Fescue Toxicosis Research Articles

Replacing Toxic Tall Fescue With a Nontoxic Forage

Tall fescue is among the most popular cool‐season pasture grasses in the United States and is widely grown in other countries with temperate climates. In the United States, nearly all tall fescue pastures planted before 1980 are infected with Epichloë coenophialum, a microscopic fungus. The common strain of this fungus produces toxins called “ergot alkaloids,” such as ergovaline. These ergot alkaloids cause fescue toxicosis, a severe livestock disorder that costs U.S. livestock producers at least $1 billion each year. At present, there is no medical cure for fescue toxicosis. There are, however, proven management strategies that lessen the effect of toxicosis. One is the replacement of toxic tall fescue with varieties that are endophyte‐free or contain novel endophytes. Earn 1 CEU in Integrated Pest Management by reading this article and taking the quiz at https://web.sciencesocieties.org/Learning‐Center/Courses.

Cover Image, Volume 56, Issue 3

Crops & SoilsVolume 56, Issue 3 p. i-i COVER IMAGEFree Access Cover Image, Volume 56, Issue 3 First published: 12 May 2023 https://doi.org/10.1002/crso.20280AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Graphical Abstract Tall fescue is among the most popular cool-season pasture grasses in the United States and is widely grown in other countries with temperate climates. In the United States, nearly all tall fescue pastures planted before 1980 are infected with Epichloë coenophialum, a microscopic fungus. The common strain of this fungus produces toxins called “ergot alkaloids,” such as ergovaline. These ergot alkaloids cause fescue toxicosis, a severe livestock disorder that costs U.S. livestock producers at least $1 billion each year. At present, there is no medical cure for fescue toxicosis. There are, however, proven management strategies that lessen the effect of toxicosis. One is the replacement of toxic tall fescue with varieties that are endophyte-free or contain novel endophytes. See page 4. Photo courtesy of Adobe Stock/jackienix. Volume56, Issue3May–June 2023Pages i-i RelatedInformation

Effects of endophyte-infected tall fescue on performance of genotyped pregnant beef cows supplemented with rumen-protected niacin

A total of 28 Angus × Simmental pregnant dams (11 cows and 17 heifers) were selected based on genetic resistance to fescue toxicosis based on a commercial genetic test (T-snip™, Ag. Botanica, Columbia, MO). Subsequently, dams were divided based on genetic resistance to fescue toxicosis and randomly assigned to dietary treatments: 1) Susceptible Control (SC; n = 7); 2) Susceptible Niacin (SN; n = 7); 3) Tolerant Control (TC; n = 7); and 4) Tolerant Niacin (TN; n = 7). All animals received 1.16 kg of endophyte-infected (E+) tall fescue seeds for a period of 30 days. Ergovaline concentration in fescue seeds was ∼5,000 ppb on a DM basis. Dams in SN and TN groups received 6 g/hd/day as-fed of top-dressed rumen-protected niacin, following manufacturer's maximum dose recommendation. Dams in the TN group experienced an accelerated reduction in BW as compared to the rest of the treatments. However, TN offspring did not show BW differences at birth or weaning as compared to those born to dams in other treatments. Milk production was estimated by the weigh-suckle-weigh method, and no difference was observed among treatments. All dams had a reduction in circulating prolactin concentration, indicating that all animals were experiencing fescue toxicosis. In addition, blood metabolites that indicate liver health status were markedly decreased at the end of the study. Overall, these results suggest that dams receiving E+ tall fescue seeds were effectively exposed to fescue toxicosis symptoms. Nevertheless, neither rumen-protected niacin supplementation nor genetic test for resistance to fescue toxicosis could be used as an efficient mechanism of dampening these symptoms.

Condensed Tannins Attributes: Potential Solution to Fescue Toxicosis?

Tall fescue (Schedonorus arundinaceous (Schreb.) Dumort. nom. cons. Lolium arundinaceum (Schreb.) Darbysh.) toxicosis results from the consumption of alkaloids released by wild-type endophytes (Epichloe coenophiala) that live in symbiosis with the plant. Alkaloid consumption causes significant production and reproductive losses which cost the U.S. beef industry approximately $2 billion every year. Incorporating species that contain condensed tannins (CTs) into forage systems may be an effective strategy to reduce the effects of fescue toxicosis in livestock. It has been hypothesized that stable complexes formed between CTs and toxic alkaloids could help reduce their absorption through the gastrointestinal epithelia, thus reducing their toxic effects. However, it is not yet clear whether CTs are effective in reducing the effects of fescue toxicosis in grazing systems. A comprehensive literature search was carried out using Google Scholar to identify studies relevant to the research question, from which the cited articles were selected. This review covers the value and issues of tall fescue employed as useful forage, summarizes the impact endophyte-infected tall fescue can have on cattle, and sets out the current management strategies implemented to minimize fescue toxicosis. The review continues with a brief summary of tannin structure and the well-documented benefits that CT-containing forages can contribute to the productivity and sustainability of ruminant agriculture. Finally, a summary of the potential forage sources, mechanisms, and benefits of CTs in reducing the negative post-ingestion effects of fescue alkaloids in livestock is provided.

Effect of Quebracho Tannin (Schinopsis quebracho-colorado (Schltdl.) F.A. Barkley and T. Meyer) on Silage Nutritive Value, Ergovaline Concentration, and Fermentation Parameters of Tall Fescue (Schedonorus arundinaceus (Shreb.) Dumort) with Two Dry-Matter Levels

Tall fescue (Schedonorus arundinaceus (Shreb.) Dumort) is a cool-season forage grown in the mid-south United States of America that has the potential for spring silage. Ergovaline produced by the fungal endophyte Neotyphodium coenophialum is preserved in tall fescue silage and can induce tall fescue toxicosis in livestock. Condensed tannins, such as quebracho (Schinopsis quebracho-colorado (Schltdl.) F.A. Barkley and T. Meyer) extract, can bind to the nitrogenous components of ergovaline, rendering it ineffective in the ruminant. Quebracho tannin (QT) can also bind to crude protein, reducing its conversion to ammonia. Quebracho tannin was either not added (0QT) or added at 10 (10QT) or 20 (20QT) g/kg of dry matter (DM) of silage to chopped endophyte-infected tall fescue of 670 g/kg of moisture (high moisture, HM) and 440 g/kg of moisture (low moisture, LM). A moisture × QT interaction affected the final pH (p = 0.02), with the lowest pH observed in HM silages with 0QT and 10QT. The ergovaline concentrations were not significantly different (p = 0.19) among the post-ensiled forages. Ammonia concentrations (g/kg DM) were affected by a moisture × QT interaction (p = 0.05), with greater concentrations observed in HM 0QT compared with HM 10QT, HM 20QT, and LM 20QT. Lactic acid concentrations (g/kg DM) decreased (p = 0.05) with the addition of QT. The moisture × QT interaction (p = 0.02) resulted in higher concentrations of acetic acid in the HM silages with 0QT and 20QT compared to the LM silage with 20QT. The total acid concentrations (g/kg DM) were higher (p < 0.01) at HM but did not differ (p = 0.54) across the QT concentrations. Ensiling tall fescue with quebracho tannin did not reduce the ergovaline concentrations, although proteolysis was reduced at the inclusion of 10 g/kg of QT in the HM silages and 20 g/kg of QT in the LM silages. The results indicate that QT as a tall fescue silage additive showed promise for modifying silage characteristics but it did not reduce ergovaline concentrations at the low QT levels used in this study.

Conventional loose mineral with added red clover leaf (Trifolium pratense L.) reverses vasoconstriction associated with tall fescue toxicosis in steers

Endophyte-infected tall fescue (E + TF) can cause persistent vasoconstriction in ruminants and consequently fescue toxicosis. Legumes, including red clover (RC), contain isoflavones that are known hypotensive agents. Previous experiments have shown the benefits of overseeding RC or feeding other stored legumes on blood flow and growth performance of livestock challenged with E + TF; however, alternative supplementation strategies have not been explored. Therefore, the objective was to determine if low levels of RC in conventional loose mineral could mitigate fescue toxicosis symptoms. Mature, rumen fistulated steers (n = 12) received 1 of 4 mineral treatments (5 oz head d−1 or 141.8 g head d−1 dosed intraruminally; n = 3 steers per treatment): 1) 0% RC (w/w), 2) 10% RC, 3) 15% RC, or 4) 20% RC. All steers were first adapted to their basal diet (ad libitum corn silage + 2.27 kg dried distillers’ grains with solubles) for 14-days and then were subjected to a 14-day E + TF seed step-up challenge (day 0–7: 10 µg kg BW−1 ergovaline + ergovalanine [ERV]; day 8–14: 15 µg kg BW−1 ERV), followed by a 7-day withdrawal period. The caudal artery of each steer was imaged repeatedly over the course of the study using Doppler ultrasonography to monitor artery luminal areas (CAA). Jugular blood samples were serially collected to monitor serum prolactin concentrations. Data were analyzed by repeated measures using the mixed procedure of SAS with significance set at P < 0.05. A treatment by sample day interaction was detected for CAA (P = 0.0051) and prolactin (P = 0.0148). The E + TF seed challenge induced vasoconstriction (d1: −54.6%, d7: −26.8%, d14: −80.1%, relative to baseline) and prolactin depression (d7: −35.5%, d14: −83.3%, relative to baseline) in 0% RC steers (P < 0.05, in all cases). All three RC mineral treatments were effective at partially or fully alleviating vasoconstriction and prolactin depression with the 20% RC treatment being most effective on day 14 (CAA: 10% RC: +37.4%; 15% RC: +29.7%; 20% RC: +56.9%, prolactin: 10% RC: +125.3%; 15% RC: +132.1%; 20% RC: +149.2%, relative to 0% RC; P < 0.05, in all cases). All treatments fully recovered (above baseline) by the end of the withdrawal period (P < 0.05, in all cases). These results demonstrate that loose mineral amended with RC could be used to prevent the adverse effects of fescue toxicosis in E + TF grazing livestock. Additional experiments are required to determine the optimum isoflavone source and concentration required to mitigate fescue toxicosis.

Using supplemental condensed tannin to mitigate tall fescue toxicosis in non-pregnant, non-lactating ewes consuming tall fescue silage

Tall fescue [Schedonorus arundinaceus (Shreb.)], the primary grazing forage in the mid-south, and has a symbiotic relationship with an endophytic fungus (Neotyphodium coenophialum) that produces ergot alkaloids that cause fescue toxicosis in grazing livestock. Some evidence indicates that condensed tannins (CT) can bind to ergot alkaloids and render them ineffective, thereby preventing symptoms of fescue toxicosis. Non-pregnant, non-lactating ewes [n = 20; 57 ± 1.3 kg initial body weight (BW)] were housed in individual pens (1 × 1.5 m) with metal grate flooring. Ewes were offered ad libitum access to either novel endophyte (NE) or toxic endophyte-infected tall fescue silage with no CT (E0), or CT at 10 (E10) or 30 (E30) g/kg of silage dry matter (DM). The CT used was Quebracho tannin (Schinopsis quebracho-colorado). All ewes received 4 g/kg BW liquid molasses, and this served as the carrier for the CT treatments. The study consisted of 2, 21-d periods with a 30-d washout between periods. A 14-d adaption was followed by 7-d of total fecal and urine collection in each period. Blood samples for prolactin analysis were taken on the last day of each period. Data were analyzed using individual ewe within period as the experimental unit, treatment was a fixed effect, and period and pen were random effects. Prolactin was lesser (P < 0.01) in endophyte infected silage treatments. Intake (DMI; g/kg BW) and neutral detergent fiber (aNDF) intake (g/kg BW) were greater (P = 0.05) in NE compared to other treatments. Dry matter digestibility (DMD; g/kg DMI) and aNDF digestibility (g/kg NDF) were greater (P = 0.01) in NE compared to other treatments and organic matter (OM) digestibility [(OMD, g/kg OM intake (OMI)] did not differ between NE and E10, but NE was greater (P = 0.01) than E0 and E30. Digestible DMI and OMI (g/kg BW) were greater (P = 0.01) from NE compared to other treatments. Apparent N absorbed (g/kg N intake) was greater (P = 0.03) in NE, E0, and E10 compared with E30. Fecal N (g/kg N intake) was greater in E30 compared to E0 and E10, but not different from NE. Nitrogen retained (g/kg N intake and N absorbed) did not differ (P ≥ 0.31) among treatments. Condensed tannin supplementation at 30 g/kg DM had negative impacts on DM and OM digestibility and did not prevent decreases in prolactin associated with tall fescue toxicosis.

Fescue toxicosis: a detrimental condition that requires a multiapproach solution.

Fescue toxicosis: a detrimental condition that requires a multiapproach solution.

Perennial Warm-Season Grass Forages Impact on Cow-Calf Profitability in the Fescue Belt

Incorporating a perennial warm- season grass (WSG) into tall fescue (Lolium arundina-ceum [Schreb.] Darbysh.) forage systems in the fescue belt can help avoid the effects of fescue toxicosis on beef cattle (Bos taurus) reproduction and animal performance and provide forage during summer when fescue production is low. However, little information is available on the economics of incorporating WSG into fescue-based forage systems. We developed a simulation model to compare profitability of three forage systems—100% tall fescue, 70% tall fescue/30% bermudagrass (Cynodon dactylon), and 70% tall fescue/ 30% switchgrass (Panicum virgatum)—while also comparing spring- and fall-calving sea-sons on model beef cattle cow-calf operations in the fescue belt. Incorporating switch-grass increased profitability of tall fescue forage systems in both spring- and fall- calving herds, while adding bermudagrass increased profitability in spring-calving herds but not fall-calving herds. Spring-calving herds benefited the most from incorporating WSG, with profitability increases of $877 and $372 per hectare for switchgrass and bermudagrass, respectively, over the 100% tall fescue system. The order of profitability of forage systems did not change with randomly simulated decreases in rainfall and associated increased hay- feeding days, but with annual rainfall >88% of the long- term average, fall- calving 100% tall fescue was more profitable than fall- calving 70% tall fescue/30% bermuda grass. Of the scenarios modeled, the results of the simulation suggest that a profit-maximizing producer would utilize a 70% tall fescue/30% switchgrass forage system.

280 The Effect of Bromocriptine Mesylate and Heat Stress on Innate and Adaptive Immune Function in Beef Cattle

Abstract Injection of bromocriptine mesylate has been used to mimic the symptoms of tall fescue toxicosis in beef cattle. Twelve steers (351 ± 11.82 kg) were used to investigate the effect of bromocriptine mesylate and heat stress on serum prolactin, rectal temperature, respiration rate, and innate/adaptive immune function. Steers were randomly assigned to receive an injection of saline (CON) or bromocriptine mesylate (BROMO; 0.1mg/kg BW) every three days. Animals were housed for 22 d in the Brody Climatology Laboratory at thermoneutrality (TN; 19.5±0.26°C; 10-d) before transitioning (2-d) to heat stress (HS; 27.2±0.26°C nighttime, 34.5±0.26°C daytime; 10-d). Cattle were fed 1.8% of BW (DM-basis) daily across two feedings. Rectal temperatures and respiration rates were measured daily at 0600, 0900, 1500, and 1800 h. Serum and plasma were harvested from blood collected on d 1, 9, and 21 (9th d of thermoneutrality and heat stress, respectively) and analyzed for prolactin and cytokines. Dry-matter intake was not affected by treatment (P=0.52) or temperature (P=0.78). Prolactin concentrations decreased (P=0.02) throughout the trial and decreased (P&amp;lt; 0.01) with BROMO. Rectal temperature and respiration rate were greater (P&amp;lt; 0.01) for BROMO during TN and HS. Rectal temperature and respiration rate were increased (P&amp;lt; 0.01) during HS. Pro-inflammatory cytokine (TNF-α, IFN-α, IFN-γ, IL-1α, IL-1β, IL-17, and IL-18) concentrations were greater (P&amp;lt; 0.01) for BROMO steers than CON. Heat stress increased (P&amp;lt; 0.01) pro-inflammatory cytokines with the exception of IL-18 (P=0.98) regardless of treatment. Anti-inflammatory cytokines (IL-13, IL-1-F5, IL-21, IFN-β, LIF) were decreased (P&amp;lt; 0.07) for BROMO steers with the exception of IL-10 (P=0.58). Regardless of treatment IL-13, IL-21, IL-10, and LIF concentrations were greater (P&amp;lt; 0.05) during HS. These results demonstrate that bromocriptine mesylate successfully mimicked the symptoms of fescue toxicosis. Innate and adaptive immune responses were influenced by treatment and temperature, potentially affecting beef cattle immune competency.

283 Quercetin Antagonizes Tall Fescue Toxicosis-Induced Cardiovascular Toxicity in Lamb (Ovis Aries) via Modulating PGC-1α Mediated Mitochondrial Biogenesis

Abstract Quercetin is a natural flavonoid with a higher antioxidant capacity and anti-inflammatory. Tall fescue [Schedonorus arundinaceus (Schreb.) Dumort; E+] is perennial cool-season grass for grazing livestock in North America. Fescue infected with the endophyte (Neotyphodium coenophialum) produces chemicals toxic to livestock. However, the impact of quercetin on alleviating fescue toxicosis has received only limited attention. The objective of this experiment was to investigate the mitigation effect of quercetin on fescue toxicosis-induced cardiotoxicity of lambs. A total number of 24 Dorper lambs were randomized to four groups (n = 6 per group) and grazed tall fescue seed for 42 days. The results indicated that quercetin treatment alleviated fescue toxicosis induced cardiovascular histopathology injury (Fig 1), inhibited the increased trend of creatine kinase activities, and serum prolactin concentrations (Fig 2). Meanwhile, quercetin mitigated fescue toxicosis-induced cardiovascular oxidative damage by decreasing MDA and H2O2 contents, increasing antioxidant enzymes (T-SOD, Cu-Zn SOD, CAT, and T-AOC) activities (Fig 3). Quercetin evidently enhanced fescue toxicosis-induced down-regulation of phase I, II, and II detoxification gene expression to relieve oxidative damage (Fig 4-6). Moreover, quercetin triggered the NF-kB signaling pathway to ameliorate fescue toxicosis-induced cardiovascular inflammation (Fig 7-9). Quercetin attenuated cardiac mitochondrial impaired via Parkin/PINK modulated mediated mitophagy and PGC1-α mediated biogenesis (Fig 10-13). Collectively, our findings demonstrated that quercetin explicated potential protection against fescue toxicosis-induced cardiovascular toxicity.

Integrative interactomics applied to bovine fescue toxicosis

Bovine fescue toxicosis (FT) is caused by grazing ergot alkaloid-producing endophyte (Epichloë coenophiala)-infected tall fescue. Endophyte’s effects on the animal’s microbiota and metabolism were investigated recently, but its effects in planta or on the plant–animal interactions have not been considered. We examined multi-compartment microbiota–metabolome perturbations using multi-‘omics (16S and ITS2 sequencing, plus untargeted metabolomics) in Angus steers grazing non-toxic (Max-Q) or toxic (E+) tall fescue for 28 days and in E+ plants. E+ altered the plant/animal microbiota, decreasing most ruminal fungi, with mixed effects on rumen bacteria and fecal microbiota. Metabolic perturbations occurred in all matrices, with some plant-animal overlap (e.g., Vitamin B6 metabolism). Integrative interactomics revealed unique E+ network constituents. Only E+ had ruminal solids OTUs within the network and fecal fungal OTUs in E+ had unique taxa (e.g., Anaeromyces). Three E+-unique urinary metabolites that could be potential biomarkers of FT and targeted therapeutically were identified.

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

Simple SummaryWhen endophyte-infected tall fescue is consumed by grazing livestock it can cause persistent vasoconstriction resulting in fescue toxicosis. Legumes are commonly utilized in livestock production to improve diet quality. Legumes also contain vasodilatory isoflavones that have been shown to alleviate fescue toxicosis in goats and grazing cattle. Different legumes contain varying levels and types of isoflavones. A pen study was conducted to determine if isoflavone supplementation via red clover, white clover, or soybean meal can mitigate vasoconstriction associated with fescue toxicosis in goats. Rumen fistulated Wether goats were assigned to each legume treatment at equal levels of supplementation by weight. Goats were subjected to a fescue toxicosis challenge with toxic tall fescue seed, and the carotid artery area was monitored using Doppler ultrasonography. All isoflavone treatments were able to partially mitigate vasoconstriction. Red clover, with the greatest concentration of isoflavones, was the most effective. These results demonstrate that red clover, white clover, and soybean meal supplementation can be used to reverse the vasoconstriction associated with fescue toxicosis in goats despite differences in isoflavone concentration and composition. The impact of this research is a legume-derived phytochemical that can be applied in ruminants consuming toxic tall fescue to reverse fescue toxicosis and improve animal health and productivity.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.

Dominant remodelling of cattle rumen microbiome by Schedonorus arundinaceus (tall fescue) KY-31 carrying a fungal endophyte.

Tall fescue KY-31 is an important primary forage for beef cattle. It carries a fungal endophyte that produces ergovaline, the main cause of tall fescue toxicosis that leads to major revenue loss for livestock producers. The MaxQ, an engineered cultivar, hosts an ergovaline nonproducing strain of the fungus and consequently is nontoxic. However, it is less attractive economically. It is not known how rumen microbiome processes these two forages towards nutrient generation and ergovaline transformation. We have analysed the rumen microbiome compositions of cattle that grazed MaxQ with an intervening KY-31 grazing period using the 16S rRNA-V4 element as an identifier and found that KY-31 remodelled the microbiome substantially, encompassing both cellulolytic and saccharolytic functions. The effect was not evident at the whole microbiome levels but was identified by analysing the sessile and planktonic fractions separately. A move from MaxQ to KY-31 lowered the Firmicutes abundance in the sessile fraction and increased it in planktonic part and caused an opposite effect for Bacteroidetes, although the total abundances of these dominant rumen organisms remained unchanged. The abundances of Fibrobacter , which degrades less degradable fibres, and certain cellulolytic Firmicutes such as Pseudobutyrivibrio and Butyrivibrio 2, dropped in the sessile fraction, and these losses were apparently compensated by increased occurrences of Eubacterium and specific Ruminococcaceae and Lachnospiraceae . A return to MaxQ restored the original Firmicutes and Bacteroidetes distributions. However, several KY-31 induced changes, such as the low abundance of Fibrobacter and Butyrivibrio two remained in place, and their substitutes maintained significant presence. The rumen microbiome was distinct from previously reported faecal microbiomes. In summary, KY-31 and MaxQ were digested in the cattle rumen with distinct consortia and the KY-31-specific features were dominant. The study also identified candidate ergovaline transforming bacteria. It highlighted the importance of analysing sessile and planktonic fractions separately.

Effects of overseeding red clover in endophyte-infected tall fescue pastures on steer physiology and performance

The objective of this research was to determine the effects of overseeding red clover on cattle grazing endophyte-infected tall fescue (E+ TF) pastures. A grazing study was conducted in the springs of 2016 (75 d) and 2017 (61 d). Before the start of the study, four 3-ha pastures with cool-season grass (predominately E+ TF) were blocked and randomly assigned to a control treatment (TF CON) or a broadcasted red clover treatment (TF+RC). Steers (n = 6 tester steers per pasture) were allocated to each pasture by BW. Pastures were divided into two 1.5-ha paddocks to allow for 14-d rotational put-and-take stocking. Serum prolactin was assayed on the last day of grazing, and selected tester steers from each pasture (n = 3) were moved to pens for Doppler ultrasound measurements, 7 d after grazing. Data were analyzed by repeated measures using the mixed procedure of SAS. Red clover was successfully established in TF+RC pastures (2016: 36% and 2017: 57%, pasture ground cover). The TF+RC pastures had less ADF and NDF and more true in vitro digestible DM than TF CON pastures after grazing ( P < 0.01, in all cases). However, there was no effect of TF+RC on forage mass ( P = 0.08) or pasture carrying capacity ( P = 0.19). Steers grazing TF+RC pastures had 53% and 58% greater ADG ( P = 0.03) and BW gain per hectare ( P = 0.01) than TF CON steers, respectively. Serum prolactin at the termination of grazing was almost 3 times greater in TF+RC steers than in TF CON steers ( P = 0.01). Additionally, 7 d after grazing, TF+RC steers had 44% larger caudal artery luminal areas than TF CON steers ( P < 0.01). Overseeding red clover in E+ TF pastures is an effective strategy for reversing the adverse effects of fescue toxicosis and improving cattle performance.

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

Simple SummaryThe 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.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.

Changes in Cytochrome P450 in Katahdin Ewes Fed Endophyte-infected Tall Fescue Seed Diets in Spring and Fall

Abstract Objective was to examine the activity of cytochrome P450 (CYP), a liver enzyme that metabolizes ergot alkaloids which is hindered by this fescue toxin, as an indicator of fescue toxicosis in sheep. In spring and fall, ewes were blocked by age and BW, and randomly assigned to 1 kg/ewe/d of endophyte-infected (E+; 61% of diet in fall, 13% of diet in spring; 0.8 µg/g of ergovaline; and soy hulls, alfalfa pellets, cottonseed hulls, molasses) or non-infected (E-; same proportion of E+/season and same feeds) tall fescue seed supplement (n = 10/diet in each season) for 28 d, plus hay, mineral and water. Ewes were exposed to teaser, d -21 to 0, and intact rams, d 0 (first day of diet) to 30. Rectal temperature (RT), serum concentration of prolactin (using RIA), and CYP were determined every 7–14 d between d 0–28, and pregnancy status on d 56. PromegaTM P450-Glo assay was used to determine CYP from serum. Data were analyzed by using PROC MIXED with repeated measures (SAS). Rectal temperature of E+ compared with E- ewes was elevated on at least one day in fall and spring (diet × season × d, P &amp;lt; 0.001). Serum prolactin was lower in E+ compared with E- ewes (diet × d, P &amp;lt; 0.001) and lower in fall (P &amp;lt; 0.001). CYP was higher in E- ewes on d 28 in fall (diet × season × d, P = 0.008), but otherwise similar between diets, and higher in fall than spring (P &amp;lt; 0.001). There was an unexpected negative correlation between CYP and prolactin (R = -0.24; P &amp;lt; 0.009), but there appears to be a subpopulation of ewes with low prolactin and lower CYP. CYP activity in sera may not be a marker for fescue toxicosis in ewes.

Nutritive value of fall‐stockpiled tall fescue pastures on southeastern U.S. farms

AbstractStockpiling of tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] may be a useful strategy to avoid fescue toxicosis in autumn and to reduce winter hay feeding costs of beef cattle grazing systems. Typical recommendations are to fertilize with N prior to fall growth. However, little information is available on how soil and pasture conditions affect forage nutritive value responses to fall fertilization. We analyzed the nutritive value of fall‐stockpiled forage in response to N fertilization on 92 fields in North Carolina and neighboring states from 2015 to 2018. We hypothesized that inherent soil nutrient cycling might minimize the need for exogenous N fertilizer inputs. Increasing N fertilization led to (a) greater crude protein, macronutrient concentrations (i.e., K, Ca, and P), and relative feed value and (b) lower acid detergent fiber, neutral detergent fiber, and lignin. However, changes were small, and effects were modified by surface soil properties. For example, crude protein increased from an average of 114 g kg–1 without N fertilization to 131 g kg–1 with 100 kg N ha–1, but this significant N fertilization effect diminished with increasing total organic C and inorganic N of a field. Small changes in nutritive value may have been a consequence of trials conducted on well‐managed farms with relatively high soil‐test biological activity and net N mineralization potential. Therefore, a single recommendation for fall N fertilization may not always be appropriate for enhancing nutritive value. Stockpiled tall fescue had sufficient nutritive value for pregnant cows, and N fertilization may not always be necessary.

Evaluation of Resistance to Fescue Toxicosis in Purebred Angus Cattle Utilizing Animal Performance and Cytokine Response

Fescue toxicosis is a multifaceted syndrome common in cattle grazing endophyte-infected tall fescue; however, varying symptomatic responses potentially imply genetic tolerance to the syndrome. It was hypothesized that a subpopulation of animals within a herd would develop tolerance to ergot alkaloid toxicity. Therefore, the goals of this study were to develop selection criteria to identify tolerant and susceptible animals within a herd based on animal performance, and then examine responsive phenotypic and cytokine profiles to fescue toxicosis. Angus cows grazed endophyte-infected tall fescue at two locations for 13 weeks starting in mid-April 2016. Forage measurements were collected to evaluate ergot alkaloid exposure during the study. A post hoc analysis of animal performance was utilized to designate cattle into either tolerant or susceptible groups, and weekly physiological measurements and blood samples were collected to evaluate responses to chronic exposure to endophyte-infected tall fescue. Findings from this study support the proposed fescue toxicosis selection method formulated herein, could accurately distinguish between tolerant and susceptible animals based on the performance parameters in cattle chronically exposed to ergot alkaloids, and provides evidence to warrant additional analysis to examine the impact of ergot alkaloids on immune responsiveness in cattle experiencing fescue toxicosis.

PSII-27 Effect of endophyte-infected tall fescue seed and red clover isoflavones on the serum metabolites in beef steers

Abstract Fescue toxicosis reduces animal performance, costing approximately $2 billion dollars to the beef industry annually. Emerging research has demonstrated effects of fescue toxicosis can be reduced by consumption of red clover isoflavones. The objective of the current study was to evaluate the effect of isoflavone supplementation with endophyte infected seed consumption on serum metabolites in beef steers. Angus steers (n = 36) were randomly allocated to treatments in a 2×2 factorial arrangement of endophyte-infected (E+) or endophyte-free (E-) tall fescue seed, with (P+) or without (P-) a red clover isoflavone supplement. For the 21d trial, steers were provided a basal diet supplemented with fescue seed head targeting a minimum of 0.011 mg×kg of body weight−1×d−1 of total alkaloids. A total of 943 mg isoflavones were administered daily via bolus. Following the 21d trial, blood samples were collected for metabolite analysis. Metabolites were filtered from serum and extracted using 0.1% formic acid in acetonitrile:water:methanol (2:2:1) for analysis on the Dionex UltiMate 3000 UHPLC system and Exactive Plus Orbitrap MS. The Metabolomic Analysis and Visualization Engine program was used to determine peaks and identify metabolites. Resulting metabolite data were analyzed in MetaboAnalyst 4.0 and SAS 9.4 with significance at P≤0.05. Principle component analysis indicated separation of metabolomes between E+P+ and E-P- steers. Orthogonal partial least squares discriminant analysis depicted distinct separation between P+ and P- steers and partial separation between E+ and E- steers. The variation between P+ and P- metabolomes were mainly due to differences in citrulline (r = 0.47, P = 0.003), and AMP (r = -0.35, P = 0.03) between E+ and E- metabolomes. A total of 13 and 8 metabolic pathways were impacted from differences in seed type and isoflavone treatment, respectively (P ≤ 0.05). Therefore, metabolism is altered by isoflavone supplementation that may improve animal performance during fescue toxicosis.