptoms of chlorosis following treatment with Chaparral occurred in this study, and the plants remained in this state for a period of approximately 2 weeks. Other reports of chlorosis have been made in other work with this herbicide (Aiken et al, 2012). If this inhibition of photosynthesis occurs when reserves are low, such as in the early spring, tall fescue plants may not have been able to maintain their metabolism during this period of stress, resulting in death of the plants.…”

Section: Application Rate and Date Effects On Seedhead And Plant Densmentioning

confidence: 68%

“…The lack of an impact from an early‐spring application on tall fescue seedhead suppression was somewhat surprising. In previous research, Chaparral (Aiken et al, 2012; Goff et al, 2012a) and other herbicides used to regulate reproductive growth in cool‐season grasses (Glenn et al, 1981; Roberts and Moore, 1990; Moyer and Kelley, 1995) were applied on similar dates (mid to late March) and stages of development (i.e., vegetative) with effective results. The reduced efficacy of the herbicide during this period in this study may be the result of warmer conditions during the winter and early‐spring months of the growing season.…”

Section: Application Rate and Date Effects On Seedhead And Plant Densmentioning

confidence: 99%

Timing and Rate of Chaparral Treatment Affects Tall Fescue Seedhead Development and Pasture Plant Densities

Goff¹,

Witt³

et al. 2014

Forage grazinglands

Self Cite

The herbicide, Chaparral, has been shown to suppress seedhead development in tall fescue (Lolium arundinaceum) pastures and reduce the symptoms of tall fescue toxicosis in cattle. However, little is known about the logistics of herbicide treatment on tall fescue pastures. The objective of this study was to determine the effect of three rates of Chaparral on tall fescue pasture when applied at three times (October, March, and April) during the growing season. Chaparral reduced seedhead densities of tall fescue on all treatment dates, but the highest levels of suppression were achieved with a late‐spring treatment, when tall fescue was in the early stages of reproductive growth. This treatment was also the least detrimental to tall fescue plant densities. Chaparral applied to vegetative tall fescue in the early spring had the least effect on seedhead densities but significantly reduced the density of tall fescue crowns. Other species of grass began to encroach into tall fescue stands following herbicide treatment during the fall and early spring. Delaying Chaparral until late spring may be more effective for producers because it may allow for greater control of seedheads with less loss in tall fescue and the potential for higher forage yields. There was some effect of suppressing reproductive growth of tall fescue with a fall treatment of Chaparral, but more research may be needed to evaluate its merit over a late‐spring treatment.

“…The active ingredient, Metsulfuron-methyl, does not suppress seed head emergence of Kentucky bluegrass (Poa Pratensis L.) or orchardgrass (Dactylis glomerata L.) Goff, 2012). Aiken et al (2012) reported that in lightly-grazed mixed cool-season grass pastures that were treated or not treated with metsulfuron for seedhead suppression, the incidence of seedheads were nearly 10-fold greater in untreated than treated pastures. Although seedhead emergence declined, forage mass also declined.…”

Section: Chapter I: Introductionmentioning

confidence: 99%

Animal and Pasture Responses to Grazing Management of Chemically Suppressed Tall Fescue in Mixed Pastures

Williamson

Flynn³

et al. 2016

Crop Science

Self Cite

Treatment of toxic endophyte‐infected tall fescue [Lolium arundinaceum (Schreb.) Darbysh] with metsulfuran‐methyl {Methyl 2‐[[[[(4‐methoxyl‐6‐methyl‐1,3,5‐triazin‐2‐yl)‐amino]carbonyl]amino]sulfonyl] benzoate}, as delivered by Chaparral herbicide (Dow AgroSciences, Indianapolis, IN) can mitigate fescue toxicosis and enhance forage nutritive value by suppressing seedhead emergence. A grazing experiment was conducted with steers (2013) and heifers (2014) to evaluate animal and plant responses to grazing management of mixed cool‐season grass pastures treated with Chaparral. Continuous and rotational stocking treatments were assigned to six, 3.0‐ha pastures in a randomized complete block design with three replications in 2013 and two replications in 2014. Each pasture had six tester animals, and stocking rates were varied using put‐and‐take animals. Pastures were grazed from 16 April to 8 July 2013 and 20 May to 12 Aug. 2014. Pasture carrying capacity was 20% greater for rotational than continuous stocking. Calves on rotationally stocked pastures also had 26% greater average daily gain (ADG) and body weight (BW) gain per hectare than those on the continuous treatment. Pre‐grazed herbage had less neutral detergent fiber (NDF) and acid detergent fiber (ADF) than post‐grazed herbage and herbage from continuously stocked pastures in 2013, but they did not differ in 2014. Crude protein (CP) was lower in post‐graze rotational pasture than in continuous or pre‐graze rotational pasture. Fescue roots in rotationally stocked pastures had greater water soluble carbohydrates (WSC) and N concentrations than continuously stocked pastures following the second year of grazing. Results indicated that rotational stocking of Chaparral treated mixed pastures can improve animal performance and pasture productivity.