Alterations in serotonin receptor-induced contractility of bovine lateral saphenous vein in cattle grazing endophyte-infected tall fescue

Serotonin receptor-mediated vasorelaxation occurs primarily through 5-HT4 activation in bovine lateral saphenous vein

To better understand mechanisms of serotonin- (5-HT) mediated vasorelaxation, isolated lateral saphenous veins from cattle were assessed for vasoactivity using myography in response to increasing concentrations of 5-HT or selective 5-HT receptor agonists. Vessels were pre-contracted with 1 × 10-4 M phenylephrine and exposed to increasing concentrations of 5-HT or 5-HT receptor agonists that were selective for 5-HT1B, 5-HT2B, 5-HT4, and 5-HT7. Vasoactive response data were normalized as a percentage of the maximum contractile response induced by the phenylephrine pre-contraction. At 1 × 10-7 M 5-HT, a relaxation was observed with an 88.7% decrease (p < 0.01) from the phenylephrine maximum. At 1 × 10-4 M 5-HT, a contraction was observed with a 165% increase (p < 0.01) from the phenylephrine maximum. Increasing concentrations of agonists selective for 5-HT2B, 5-HT4, or 5-HT7 resulted in a 27%, 92%, or 44% (p < 0.01) decrease from the phenylephrine maximum, respectively. Of these 5-HT receptor agonists, the selective 5-HT4 receptor agonist resulted in the greatest potency (-log EC50) value (6.30) compared with 5-HT2B and 5-HT7 receptor agonists (4.21 and 4.66, respectively). To confirm the involvement of 5-HT4 in 5-HT-mediated vasorelaxation, blood vessels were exposed to either DMSO (solvent control) or a selective 5-HT4 antagonist (1 × 10-5 M) for 5-min prior to the phenylephrine pre-contraction and 5-HT additions. Antagonism of the 5-HT4 receptor attenuated the vasorelaxation caused by 5-HT. Approximately 94% of the vasorelaxation occurring in response to 5-HT could be accounted for through 5-HT4, providing strong evidence that 5-HT-mediated vasorelaxation occurs through 5-HT4 activation in bovine peripheral vasculature.

Ergot alkaloid consumption alters serotonin receptor-induced vasoactivity in ovine umbilical vasculature

Consumption of ergot alkaloids during the second half of gestation has been shown to decrease umbilical artery vasoactivity resulting in decreased birth weights. Negative vascular effects of ergot alkaloids are mediated predominantly through serotonergic and adrenergic receptors in other tissues. Vasoactivity of serotonin (5-HT) receptors 5-HT2A and 5-HT1B/1D in umbilical artery and vein from ewes receiving endophyte-infected seed (E + 1.77 mg ergovaline/hd/d) or a control total mixed ration (CON; 0 mg ergovaline/hd/d) tall fescue seed at d-110 and d-133 of gestation was evaluated. Gravid reproduction tracts were collected from ewes. Two-mm sections of umbilical artery and vein were exposed to increasing concentrations of a 5-HT1B/1D agonist and 5-HT2A agonist. The 5-HT1B/1D agonist did not stimulate a contractile response in artery or vein or either gestation time point. 5-HT2A agonist caused large responses in artery with greatest occurring at d-110 and decreasing in magnitude as days of gestation increased (p < 0.05). On d-110 and 133 of gestation, arteries from CON ewes had greater contractile response than arteries collected from E+ ewes (p < 0.05). Veins responded to increasing concentrations of the 5-HT2A agonist. Maximal d-110 vein response was greater than d-133 when exposed to 5-HT2A agonist (p < 0.05). Unlike the artery, veins from E+ ewes had greater d-133 contractile response than CON (p < 0.05). Vascular contractions of umbilical artery and vein are induced by 5-HT2A receptor activity and not 5-HT1B/1D. Umbilical artery 5-HT2A receptor activity was more sensitive to seed treatment and could be responsible for ergot alkaloid-induced intra-uterine growth restriction.

Duration of ergovaline exposure influences serotonin-mediated vasoactivity of bovine mesenteric vasculature

Ergovaline (ERV), produced in toxic endophyte-infected tall fescue, causes potent vasoconstriction of bovine peripheral and visceral vasculature. Ergovaline acts as both an agonist and an antagonist in bovine gut blood vessels through serotonin (5-HT) receptors and it appears that the type of action could be influenced by the extent of ERV exposure. Because it was unclear how the duration of ERV exposure influences 5-HT-mediated vasoactivity, experiments were designed to evaluate how simultaneous or prior ERV exposure influenced 5-HT-mediated vasoactivity of mesenteric artery (MA) and vein (MV) segments from Holstein steers (N = 10). Vessels were incubated in Krebs-Henseleit buffer containing 0, 0.01, or 0.1 μM ERV for 24 h prior to the 5-HT dose-response or exposed to fixed concentrations of 0, 0.01, or 0.1 μM ERV simultaneously during the 5-HT dose-response. Vessels were suspended in chambers of a multimyograph containing Krebs-Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were exposed to increasing concentrations of 5-HT (5 × 10-8 M to 1 × 10-4 M) every 15 min and contractile responses were normalized as a percentage of the maximum contractile response induced by 120 mM KCl reference addition. Two-way analysis of variance was used to separately analyze data for each vessel type and duration of exposure using the MIXED procedure of SAS. When 5-HT concentration increased from 5 × 10-8 to 1 × 10-6 M, simultaneous addition of 0.1 μM ERV increased (P < 0.01) the contractile response of MV compared with additions of 0 and 0.01 μM ERV. At 1 × 10-4 M 5-HT, the simultaneous presence of 0.01 and 0.1 μM ERV decreased (P < 0.01) the contractile response of both MA and MV compared with 0 μM ERV addition. As 5-HT concentrations increased, the contractile response increased (P < 0.01) in both MA and MV with no previous ERV exposure, but decreased in MA and MV with 24 h prior exposure to 0.01 and 0.1 μM ERV. These data demonstrate that the duration of ERV exposure influences 5-HT-mediated vasoconstriction and likely vasorelaxation in bovine mesenteric vasculature. If ERV and 5-HT exposure occur simultaneously, ERV can act as a partial agonist of 5-HT-mediated vasoconstriction. If 5-HT exposure occurs after blood vessels have had prior ERV exposure, it appears that 5-HT may induce vasorelaxation of blood vessels. More research is needed to identify cellular and molecular mechanisms involved with 5-HT-mediated vasoactivity.

Isoflavone Containing Legumes Mitigate Ergot Alkaloid-Induced Vasoconstriction in Goats (Capra hircus)

Ergot alkaloids produced by a fungal endophyte that infects tall fescue (Lolium arundinaceum; (E+ TF) can induce constriction of the vasculature in ruminants, resulting in “fescue toxicosis”. Legumes contain isoflavones that have been demonstrated to prevent and reverse E+ TF vasoconstriction. Several legumes are conventionally utilized in ruminant production, but can vary in both isoflavone concentration and composition. A feeding study was conducted to determine if isoflavone supplementation via red clover (Trifolium pratense), white clover (Trifolium repens), or soybean (Glycine max) meal can alleviate vasoconstriction when wether goats were challenged with E+ TF seed. The basal diet was chopped grass hay ad libitum. Carotid luminal areas were obtained pre- and post-ruminal infusions of E+ TF seed (15 µg kg BW−1 ergovaline + ergovalanine ± red clover, white clover, or soybean meal at 2.61 mg kg BW−1). When goats were challenged with E+ TF seed, the mean carotid luminal areas decreased by 56.1% (p < 0.01). All treatments were able to partially mitigate vasoconstriction, with red clover being the most effective (+39.8%), and white clover and soybean meal eliciting an intermediate response (+30%, p < 0.01). Results indicate that legumes can relax vasoconstriction in goats consuming ergot alkaloids, despite differences in isoflavone profile and concentrations.

Endophyte Infected Tall Fescue: Plant Symbiosis to Animal Toxicosis

Endophyte-infected fescue is a major cool season forage used for livestock production in the United States and through other areas of the world. A unique aspect of this forage resource is the symbiotic relationship with an endophytic fungus (Epichloë coenophiala) that has detrimental impact on herbivores due to toxic ergot alkaloids. Research over the past 50 years has unveiled details regarding this symbiotic relationship. This review focuses on the origin of tall fescue in the United States and the consequences of its wide-spread utilization as a livestock forage, along with the discovery and toxicodynamics of ergot alkaloids produced by E. coenophiala. The majority of past ergot alkaloid research has focused on observing phenotypic changes that occur in livestock affected by ergot alkaloids, but recent investigation of the metabolome, transcriptome, and proteome have shown that fescue toxicity-related illnesses are much more complex than previous research suggests.

Identification of Breed Differences in Known and New Fescue Toxicosis Associated Phenotypes in Charolais-and Hereford-Sired Crossbred Beef Cows

Simple Summary

The consumption of toxic fescue has caused significant losses in the U.S. beef industry. Widely accepted symptoms of toxic fescue exposure include the retention of a thick hair coat, tissue necrosis in the extremities, and reduced nutrient absorption. However, there is variability in the severity of these symptoms, both across and within breeds. The objective of this study was to characterize the effect of fescue toxicosis across Hereford- and Charolais-sired cows for known and new fescue stress-associated phenotypes. Results indicated that Hereford cows had a lessened ability to shed their winter coat and regulate body temperature along with lower serum mineral concentrations compared to Charolais cows when exposed to toxic fescue. Differences between and within sire breed in hair shedding were also observed, providing further evidence of genetic variation. This study provides evidence of variability in the fescue toxicosis that is potentially useful for genetic selection to reduce fescue stress and characterizes effects on pregnant cows which may impact calves in utero.

Abstract

Beef cattle phenotypes are affected by the consumption of toxic fescue. Toxic fescue’s impact is dependent on heat stress and breed composition, with genetic variability for robustness to toxin exposure believed to exist within and across breeds. The study objective was to characterize the effect of fescue toxicosis across breeds for known and novel heat and fescue stress-associated phenotypes. One-hundred crossbred fall-calving Charolais- and Hereford-sired cows of parities 1–3 were allocated to graze either toxic fescue (n = 50), non-toxic fescue (n = 25), or a rotation between toxic and non-toxic fescue (n = 25) for 156 days. Phenotypes impacted by breed (genetics) included hair coat score (p < 0.0001), hair reduction/shedding rate (p < 0.05), rectal temperature (RT) (p < 0.0001), vaginal temperature (p < 0.05), serum phosphorus concentration (p < 0.02) and respiration rate (RR) (p < 0.003). Cows on toxic fescue experienced reduced hair shedding efficacy (p < 0.0001), higher vaginal temperatures (p < 0.0001), increased systolic blood pressure (p < 0.04), increased RR (p < 0.0001) and reduced average daily gain (p < 0.0001), compared to cows grazing non-toxic fescue. Calves born from cows with higher RT during the last third of gestation had higher RT at weaning (p < 0.02), indicating potential physiological effects of in utero heat stress. The study indicates that beef cows exhibit variable responses to toxic fescue within and across breeds which may impact future calf phenotypes.

Vasoactive Effects of Acute Ergot Exposure in Sheep

Ergotism is a common and increasing problem in Saskatchewan’s livestock. Chronic exposure to low concentrations of ergot alkaloids is known to cause severe arterial vasoconstriction and gangrene through the activation of adrenergic and serotonergic receptors on vascular smooth muscles. The acute vascular effects of a single oral dose with high-level exposure to ergot alkaloids remain unknown and are examined in this study. This study had two main objectives; the first was to evaluate the role of α₁-adrenergic receptors in mediating the acute vasocontractile response after single-dose exposure in sheep. The second was to examine whether terazosin (TE) could abolish the vascular contractile effects of ergot alkaloids. Twelve adult female sheep were randomly placed into control and exposure groups (n = 6/group). Ergot sclerotia were collected and finely ground. The concentrations of six ergot alkaloids (ergocornine, ergocristine, ergocryptine, ergometrine, ergosine, and ergotamine) were determined using HPLC/MS at Prairie Diagnostic Services Inc., (Saskatoon, SK, Canada). Each ewe within the treatment group received a single oral treatment of ground ergot sclerotia at a dose of 600 µg/kg BW (total ergot) while each ewe in the control group received water. Animals were euthanized 12 h after the treatment, and the pedal artery (dorsal metatarsal III artery) from the left hind limb from each animal was carefully dissected and mounted in an isolated tissue bath. The vascular contractile response to phenylephrine (PE) (α₁-adrenergic agonist) was compared between the two groups before and after TE (α₁-adrenergic antagonist) treatment. Acute exposure to ergot alkaloids resulted in a 38% increase in vascular sensitivity to PE compared to control (Ctl EC₅₀ = 1.74 × 10⁻⁶ M; Exp EC₅₀ = 1.079 × 10⁻⁶ M, p = 0.046). TE treatment resulted in a significant dose-dependent increase in EC₅₀ in both exposure and control groups (p < 0.05 for all treatments). Surprisingly, TE effect was significantly more pronounced in the ergot exposed group compared to the control group at two of the three concentrations of TE (TE 30 nM, p = 0.36; TE 100 nM, p < 0.001; TE 300 nM, p < 0.001). Similar to chronic exposure, acute exposure to ergot alkaloids results in increased vascular sensitivity to PE. TE is a more potent dose-dependent antagonist for the PE contractile response in sheep exposed to ergot compared to the control group. This study may indicate that the dry gangrene seen in sheep, and likely other species, might be related to the activation of α₁-adrenergic receptor. This effect may be reversed using TE, especially at early stages of the disease before cell death occurs. This study may also indicate that acute-single dose exposure scenario may be useful in the study of vascular effects of ergot alkaloids.

Endophyte-Infected Tall Fescue Affects Rumen Microbiota in Grazing Ewes at Gestation and Lactation

Tall fescue (Schedonorus arundinaceus) is a cool-season perennial grass that is widely used as a forage for many livestock species including sheep. An endophyte (Neotyphodium coenophialum) in tall fescue produces ergot alkaloids that enhance plant survival but produce toxicosis in animals. The objective of this study was to investigate the rumen microbiota from gestation and lactation in ewes grazing tall fescue pastures with high (HA) or moderate (MA) levels of endophyte infection, and their relationship with serum parameters. Data were collected at the beginning of the study (d1), the week before initiation of lambing (d51), and at the end of the trial (d115). The rumen microbiota was evaluated using 16S rRNA gene sequencing. Ewes grazing HA had greater serum non-esterified fatty acid (NEFA) (P = 0.024) levels compared with ewes in MA pasture at d115. Both the number of observed OTUs and Shannon diversity index tended (P = 0.08, P = 0.06) to be greater for HA than for MA on d115. At the genus level, Prevotella relative abundance increased with time in both MA and HA (on d1, d51, and d115: 15.17, 25.59, and 24.78% in MA; 14.17, 18.10, and 19.41% in HA). Taxa unclassified at the genus level including (unclassified) Lachnospiraceae, Coriobacteriaceae, and Veillonellaceae exhibited higher abundances in HA at d51 (3.72, 2.07, and 11.22%) compared with MA (2.06, 1.28, and 7.42%). The predictor microbiota for HA and MA were identified by a random forest classification model. The HA predictors included bacteria associated with unclassified Coriobacteriaceae and Ruminococcaceae. Other OTUs classified as Prevotella and Clostridiales could be microbial predictors for MA. The OTUs classified as Prevotella and Lachnospiraceae were negatively correlated with serum concentration of prolactin. Negative correlations with NEFA were observed in the microbiota such as species affiliated to unclassified Clostridiales and Prevotella. OTUs classified as Bacteroidetes and Coriobacteriaceae exhibited a positive correlation with NEFA. Our study confirmed that the rumen microbiota populations were affected by high levels of toxins in endophyte-infected tall fescue and were associated with host hormone and energy metabolism.

Differentially expressed genes in cotyledon of ewes fed mycotoxins

BACKGROUND

Ergot alkaloids (E+) are mycotoxins produced by the endophytic fungus, Epichloë coenophiala, in tall fescue that are associated with ergotism in animals. Exposure to ergot alkaloids during gestation reduces fetal weight and placental mass in sheep. These reductions are related to vasoconstrictive effects of ergot alkaloids and potential alterations in nutrient transport to the fetus. Cotyledon samples were obtained from eight ewes that were fed E+ (n = 4; E+/E+) or E- (endophyte-free without ergot alkaloids; n = 4; E-/E-) seed during both mid (d 35 to 85) and late (d 85-133) gestation to assess differentially expressed genes associated with ergot alkaloid induced reductions in placental mass and fetal weight, and discover potential adaptive mechanisms to alter nutrient supply to fetus.

RESULTS

Ewes fed E+/E+ fescue seed during both mid and late gestation had 20% reduction in fetal body weight and 33% reduction in cotyledon mass compared to controls (E-/E-). Over 13,000 genes were identified with 110 upregulated and 33 downregulated. Four genes had a |log2FC| > 5 for ewes consuming E+/E+ treatment compared to controls: LECT2, SLC22A9, APOC3, and MBL2. REViGO revealed clusters of upregulated genes associated glucose, carbohydrates, lipid, protein, macromolecular and cellular metabolism, regulation of wound healing and response to starvation. For downregulated genes, no clusters were present, but all enriched GO terms were associated with anion and monocarboxylic acid transport. The complement and coagulation cascade and the peroxisome proliferator-activated receptor signaling pathway were found to be enriched for ewes consuming E+/E+ treatment.

CONCLUSIONS

Consumption of ergot alkaloids during gestation altered the cotyledonary transcriptome specifically related to macronutrient metabolism, wound healing and starvation. These results show that ergot alkaloid exposure upregulates genes involved in nutrient metabolism to supply the fetus with additional substrates in attempts to rescue fetal growth.

Effects of endophyte-infected tall fescue seed and protein supplementation on stocker steers: I. Growth performance and hemodynamic responses

Fescue toxicosis is a multifaceted syndrome common in cattle grazing endophyte-infected tall fescue and is detrimental to growth and performance. Recent research has shown that supplementing protein has the potential to enhance growth performance in weaned steers. Therefore, the objective of this study was to evaluate the effect of supplemental CP on physiological parameters in stocker steers experiencing fescue toxicosis. Thirty-six weaned Angus steers (6 mo of age) stratified by weight (196.1 ± 3.6 kg) were assigned to a 2 × 2 factorial arrangement for 56 d: endophyte-free (EF) seed and 14% CP (EF-14; n = 9), EF seed and 18% CP (EF-18; n = 9), endophyte-infected (EI) seed and 14% CP (EI-14; n = 9), and EI seed and 18% CP (EI-18; n = 9). Steer growth and hemodynamic responses were collected weekly during ergot alkaloid exposure. On day 14 of the trial, iButton temperature data loggers were subcutaneously inserted in the lateral neck region to record hourly body temperature for 42 d. Data were analyzed using PROC MIXED of SAS with repeated measures. No differences were observed in DMI, BW, ADG, F:G, or BCS during the treatment period (P > 0.05). Hair shedding scores, rectal temperatures, surface temperatures, and respiration rates were greater in EI steers compared to EF steers regardless of supplemental CP (P < 0.05). However, subcutaneous body temperature was greater in EI-14 steers (37.94 °C) compared to other steer groups (37.60, 37.68, 37.72 ± 0.04 °C for EF-14, EF-18, and EI-18, respectively; P < 0.05). Prolactin concentrations tended to be greater in EF steers when compared to EI steers (P = 0.07). Heart rate and hematocrit were reduced for EI-18 steers compared to other steer groups (P < 0.05). Caudal artery diameter was reduced in EI-18 steers compared to EI-14 steers (2.60 vs. 2.75 ± 0.05 mm, respectively; P < 0.05) and caudal vein diameter was reduced in EI-18 steers (3.20 mm) compared to all other steer groups (3.36, 3.39, 3.50 mm for EF-14, EF-18, and EI-14, respectively; P < 0.05). However, there was no difference observed in systolic or diastolic blood pressure during the treatment period (P > 0.05). Based on the data, exposure to low to moderate levels of ergot alkaloids during the stocker phase had a negative impact on hemodynamic responses and supplemental CP had minimal impact to alleviate symptoms. Therefore, feeding additional protein above established requirements is not expected to help alleviate fescue toxicosis.

Impact of Ergot Alkaloids on Female Reproduction in Domestic Livestock Species

Fescue toxicosis is a multifaceted syndrome that elicits many negative effects on livestock consuming ergot alkaloids produced by endophyte-infected tall fescue. The economic losses associated with fescue toxicosis are primarily due to reproductive failure including altered cyclicity, suppressed hormone secretion, reduced pregnancy rates, agalactia, and reduced offspring birth weights. For decades, a multitude of research has investigated the physiological and cellular mechanisms of these reproductive failures associated with fescue toxicosis. This review will summarize the various effects of ergot alkaloids on female reproduction in grazing livestock species.

Ergot alkaloid exposure during gestation alters. I. Maternal characteristics and placental development of pregnant ewes1

Tall fescue [Lolium arundinaceum (Scheyreb.) Darbysh] is the primary cool season forage grass in the Southeastern United States. Most tall fescue contains an endophytic fungus (Epichloë coenophiala) that produces ergot alkaloids and upon ingestion induces fescue toxicosis. The objective of this study was to assess how exposure to endophyte-infected (E+; 1.77 mg hd-1 d-1 ergovaline and ergovalinine) or endophyte-free (E-; 0 mg hd-1 d-1 ergovaline and ergovalinine) tall fescue seed fed during 2 stages of gestation (MID, days 35-85/LATE, days 86-133) alters placental development. Thirty-six, fescue naïve Suffolk ewes were randomly assigned to 1 of 4 fescue treatments: E-/E-, E-/E+, E+/E-, or E+/E+. Ewes were individually fed the same amount of E+ or E- seed mixed into total mixed ration during MID and LATE gestation. Terminal surgeries were conducted on day 133 of gestation. Ewes fed E+ fescue seed had elevated (P < 0.001) ergot alkaloid excretion and reduced (P < 0.001) prolactin levels during the periods when fed E+ seed. Ewes switched on day 86 from E- to E+ seed had a 4% reduction (P = 0.005) in DMI during LATE gestation, which translated to a 2% reduction (P = 0.07) in DMI overall. Average daily gain was also reduced (P = 0.049) by 64% for E-/E+ ewes during LATE gestation and tended to be reduced (P = 0.06) by 33% overall. Ewes fed E+ seed during LATE gestation exhibited a 14% and 23% reduction in uterine (P = 0.03) and placentome (P = 0.004) weights, respectively. Caruncle weights were also reduced by 28% (P = 0.003) for E-/E+ ewes compared with E-/E- and E+/E-. Ewes fed E+ seed during both MID and LATE gestation exhibited a 32% reduction in cotyledon (P = 0.01) weights, whereas ewes fed E+ seed only during MID gestation (E+/E-) had improved (P = 0.01) cotyledon weights. The percentage of type A placentomes tended to be greater (P = 0.08) for E+/E+ ewes compared with other treatments. Other placentome types (B, C, or D) did not differ (P > 0.05). Total fetal weight per ewe was reduced (P = 0.01) for ewes fed E+ seed during LATE gestation compared with E-; however, feeding E+ seed during MID gestation did not alter (P = 0.70) total fetal weight per ewe. These results suggest that exposure to ergot alkaloids during LATE (days 86-133) gestation has the greatest impact on placental development by reducing uterine and placentome weights. This, in turn, reduced total fetal weight per ewe by 15% in ewes fed E+ seed during LATE gestation (E-/E+ and E+/E+).

Ergot alkaloid exposure during gestation alters: II. Uterine and umbilical artery vasoactivity1

Previous research has shown that livestock exposed to ergot alkaloids results in decreased vasoactivity of gastrointestinal and peripheral vasculature. Little is known regarding the effect ergot alkaloid exposure during gestation may have on vasculature supporting the fetus. The objective of this study was to evaluate contractile responses of uterine and umbilical arteries collected from ewes consuming ergot alkaloids during gestation. On day 35 of gestation, 36 Suffolk ewes (78.24 ± 9.5 kg) were assigned to endophyte-infected (E+) or endophyte-free (E-) tall fescue seed treatments that were fed either throughout or switched on day 86 of gestation, creating four seed treatments E+E+, E+E-, E-E+, and E-E-. Ewes were fed E+ tall fescue seed to provide 1.77 mg of total ergovaline ⋅ hd-1 ⋅ d-1 with E- ewes receiving the same quantity of E- seed. Gestation was terminated on day 133, and sections of uterine artery and umbilical cord were surgically collected. Only collections from 28 ewes (n = 7/treatment) were of sufficient viability to proceed with the contractility experiments. Arteries were cleaned, sliced into 2-mm cross sections, and suspended in multi-myograph chambers containing 5 mL of continuously oxygenated Krebs-Henseleit buffer. Vessels were exposed to increasing concentrations (5 × 10-8 to 1 × 10-4 M) of norepinephrine, serotonin, ergotamine, and ergovaline (5 × 10-9 to 1 × 10-5M; extract of tall fescue seed) in 15-min intervals. Increasing concentrations of norepinephrine generated a contractile response by the uterine artery (P < 0.05), but no response in the umbilical artery. Increasing concentrations of serotonin resulted in negligible responses in uterine preparations, whereas umbilical artery preparations were responsive (P < 0.05) to serotonin. Ewes receiving E+E+ and E-E+ treatments had decreased vasoactivity in umbilical arteries to serotonin with a dextral shift in concentrations where the response curve initiated (P < 0.05). Interestingly, uterine arteries were not responsive to exposure to ergotamine or ergovaline, whereas umbilical arteries were responsive (P < 0.05). Umbilical arteries collected from ewes receiving E-E- and E+E- were more vasoactive to ergot alkaloids (P < 0.05) than other treatments. These findings indicate that maternal blood supply to the placenta appears protected from negative effects of ergot alkaloids; however, umbilical vasculature is not, and this could adversely influence fetal growth.

Interaction of ergovaline with serotonin receptor 5-HT2A in bovine ruminal and mesenteric vasculature

Ergot alkaloids from endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum) induce vasoconstriction. Previous work has shown that serotonin receptor subtype, 5HT2A, is present in bovine ruminal (R) and mesenteric (M) vasculature, plays a role in vasoconstriction, and could be influenced by ergot alkaloids. To determine the influence of ergot alkaloids on 5HT2A, the vasoactivity of an agonist selective for 5HT2A, (4-bromo-3,6-dimethoxybenzocyclobuten-1-yl) methylamine HCl (TCB-2), was evaluated using bovine ruminal and mesenteric arteries and veins (RA, RV, MA, MV) that were exposed to ergovaline (ERV) prior to or during the TCB-2 additions. Ruminal and mesenteric blood vessel segments were collected, cleaned, and cut into 2- to 3-mm cross-sections. Vessel segments were incubated in Krebs-Henseleit buffer containing 0, 0.01 or 1 µM ERV for 2 h prior to TCB-2 dose response or exposed to ERV concentrations simultaneously during TCB-2 dose response. For the dose response portion of the study, vessels were suspended in a multimyograph containing 5 mL of continuously oxygenated Krebs-Henseleit buffer and equilibrated to 1 g tension for 90 min. Vessels were exposed to increasing concentrations of TCB-2 every 15 min and contractile response data were normalized as a percentage of the maximum contractile response induced by 120 mM KCl reference. Analysis of variance was evaluated separately for each vessel and each ERV exposure experiment using the mixed models procedure of SAS for effects of TCB-2 and ERV concentrations. All blood vessels with previous ERV exposure had significantly lower contractile responses to TCB-2 (P < 0.01). All blood vessels with simultaneous exposure to 1 µM ERV had higher (P < 0.01) contractile responses at lower concentrations of TCB-2. Simultaneous ERV addition at 1 × 10-4 M TCB-2 did not affect contractility of RV, MA, MV (P > 0.05), but decreased contractility of RA (P < 0.01). These results indicate that ergopeptine alkaloid exposure influences contractility of bovine ruminal and mesenteric blood vessels through serotonin receptor subtype 5HT2A by acting as both an agonist and antagonist. Additional work is needed to determine if ergot alkaloids like ERV simply occupy receptor binding sites competitively, or influence receptor internalization to cause the observed divergent responses.

Effects of grazing different ergovaline concentrations on vasoactivity of bovine lateral saphenous vein

Previous research has demonstrated that exposure to ergot alkaloids reduces vasoactivity of serotonin (5HT) receptors. Chemical suppression of tall fescue seedhead production is a tool to reduce the level of exposure to ergot alkaloids by a grazing animal. Therefore, the objective was to evaluate contractility of lateral saphenous veins biopsied from mixed breed steers following a 87- to 101-d grazing period on 3-ha pastures of bermudagrass (Cynodon dactylon; n = 5 steers; BW = 340 ± 9 kg), or toxic endophyte-infected tall fescue (Lolium arundinaceum) that was not treated (n = 5 steers; BW = 300 ± 6; 0.56 ppm ergovaline) or was treated (n = 5 steers; BW = 294 ± 9 kg; 0.24 ppm ergovaline) with herbicide containing aminopyralid and metsulfuron-methyl. To evaluate contractility, biopsied veins were mounted in a multimyograph and exposed to increasing concentrations of a tall fescue seed extract (EXT; ergovaline source) and 5HT1B (CP 93129), 5HT1D (L-694,247), and 5HT2A (TCB2) agonists. All contractility data were normalized to a maximal response of 1 × 10-4 M norepinephrine and were analyzed as a split plot treatment design using SAS for effects of pasture treatment, agonist concentration, and the interaction. There was no contractile response to any concentration of 5HT1B agonist in any of the pasture treatments. There were pasture × concentration interactions for contractile responses to 5HT2A agonist (P < 0.01) and EXT (P < 0.01). For both EXT and TCB2, veins from bermudagrass steers were more vasoactive to the higher concentrations of these compounds (P < 0.05), and there were no differences between veins collected from the unsuppressed or seedhead-suppressed treatments (P = 0.66). There was also a pasture × concentration interaction for the contractile responses to 5HT1D agonist (P < 0.01). However, these responses were not sigmoidal and reached a zenith at 5 × 10-7 and 1 × 10-6 M. At these concentrations, the response was greatest for veins from the unsuppressed treatment (P < 0.05) and did not differ between veins from suppressed and bermudagrass treatments (P = 0.41). Although reduced levels of ergovaline in seedhead-suppressed pastures did not alter vasoactivity of 5HT2A or 5HT1B receptors in the lateral saphenous vein, elevated vasoactivity of 5HT1D in veins from unsuppressed tall fescue pasture treatment suggests that lower ergovaline levels in seedhead-suppressed pastures can influence the vascular effects of ergot alkaloids.

Pharmacologic assessment of bovine ruminal and mesenteric vascular serotonin receptor populations

Prior work using a contractility bioassay determined that the serotonin (5-HT) receptor subtype 5-HT2A is present in bovine lateral saphenous veins and plays a role in ergot alkaloid (EA)-induced vascular contraction in steers grazing endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum). Ergot alkaloids have also been shown to be vasoactive in bovine gut vasculature. To determine what 5-HT receptors are involved in vasoconstriction of gut vasculature, contractility of ruminal and mesenteric arteries and veins collected from cattle was evaluated in the presence of agonists selective for 5-HT1B (CP 93129), 5-HT1D (L-694, 247), 5-HT2A (TCB-2), 5-HT2B (BW 723C86), 5-HT4 (BIMU-8), and 5-HT7 (LP 44) receptors. Segments of ruminal and mesenteric veins and arteries were collected and suspended in a multimyograph containing continuously oxygenated Krebs-Henseleit buffer. Blood vessels were exposed to increasing concentrations of 5-HT agonists every 15 min and contractile response data were normalized as a percentage of the maximum contractile response induced by 120 mM KCl. Analysis of variance was evaluated using mixed models procedure of SAS for effects of agonist concentration for each vessel type. Receptor agonists for 5-HT2B, 5-HT1D, and 5-HT7 did not induce a contractile response for ruminal or mesenteric vasculature (P > 0.05). However, when exposed to agonists for 5-HT2B or 5-HT1D, mesenteric veins relaxed below zero (P < 0.05). Exposure of all 4 blood vessel types to 5-HT2A agonist induced contractile responses (P < 0.05). The findings of this study indicate that 5-HT1D and 5-HT2B are present in mesenteric veins and may play a role in vasorelaxation. Further, 5-HT2A is present in ruminal and mesenteric vasculature, plays a role in vasoconstriction of these vessels, and could be influenced by EA exposure as has been demonstrated in peripheral blood vessels.

Tall fescue ergot alkaloids are vasoactive in equine vasculature

Mares grazing endophyte-infected () tall fescue () typically exhibit reproductive dysfunction rather than problems associated with peripheral vasoconstriction as a primary sign of the fescue toxicosis syndrome. Research using Doppler ultrasonography demonstrated that consumption of endophyte-infected tall fescue seed causes measurable vasoconstriction in the medial palmar artery. The objective of this study was to evaluate contractile responses of medial palmar artery and vein to increasing concentrations of various tall fescue alkaloids. Medial palmar arteries and veins were collected immediately following euthanasia from 23 horses of mixed breed, age, and gender from both forelimbs, and uterine arteries were collected from females ( = 12). Vessels were separated, cleaned of excess connective and adipose tissue, divided into 2- to 3-mm cross-sections, and suspended in a multimyograph chamber with continuously oxygenated Krebs-Henseleit buffer (95% O/5% CO; pH 7.4; 37°C). Following a 90-min equilibration and recovery from reference compound exposure, increasing concentrations of norepinephrine, 5-hydroxytryptamine, ergotamine, and ergonovine for the palmar artery and vein and uterine artery and ergovaline, ergocryptine, ergocristine, ergocornine, and lysergic acid for the palmar artery and vein were added to assess vasoactivity. Data were normalized as a percentage of contractile response induced by the reference compound addition and analyzed as a completely randomized design. Both norepinephrine and serotonin were vasoactive in all 3 types of blood vessels. Neither ergotamine nor ergonovine were vasoactive in the uterine artery. All alkaloids tested with the palmar artery and vein produced a contractile response, except that neither the palmar artery nor the palmar vein responded to lysergic acid ( > 0.05). Ergovaline was the most vasoactive ergot alkaloid in both the palmar artery and the palmar vein ( < 0.05) followed by ergonovine, whereas out of the 4 remaining ergopeptine alkaloids tested, ergocristine induced the lowest contractile response. Although horses do not outwardly appear to be affected by peripheral vasoconstriction as observed in cattle, these data indicate that tall fescue alkaloids are vasoactive and suggest that potential exists for peripheral vascular effects of tall fescue alkaloids in horses. This does not appear to be the case for the uterine artery, and future research should be directed at understanding how ergot alkaloids cause equine reproductive dysfunction.

Contractile Response of Bovine Lateral Saphenous Vein to Ergotamine Tartrate Exposed to Different Concentrations of Molecularly Imprinted Polymer

Ergot alkaloids, in their active isomeric form, affect animal health and performance, and adsorbents are used to mitigate toxicities by reducing bioavailability. Adsorbents with high specificity (molecularly imprinted polymers: MIP) adsorb ergot alkaloids in vitro, but require evaluation for biological implications. Using ex vivo myography, synthetic polymers were evaluated for effects on the bioactivity of ergotamine tartrate (ETA). Polymers were first evaluated using isotherms. Lateral saphenous veins were collected from 17 steers for four independent studies: dose response of ETA, adsorbent dose response, validation of pre-myograph incubation conditions and MIP/ non-molecularly imprinted polymer (NIP) comparison. Norepinephrine normalized percent contractile response to increasing ETA exhibited a sigmoidal dose response (max: 88.47 and log of the effective molar concentration (EC50) (-log [ETA]) of 6.66 ± 0.17 M). Although sample preparation time affected contractile response (p < 0.001), pre-myograph incubation temperature (39 vs. 21 °C, 1 h) had no effect (p > 0.05). Isothermal adsorption showed a maximum adsorption of 3.27E-008 moles·mg-1 and affinity between 0.51 and 0.57 mg (R²: 0.83-0.92) for both polymers, with no significant difference between polymers (p > 0.05). No significant differences in maximum inhibitory (p = 0.96) and IC50 responses (p = 0.163) between MIP and NIP were noticed. Normalized percent contraction could be predicted from the in vitro adsorption data (R² = 0.87, p < 0.01), for both polymers. These studies indicate that synthetic polymers are potentially effective adsorbents to mitigate ergot toxicity caused by ergot alkaloids, with little evidence of significant differences between MIP and NIP in aqueous media.

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

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; 5HT_2A agonist), guanfacine (GF; α_2A-adrenergic agonist), and (R)-(+)-m-nitrobiphenyline oxalate (NBP; α_2C-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 5HT_2A receptors appear to be more dramatically affected in the lateral saphenous vein by grazing E+ tall fescue pasture than adrenergic receptors.

BILL E. KUNKLE INTERDISCIPLINARY BEEF SYMPOSIUM: Physiologic effects of ergot alkaloids: What happens when excretion does not equal consumption?

Increased persistence of tall fescue () infested with an endophytic fungus, (formerly ), in forage-based agriculture has led to increased effort in understanding the negative effects caused by consumption of ergot alkaloids by animals consuming this forage. Ergot alkaloids have been shown to have an extremely short plasma half-life, but this does not necessarily equate to total clearance. Studies that measured consumption and excretion of alkaloids have demonstrated that in the case of ergovaline, less is excreted than is consumed. The fate of ergot alkaloids that leave circulation but are not excreted is not well understood. Consequently, these "alkaloid balance studies" have led to speculation that ergovaline might bioaccumulate in the animal. Unfortunately, few data indisputably support this outcome. Progress has been slowed by the fact that the fungus produces a multitude of different ergot alkaloids that can bind to a variety of different receptors. Binding studies have shown that ergot alkaloids have unusually slow receptor dissociation rates that have been described as irreversible and contribute to a persistent signaling effect. In vitro analyses have revealed a potential for accumulation of ergot alkaloids through repetitive exposures to low concentrations creating a "depot" of alkaloids available to interact with receptors. The specific high binding affinity of ergot alkaloids combined with the potential turnover of alkaloids bound nonspecifically could extend residual effects of these compounds. Interestingly, cattle exposed to ergot alkaloids in vivo have a consistently lower vascular response to agonists that target receptors known to bind ergot alkaloids. If these same receptors are blocked with an antagonist, contractile response to ergopeptine alkaloids is also reduced significantly (>60% reduction). This observation that alkaloid exposure interrupts normal function of a receptor can persist 5 to 6 wk after animals have been removed from an ergot alkaloid source (and prolactin levels have long since returned to normal). Thus, clearance of ergot alkaloids from cattle grazing pasture with ergot alkaloid-producing endophytes may occur in a similar gradual manner. Studies that improve the understanding of how cattle process ergot alkaloids will help answer the question of whether ergot alkaloids bioaccumulate.

Ergovaline, an endophytic alkaloid. 1. Animal physiology and metabolism

Ergovaline is an ergot alkaloid found in some endophyte-infected ryegrasses and it has been implicated in the expression of ergotism-like symptoms of grazing livestock, as well as in the protection of the plant against invertebrate predation and abiotic stresses. These selection pressures have resulted in a conflict between the needs of the pasture for persistence and the needs of the animal for production. Ergovaline has not been well studied in terms of animal physiology until recently. There are several putative mechanisms that limit the bioavailability of ergovaline, ranging from microbial biotransformation to post-absorptive hepatic detoxification. Although there are mechanisms that protect the animal from ergovaline exposure, tissues are very sensitive to ergovaline, indicating that ergovaline is very potent and that small quantities have the potential to cause noticeable physiological effects. The range of physiological effects, including decreased circulating prolactin, vasoconstriction and increased susceptibility to heat stress are all linked to the interaction of ergovaline with biogenic amine receptors found throughout the body. This review will focus on understanding the variation of ergovaline concentration in terms of bioavailability, the myriad of hurdles a molecule of ergovaline must overcome to cause an effect, what the ergovaline-induced effects are in New Zealand livestock and how this relates to the potency of ergovaline.

Interaction of Isoflavones and Endophyte-Infected Tall Fescue Seed Extract on Vasoactivity of Bovine Mesenteric Vasculature

It was hypothesized that isoflavones may attenuate ergot alkaloid-induced vasoconstriction and possibly alleviate diminished contractility of vasculature after exposure to ergot alkaloids. The objective of this study was to determine if prior incubation of bovine mesenteric vasculature with the isoflavones formononetin (F), biochanin A (B), or an ergovaline-containing tall fescue seed extract (EXT) and their combinations affect ergotamine (ERT)-induced contractility. Multiple segments of mesenteric artery and vein supporting the ileal flange of the small intestine were collected from Angus heifers at slaughter (n = 5, bodyweight = 639 ± 39 kg). Duplicates of each vessel type were incubated in tissue culture flasks at 37°C with a 50-mL volume of Krebs–Henseleit buffer containing: only buffer (control); or 1 × 10⁻⁶ M EXT; F; or B; and combinations of 1 × 10⁻⁶ M EXT + F; 1 × 10⁻⁶ M EXT + B; 1 × 10⁻⁶ M F + B; or 1 × 10⁻⁶ M EXT + F + B. After incubation for 2 h, sections were mounted in a multimyograph chamber. The ERT dose responses were normalized to 0.12 M KCl. Pretreatment with F, B, and F + B without EXT resulted in similar contractile responses to ERT in mesenteric artery and all incubations containing EXT resulted in a complete loss of vasoactivity to ERT. In mesenteric artery pretreated with EXT, treatments that contained B had higher contractile responses (P < 0.05) at ERT concentrations of 1 × 10⁻⁷ and 5 × 10⁻⁷ M. Also, treatments containing B tended (P < 0.1) to have greater responses than treatments without B at ERT concentrations of 1 × 10⁻⁶, 5 × 10⁻⁶, and 5 × 10⁻⁵ M. In mesenteric vein pretreated with EXT, treatments containing F had greater contractile responses to ERT at 1 × 10⁻⁵, 5 × 10⁻⁵, and 1 × 10⁻⁴ M (P < 0.05). These data indicated that F and B at 1 × 10⁻⁶ M and their combination did not impact the overall contractile response to ERT in mesenteric vasculature. However, F and B may offset some of the vasoconstriction caused by prior exposure to ergot alkaloids.

Rhodococcus erythropolis MTHt3 biotransforms ergopeptines to lysergic acid

Background

Ergopeptines are a predominant class of ergot alkaloids produced by tall fescue grass endophyte Neotyphodium coenophialum or cereal pathogen Claviceps purpurea. The vasoconstrictive activity of ergopeptines makes them toxic for mammals, and they can be a problem in animal husbandry.

Results

We isolated an ergopeptine degrading bacterial strain, MTHt3, and classified it, based on its 16S rDNA sequence, as a strain of Rhodococcus erythropolis (Nocardiaceae, Actinobacteria). For strain isolation, mixed microbial cultures were obtained from artificially ergot alkaloid-enriched soil, and provided with the ergopeptine ergotamine in mineral medium for enrichment. Individual colonies derived from such mixed cultures were screened for ergotamine degradation by high performance liquid chromatography and fluorescence detection. R. erythropolis MTHt3 converted ergotamine to ergine (lysergic acid amide) and further to lysergic acid, which accumulated as an end product. No other tested R. erythropolis strain degraded ergotamine. R. erythropolis MTHt3 degraded all ergopeptines found in an ergot extract, namely ergotamine, ergovaline, ergocristine, ergocryptine, ergocornine, and ergosine, but the simpler lysergic acid derivatives agroclavine, chanoclavine, and ergometrine were not degraded. Temperature and pH dependence of ergotamine and ergine bioconversion activity was different for the two reactions.

Conclusions

Degradation of ergopeptines to ergine is a previously unknown microbial reaction. The reaction end product, lysergic acid, has no or much lower vasoconstrictive activity than ergopeptines. If the genes encoding enzymes for ergopeptine catabolism can be cloned and expressed in recombinant hosts, application of ergopeptine and ergine degrading enzymes for reduction of toxicity of ergot alkaloid-contaminated animal feed may be feasible.

Development of a methodology to measure the effect of ergot alkaloids on forestomach motility using real-time wireless telemetry

The objectives of these experiments were to characterize rumen motility patterns of cattle fed once daily using a real-time wireless telemetry system, determine when to measure rumen motility with this system, and determine the effect of ruminal dosing of ergot alkaloids on rumen motility. Ruminally cannulated Holstein steers (n = 8) were fed a basal diet of alfalfa cubes once daily. Rumen motility was measured by monitoring real-time pressure changes within the rumen using wireless telemetry and pressure transducers. Experiment 1 consisted of three 24-h rumen pressure collections beginning immediately after feeding. Data were recorded, stored, and analyzed using iox2 software and the rhythmic analyzer. All motility variables differed (P < 0.01) between hours and thirds (8-h periods) of the day. There were no differences between days for most variables. The variance of the second 8-h period of the day was less than (P < 0.01) the first for area and less than the third for amplitude, frequency, duration, and area (P < 0.05). These data demonstrated that the second 8-h period of the day was the least variable for many measures of motility and would provide the best opportunity for testing differences in motility due to treatments. In Experiment 2, the steers (n = 8) were pair-fed the basal diet of Experiment 1 and dosed with endophyte-free (E−) or endophyte-infected (E+; 0 or 10 μg ergovaline + ergovalinine/kg BW; respectively) tall fescue seed before feeding for 15 d. Rumen motility was measured for 8 h beginning 8 h after feeding for the first 14 d of seed dosing. Blood samples were taken on d 1, 7, and 15, and rumen content samples were taken on d 15. Baseline (P = 0.06) and peak (P = 0.04) pressure were lower for E+ steers. Water intake tended (P = 0.10) to be less for E+ steers the first 8 h period after feeding. The E+ seed treatment at this dosage under thermoneutral conditions did not significantly affect rumen motility, ruminal fill, or dry matter of rumen contents.

Exposure to ergot alkaloids during gestation reduces fetal growth in sheep

Tall fescue [Lolium arundinaceum (Schreb.) Darbysh; Schedonorus phoenix (Scop.) Holub] is the primary cool season perennial grass in the eastern U.S. Most tall fescue contains an endophyte (Neotyphodium coenophialum), which produces ergot alkaloids that cause vasoconstriction and could restrict blood flow to the fetus in pregnant animals. The objective of this study was to examine fetal growth during maternal exposure to ergot alkaloids during gestation. Pregnant ewes (n = 16) were randomly assigned to one of two dietary treatments: (1) endophyte-infected (N. coenophialum) tall fescue seed (E+; 0.8 ug of ergovaline /g diet DM) and (2) endophyte-free tall fescue seed (E−; 0.0 ug of ergovaline/g diet DM). Birth weight of lambs was reduced by 37% for E+ compared to E−. Organ and muscle weights were also lighter for E+ than E−. Exposure to ergot alkaloids in utero reduces fetal growth and muscle development.

Dietary exposure to ergot alkaloids decreases contractility of bovine mesenteric vasculature

Ergot alkaloids are hypothesized to cause vasoconstriction in the midgut, and prior exposure may affect the vasoactivity of these compounds. The objectives of this study were to profile vasoactivity of ergot alkaloids in bovine mesenteric artery (MA) and vein (MV) and determine if previous exposure to endophyte-infected tall fescue seed affected vasoactivity of ergocryptine (ERP), ergotamine (ERT), ergocristine (ERS), ergocornine (ERO), ergonovine (ERN), lysergic acid (LSA), ergovaline-containing tall fescue seed extract (EXT), and 5-hydroxytryptamine (5HT; serotonin). Ruminally cannulated Angus steers (n = 12; BW = 547 ± 31 kg) were paired by weight and randomly assigned to 6 blocks. Steers were ruminally dosed daily with 1 kg of either endophyte-infected (E+; 4.45 mg ergovaline/kg DM) or endophyte-free (E-; 0 mg ergovaline/kg DM) tall fescue seed for 21 d before slaughter. Branches of MA and MV supporting the cranial portion of the ileum were collected after slaughter on d 22, placed in a modified Krebs-Henseleit buffer on ice, cleaned, sectioned, and mounted in a multimyograph chamber. Contractile response was normalized to a maximum KCl response. Inner diameter (P = 0.04) and outer diameter (P = 0.02) of MA were smaller for E+ steers than E- steers. Maximum contractile responses to 120 mM KCl were not different between seed treatments in MA (P = 0.33; E-: 2.67 ± 0.43 g; E+: 3.33 ± 0.43 g) or MV (P = 0.26; E-: 2.01 ± 0.18 g; E+: 1.81 ± 0.18 g). Steers receiving E+ had a smaller (P < 0.01) MA contractile response than E- steers to ERP, ERT, ERS, ERO, ERN, EXT, and 5HT. Steers receiving E+ had a smaller (P < 0.05) MV contractile response than E- steers to ERP, ERT, ERS, ERN, EXT, and 5HT. Lysergic acid failed to induce a contractile response in MA and MV. The contractile response in MA and MV of E- steers produced by 5HT was very large. The EXT was the most potent (P < 0.05) agonist in MV and MA of E+ steers. These data showed that ergot alkaloids were vasoactive in the bovine midgut, and steers exposed to E+ had diminished contractility to some ergot alkaloids in small intestinal vasculature. The findings of this study suggest that dietary exposure to ergot alkaloids has the potential to alter nutrient absorption from the midgut by decreasing blood flow to and from the midgut due to vasoconstriction.

NutriPhysioGenomics applications to identify adaptations of cattle to consumption of ergot alkaloids and inorganic versus organic forms of selenium: altered nutritional, physiological and health states?

NutriPhysioGenomics (NPG) seeks to measure nutrition-responsive genome expression during specific physiological states, thus defining how a given challenge alters the ‘basal’ transcriptome. Application of NGS regimens (transcriptome and bioinformatics analyses) in combination with targeted-gene approaches has revealed cellular mechanisms putatively responsible for complex, whole-animal, metabolic syndromes such as heat stress and subacute ruminal acidosis. Using similar approaches, our laboratory sought to understand how the basal physiology of developing cattle adapted to two prevalent health challenges of forage-based beef cattle production in south-eastern USA: fescue toxicosis and selenium (Se) deficiency. In Model 1, pituitary and hepatic genomic expression profiles of growing beef steers grazing high (E+, n = 9) versus low (E–, n = 10) endophyte-infected tall fescue pastures for 85 days, and consuming sodium selenite (ISe) as a free-choice Se supplement, were compared by a combination of microarray, bioinformatic, and targeted-gene/protein (real-time reverse transcription–PCR, Nanostring, immunoblot) analyses. In Model 2, hepatic genomic expression profiles of growing beef heifers (0.5 kg gain/day) fed a cotton seed hull-based diet and different sources (n = 9) of dietary Se (3 mg/day) supplements (no supplement, Control; inorganic Se, sodium selenite, ISe; organic Se, Sel-Plex; OSe), or a 1.5 mg : 1.5 mg blend of ISe and OSe, MIX) were compared after 168 days of supplementation, as described for Model 1. The results for Model 1 showed, that in the pituitary of E+ steers, expression of genes for prolactin signalling; redox capacity; regulation of lactotroph, gonadotroph, and thyrotroph proliferation; gonadotropin-releasing hormone-mediated signalling; and Se-based metabolism was impaired. Concomitantly, the livers of E+ steers had an increased level of expression of genes encoding proteins responsible for shunting of amino acid carbons into pyruvate and ATP synthesis capacity (oxidative phosphorylation pathway, mitochondrial mass), increased serine and proline biosynthesis, and reduced selenoprotein-mediated metabolism. Result for Model 2 showed that, overall, there were clear differences in the profiles of differentially expressed genes (DEG) among the four Se treatment groups, with the form of Se administered being more reflective of DEG profiles than the total amount of Se assimilated. Moreover, hepatic transcriptomes profiles of MIX heifers revealed an increased potential for selenoprotein synthesis and selenoprotein-mediated metabolism. In addition, several genes involved with increased redox capacity were upregulated in MIX versus ISe heifers. Taken together, our NGS approach characterised adaptation to physiological challenges and, serendipitously, identified suppression of several metabolic pathways by consumption of ergot alkaloid consumption that have the potential to be increased with supplementation of the MIX form of Se.

Postgraze assessment of toxicosis symptoms for steers grazed on toxic endophyte-infected tall fescue pasture

A 2-yr pen experiment was conducted using 12 different crossbred Angus steers each year to determine if short-term changes in prolactin concentrations, body temperature, and vasoconstriction reflect recovery from fescue toxicosis after steers that previously grazed toxic endophyte (Neotyphodium coenophialum)-infected Kentucky 31 tall fescue [Lolium arundinaceum (Schreb.) Darbysh] are placed on nontoxic feed. Groups of 6 steers from toxic endophyte-infected and endophyte-free tall fescue grazing treatments were blocked by BW for assignment to pens as a randomized complete block design with 2 replications. Two environments were implemented by initiating the experiment on 18 August in yr 1 and on 8 September in yr 2 for durations of 30 and 21 d, respectively. Rectal temperatures were recorded, jugular blood was collected for assaying serum prolactin, and cross sections of the caudal artery were ultrasonically imaged at selected time points to evaluate temporal changes in the response variables. Rectal temperatures in steers on the toxic endophyte pasture treatment declined (P < 0.05) linearly over time in yr 1 and 2 and were similar (P > 0.10) to those on endophyte-free treatment on d 30 in yr 1 and by d 15 in yr 2. Prolactin concentrations in steers on the toxic endophyte pasture treatment showed curvilinear increases (P < 0.05) over time and were similar (P > 0.10) to steers on the endophyte-free treatment by d 15 in yr 1 and by d 10 in yr 2. Luminal areas of the caudal artery in toxic endophyte steers were less (P < 0.05) than those in endophyte-free steers across all dates in both years. Results indicated that rectal temperatures in steers after they are removed from toxic fescue may decrease over time, but temporal changes in rectal temperatures could be affected more by prevailing ambient temperatures than by actual mitigation of fescue toxicosis. Prolactin concentrations in steers after they are removed from toxic endophyte tall fescue can increase and stabilize in less than 2 wk, but alkaloid-induced vasoconstriction that causes a vulnerability to severe heat stress is not alleviated within 30 d.

Antagonism of lateral saphenous vein serotonin receptors from steers grazing endophyte-free, wild-type, or novel endophyte-infected tall fescue

Pharmacologic profiling of serotonin (5HT) receptors of bovine lateral saphenous vein has shown that cattle grazing endophyte-infected (Neotyphodium coenophialum) tall fescue (Lolium arundinaceum) have altered responses to ergovaline, 5HT, 5HT2A, and 5HT7 agonists. To determine if 5HT receptor activity of tall fescue alkaloids is affected by grazing endophyte-free (EF), wild-type [Kentucky-31 (KY31)], novel endophyte AR542-infected (MAXQ), or novel endophyte AR584-infected (AR584) tall fescue, contractile responses of lateral saphenous veins biopsied from cattle grazing these different fescue-endophyte combinations were evaluated in presence or absence of antagonists for 5HT2A (ketanserin) or 5HT7 (SB-269970) receptors. Biopsies were conducted over 2 yr on 35 mixed-breed steers (361.5 ± 6.3 kg) grazing EF (n = 12), KY31 (n = 12), MAXQ (n = 6), or AR584 (n = 5) pasture treatments (3 ha) between 84 and 98 d (Yr 1) or 108 to 124 d (Yr 2). Segments (2 to 3 cm) of vein were surgically biopsied, sliced into 2- to 3-mm cross-sections, and suspended in a myograph chamber containing 5 mL of oxygenated Krebs-Henseleit buffer (95% O2/5% CO2; pH = 7.4; 37°C). Veins were exposed to increasing concentrations of 5HT, ergovaline, and ergovaline + 1 × 10(-5) M ketanserin or + 1 × 10(-6) M SB-269970 in Yr 1. In Yr 2, ergotamine and ergocornine were evaluated in presence or absence of 1 × 10(-5) M ketanserin. Contractile response data were normalized to a reference addition of 1 × 10(-4) M norepinephrine. In Yr 1, contractile response to 5HT and ergovaline were least (P < 0.05) in KY31 pastures and the presence of ketanserin greatly reduced (P < 0.05) the response to ergovaline in all pastures. However, presence of SB-269970 did not (P = 0.91) alter contractile response to ergovaline. In Yr 2, there was no difference in contractile response to ergotamine (P = 0.13) or ergocornine (P = 0.99) across pasture treatments, but ketanserin reduced (P < 0.05) the contractile response to both alkaloids. The 5HT2A receptor is involved in alkaloid-induced vascular contraction and alkaloid binding may be affected by exposure to different endophyte-fescue combinations.