Use of nonergot alkaloid-producing endophytes for alleviating tall fescue toxicosis in stocker cattle

Grazing studies were conducted to determine cattle growth performance, evaluate toxicosis, and compare grazing behavior in stocker cattle grazing nonergot alkaloid-producing endophyte-infected (AR542 or AR502), endophyte-free (E-), or wild-type toxic endophyte-infected (E+) Jesup, Georgia-5, and Kentucky-31 tall fescue. Replicated 0.81-ha tall fescue paddocks were established at the Central Georgia Branch Station at Eatonton and the Northwest Georgia Branch Station at Calhoun during October 1998 and were stocked with beef cattle for autumn and spring periods from fall 1999 through spring 2002. Mean ergot alkaloid concentrations were higher (P < 0.01) on E+ pastures than the other treatments at both locations. At Calhoun and Eatonton, post-treatment serum prolactin concentrations were decreased (P < 0.01) on E+ compared with AR542, AR502, and E- tall fescue. Cattle on AR542, AR502, and E- pastures had lower (P < 0.05) post-treatment rectal temperatures than cattle grazing E+ tall fescue during spring at Eatonton and Calhoun. Calf ADG was higher (P < 0.05) on AR542, AR502, and E- as compared with E+ tall fescue during autumn and spring grazing at Eatonton, and at Calhoun, cattle on E+ pastures had lower (P < 0.05) ADG in both autumn and spring. Gain/hectare was higher (P < 0.05) on AR542, AR502, and E- than on E+ during autumn at Eatonton and during spring at both locations. In autumn at Calhoun, gain/hectare was greater (P < 0.05) on AR502 and E- compared with E+ tall fescue. During April, May, and June, cattle grazing E+ pastures at Eatonton spent more (P < 0.01) time idling, more (P < 0.01) time standing, and used more (P < 0.01) water than cattle on AR542 and E- tall fescue. Daily prehensions and biting rate were each higher (P < 0.01) on AR542 and E- tall fescue than E+ tall fescue in both grazing seasons. There were no differences among pasture treatments for bite size in either spring (P = 0.50) or autumn (P = 0.34). Steers grazing E+ pastures had lower DMI than steers grazing AR542 and E- pastures during spring (P < 0.10) and lower DMI than steers grazing E- pastures during autumn (P < 0.05). Daily steer water usage was decreased (P < 0.10) in E+ pastures compared with AR542 and E- pastures during late fall. These results indicate that nonergot alkaloid-producing endophyte technology is a promising option for alleviating tall fescue toxicosis in stocker cattle.     

Productivity of cow-calf pairs grazing tall fescue pastures infected with either the wild-type endophyte or a nonergot alkaloid-producing endophyte strain, AR542

The nonergot alkaloid-producing endo-phyte, AR542, has been shown to improve the persistence and yield of tall fescue pastures without causing the animal disorders commonly associated with tall fescue toxicosis. A 3-yr grazing study was conducted to compare effects of AR542-infected tall fescue pastures with wild type endophyte-infected (E+) tall fescue pastures on cow-calf performance. Replicated 7.3-ha pastures of each treatment were grazed by cow-calf pairs (16 pairs per pasture replication) each year from March to weaning in September. The cows were exposed to breeding on their respective pasture treatments from April 1 through June 15. The treatment groups were compared for reproductive performance, ADG, BCS, calf growth rate, and weaning weight. Blood samples were also collected for serum prolactin (PRL) analysis. There were no significant differences in calving rate (P = 0.98) or calving interval (P = 0.62) between pasture treatments. Cows that grazed the AR542 pastures subsequently gave birth to calves that were heavier (P < 0.05) than calves from cows that had grazed the E+ pastures. Cows grazing the AR542 pastures had higher (P < 0.05) BCS at the end of the grazing period, and had higher ADG during the grazing period. Calves raised on the AR542 pasture had higher (P < 0.05) ADG and weaning weights than calves of the same sex raised on the E+ pastures. Serum PRL concentrations were decreased (P < 0.05) in both cows and calves on the E+ pastures compared with serum PRL concentrations in cows and calves grazing the AR542 pastures. The results indicate that grazing tall fescue pastures infected with the AR542 endophyte may give significant advantages in cow-calf growth rates and BCS over grazing E+ pastures. However, there did not seem to be any benefit in reproductive performance in this trial. There was a small, but significant increase in birth weight in cows grazing AR542 pasture.     

Effects of feeding ergovaline on lamb performance in a heat stress environment

Lambs exposed to a heat-stressed environment (33 degrees C, 50% relative humidity) were used in three experiments to determine whether ergovaline (EV) is the primary toxin involved in fescue toxicosis. The first study evaluated the effects of feeding diets containing increasing levels of endophyte-infected tall fescue seed (E+) and decreasing levels of endophyte-free tall fescue seed (E-). The second and third study evaluated the response to a diet that contained synthetic EV added to an E- diet and the response to a diet containing endophyte-infected ryegrass seed (R+) with an elevated concentration of EV. In Exp. 1, lambs were fed diets of: 1) 10% E- and 0% E+, 2) 5% E- and 5% E+, or 3) 0% E- and 10% E+. Increasing the percentage of E+ in the diet resulted in a linear decrease (P < 0.01) in feed intake (as-fed basis), skin temperature, thermocirculation index (TCI), and serum prolactin. Body weight gain also decreased (P < 0.06). Respiratory rate and core body temperature were not affected by the 5 or 10% E+ diets. In Exp. 2, lambs were fed diets that contained: 1) 10% E-, 2) 10% E- with synthetic EV added at a level equivalent to the 10% E+ diet, or 3) 10% E+. Feed intake (as-fed basis), body weight gain, and skin temperature did not differ for lambs fed the E- and EV diets. The EV diet elicited a decrease (P < 0.05) in TCI and prolactin compared with the E- diet. The TCI for lambs fed EV did not differ (P > 0.10) from the E+ lambs; however, serum prolactin was lower (P < 0.05) for lambs on the E+ diet than for those fed EV. Core body temperature was not affected (P > 0.10) by feeding EV or E+ fescue seed in Exp. 2. In Exp. 3, lambs were fed diets that contained: 1) 10% E-, 2) 3.24% R+ and 6.76% E-, which added an equivalent amount of EV to E+ diets but reduced concentrations of other ergot alkaloids, or 3) 10% E+. Lambs fed the E+ diet and maintained at 33 degrees C had lowered feed intake (as-fed basis), skin temperature, and TCI compared with lambs fed the E- or R+ diets (P < 0.05). Lambs fed the E+ diet had increased rectal temperatures and lowered serum prolactin compared with lambs on the R+ diet (P < 0.05). Lambs on the R+ diet had a greater rectal temperature and lower serum prolactin than lambs on the E- diet (P < 0.05). These results suggest that EV is a fescue toxin; however, other alkaloids might work synergistically with EV, causing the full expression of fescue toxicosis.     

Urinary alkaloid excretion as a diagnostic tool for fescue toxicosis in cattle.

Fescue toxicosis research studies have often included serum prolactin as a physiologic index of the disorder. Serum prolactin has not been used as a clinical measure of fescue toxicosis because of variation associated with sex and physiologic condition of the animal and climatic and seasonal factors. The primary excretory route of the alkaloids responsible for this toxicosis is the urine. Three pasture experiments were conducted to examine serum prolactin and urinary ergot alkaloid variability among steers continuously grazing endophyte-infected (E+) or endophyte-free (E-) tall fescue and among steers that were switched from one pasture form to the other. A fourth grazing experiment was used to examine how to best to manage the steers prior to sampling for urinary ergot alkaloid excretion. Coefficients of variability for urinary alkaloid excretion were consistently lower (46-65%) than serum prolactin (64-142%). Urinary alkaloid excretion patterns changed within 12 hours following switching steers from E+ to E- pasture or vice versa, but serum prolactin was recalcitrant to change. Because it is less variable and more dynamic than serum prolactin, urinary alkaloid excretion can be used for health assessment of steers grazing E+ and E- pastures. Regression analysis established a quadratic relationship between alkaloid excretion and average daily weight gain, with a regression coefficient of 0.86. Urinary alkaloid analysis was useful in determining whether cattle were consuming toxic tall fescue.     

Growth rate and physiology of steers grazing tall fescue inoculated with novel endophytes

Cattle grazing tall fescue (Festuca arundinacea Schreb.) often develop fescue toxicosis. This condition is thought to be caused by ergot alkaloids produced by the endophyte Neotyphodium coenophialum. Endophytes from wild tall fescue plants, which do not produce ergot alkaloids, were transferred into the endophyte-free tall fescue germplasm, HiMag. The novel associations also lacked the ability to produce ergot alkaloids. Our objective was to determine whether cattle grazing these novel endophyte associations showed signs of fescue toxicosis. At the Fayetteville, Arkansas location, tester steers (n = 72) were assigned to one of four pasture treatments: endophyte-free HiMag tall fescue (HiMag-); 'Kentucky-31' tall fescue infected with its native, toxic endophyte (KY+); and two novel endophyte-infected tall fescue associations, HiMag4 and HiMag9. At the Mount Vernon, Missouri location, steers (n = 54) were used to test three of the four cultivars (HiMag9 was not tested). Ergot alkaloid concentrations in the forage of HiMag4 and HiMag9 were low or undetectable. Respiration rate, rectal temperature, ADG, and hair scores were measured during the grazing period. Blood was collected via jugular venipuncture and used for prolactin, aspartate aminotransferase, alkaline phosphatase (ALP), lactate dehydrogenase (LDH), cholesterol, triglyceride, and creatinine analysis. Weight gains by steers grazing HiMag4 and HiMag9 did not differ from those of steers grazing HiMag-, but were greater than gains (P < 0.05) by steers on the KY+ treatment. Steers grazing KY+ had higher (P < 0.05) respiration rates, rectal temperatures, and hair scores than did steers grazing novel endophyte and HiMag- pastures. Prolactin, ALP, cholesterol, LDH, and triglycerides all were suppressed (P < 0.05) in steers grazing KY+ compared with steers grazing novel endophyte and HiMag- pastures. Steers grazing the novel endophyte tall fescues did not suffer from the decreased weight gains and toxicities associated with fescue toxicosis, resulting in enhanced animal production.     

Effects of short-term early gestational exposure to endophyte-infected tall fescue diets on plasma 3,4-dihydroxyphenyl acetic acid and fetal development in mares

Consumption of wild-type (toxic) endophyte-infected tall fescue (E+) by horses during late gestation is known to adversely affect pregnancy outcome; however, little is known of the potential disruptive consequences of E+ consumption by mares during the critical phases of placentation and fetal development in early pregnancy. The objective of this study was to evaluate the detrimental effects of feeding E+ to mares during early gestation. Mares (n = 12) paired by stage of gestation (d 65 to 100) were assigned to diets (six per diet) consisting of endophyte-free (E-) or E+ tall fescue seed (50% E- or E+ tall fescue seed, 45% sweet feed, and 10% molasses fed at 1.0% of BW/d). Mares also had ad libitum access to E+ or E- annual ryegrass hay, and were fed diets for 10 d. Following removal from the tall fescue diet on d 11, mares were placed on common bermudagrass pasture and monitored until d 21. Morning and evening rectal temperatures were recorded and daily blood samples were collected for progesterone and prolactin (PRL) analyses, whereas samples for 3,4-dihydroxyphenyl acetic acid (a catecholamine metabolite) analysis were collected on alternate days. For clinical chemistry analysis, blood samples were collected on d 0, 5, 10 and 21. Daily urine samples were collected for ergot alkaloid analysis, and ultrasonography was performed for presence of echogenic material in fetal fluids. Rectal temperatures (E+ 37.76+/-0.03; E- 37.84+/-0.03 degrees C) and serum PRL concentrations (E+ 14.06< or =0.76; E- 12.11+/-0.76 ng/mL) did not differ (P = 0.96) between treatments. Measuring the change in basal serum concentration from d 0 over time, progesterone concentrations did not differ (-0.64 +/-1.49 and -0.55+/-1.47 ng/mL for E+ and E- mares, respectively). There was no negative pregnancy outcome, and ultrasonography indicated no increase in echogenic material in fetal fluids. Plasma 3,4-dihydroxyphenyl acetic acid concentrations decreased (P < 0.05) in E+ compared with E- mares (2.1+/-0.14 and 4.4+/0.43 ng/mL, respectively). Urinary ergot alkaloid concentration was greater (P < 0.01) in mares consuming E+ compared with E- (532.12+/- 52.51 and 13.36+/-2.67 ng/mg of creatinine, respectively). Although no fetal loss was observed during the current study, elevated concentrations of urinary ergot alkaloid were consistent with depressed endogenous catecholamine activity, suggestive of an endocrine disruptive effect of hypothalamic origin.     

Effect of endophyte type on carcass traits, meat quality, and fatty acid composition of beef cattle grazing tall fescue

Fourteen Hereford steers were used to compare carcass traits, meat quality, and fatty acid composition of beef from cattle grazing tall fescue infected with either wild-type (E+; n = 6) or novel, nil ergot alkaloid (AR542; n = 8) endophyte for 209 d. Average daily gain, live weight, and HCW were greater (P < 0.05) for AR542 cattle than for E+. No differences in LM color or pH were observed between AR542 and E+. Steaks from E+ cattle tended (P = 0.10) to have higher L* and b* than those from AR542 cattle at 0 d of display. Ground beef from E+ cattle also had higher (P < 0.05) L* than AR542 cattle, with no differences in a* or b* at 0 d of display. Color changes during display did not differ for both steaks and ground beef from E+ and AR542. Lipid oxidation levels increased (P < 0.05) during simulated retail display, but they did not differ between endophyte treatments. Adipose tissues from E+ cattle had a higher (P < 0.05) percentage of SFA, and a lower (P < 0.05) percentage of MUFA than adipose from AR542 cattle. Ground beef and i.m. fat had higher (P < 0.05) concentrations of SFA, MUFA, and cis-9, trans-11 isomer of conjugated linoleic acid, and lower (P < 0.05) concentrations of PUFA and PUFA:SFA ratio than s.c. fat. The n-6:n-3 fatty acid ratio did not differ among fat depots. Ergot-alkaloids were detected in s.c. adipose tissues, and alkaloid concentration was greater (P < 0.05) for E+ than AR542. Warner-Bratzler shear force values did not differ between endophyte types, but it decreased (P < 0.01) across the postmortem aging period. Conversely, sensory panel evaluation detected greater (P < 0.01) chewiness and lower (P < 0.05) juiciness for AR542 than for E+ steaks aged for 14 d. Although grazing cattle on tall fescue pastures infected with nil ergot alkaloid endophyte improved cattle performance, these results suggest that endophyte type has minor effects on carcass traits and meat quality of pasture-fed beef. Moreover, finishing cattle on tall fescue pastures showed the potential to enhance the fatty acid profile of beef from a human health perspective. Alkaloid concentration was greater (P < 0.05) in s.c. fat from E+ than AR542 (2.81 vs. 0.92 ppb; fresh-tissue basis). This is the first published report demonstrating the presence of alkaloids in beef tissues.     

Evaluation of a ruminally dosed tall fescue seed extract as a model for fescue toxicosis in steers

Tall fescue (Lolium arundinaceum) toxicosis research is often complicated by a reduction in intake of infected forage or seed, making treatment comparisons difficult. This study was conducted to develop a fescue toxicosis model that would allow for variations in DMI without altering the quantity of alkaloids consumed over the course of the experiment. Ground tall fescue seed and a tall fescue seed extract were used in two 2-period crossover experiments to determine the effectiveness of ruminal dosing of a tall fescue seed extract to induce fescue toxicosis. This experiment used 4 growing Holstein steers (BW = 337 ± 24 kg) surgically fitted with ruminal cannulas. Steers were maintained on a diet of endophyte-free fescue hay fed ad libitum throughout the experiment. Endophyte-infected (E+; 4.1 mg/kg of ergovaline) and uninfected (E-; 0.0 mg/kg of ergovaline) KY-31 tall fescue seed was ground and dosed or extracted with ethanol, concentrated, and lyophilized before ruminal dosing. Ergovaline concentration of the final extract was 102 mg/kg. Animals were given a minimum of a 3-wk washout period between treatments. Physiological indicators were measured over 7 d at 22°C (d 1 to 3) and 32°C (d 4 to 7) during both seed and extract dosing. Seed and extract E+ dosing reduced serum prolactin concentrations such that they were not different from zero (P < 0.10). Treatment with E+ reduced feed intake (P < 0.05) and heart rate (P < 0.001), and increased respiration rate (P < 0.01) and core temperature (P < 0.05) during both seed and extract dosing. Increasing environmental temperature from 22 to 32°C reduced total intake (P < 0.05) and increased core temperature (P < 0.001) and respiration rate (P < 0.001) during both seed and extract dosing. Diastolic blood pressure tended (P < 0.09) to be increased during E+ extract dosing and reduced during heat stress. These physiological alterations are consistent with those reported for cattle grazing or consuming seed from endophyte-infected tall fescue. These data indicate that a ruminally dosed ethanol extract of tall fescue seed is efficacious in inducing fescue toxicosis in cattle.     

Animal performance and economic comparison of novel and toxic endophyte tall fescues to cool-season annuals

Increased costs of annual establishment of small grain pasture associated with fuel, machinery, and labor are eroding the profitability of stocker cattle enterprises. Interest has therefore increased in development of cool-season perennial grasses that are persistent and high quality. This study occurred on 24 ha (divided into thirty 0.81-ha paddocks) located at the University of Arkansas Division of Agriculture Livestock and Forestry Branch Station, near Batesville. Two tall fescue (Festuca arundinacea Schreb.) cultivars infected with novel endophytes (NE), Jesup infected with AR542 endophyte (Jesup AR542), and HiMag infected with Number 11 endophyte (HM11) were established in September 2002. Jesup AR542 and HM11 were compared with endemic endophyte Kentucky 31 (KY-31) tall fescue; wheat (Triticum aestivum L.) and cereal rye (WR, Secale cereale L.) planted in September 2003, 2004, and 2005; and annual ryegrass [RG, Lolium perenne L. ssp. multiflorum (Lam.) Husnot] planted in September 2004 and 2005. Each year, 3 steers (3.7 steers/ha) were placed on each pasture for fall and winter grazing, and 5 steers (6.2 steers/ha) were placed on each pasture for spring grazing. Animal performance is presented by year in the presence of a year x treatment interaction (P < 0.01). Body weight gain per hectare of steers grazing NE tall fescue was greater (P < 0.01) than those of KY-31 and WR during 2003 to 2004, whereas in 2004 to 2005, BW gain per hectare of steers grazing NE and RG did not differ (P < or = 0.29) and was greater (P < 0.01) than that of WR, which was greater (P < 0.01) than that of KY-31. During 2005 to 2006, BW gain per hectare was greater (P < 0.01) for steers grazing RG than those of NE and WR, which did not differ (P > or = 0.14). Body weight gain per hectare was least (P < 0.01) for steers grazing KY-31. Average net return of NE tall fescue was greater (P < 0.01) than KY-31, but profitability of NE did not consistently differ from cool-season annuals. Across the 3-yr study, NE tall fescue produced net returns per hectare of $219; this level of profitability would require 4 yr for a new planting of NE tall fescue to break even. Novel endophyte tall fescues offer potential benefits related to decreased risk of stand establishment of annual forage crops, longer growing season, and acceptable animal performance.     

Influence of endophyte-infected tall fescue on serum prolactin and progesterone in gravid mares.

Thirty mares in late gestation were used in a 3-yr study to assess effects of the tall fescue endophyte Acremonium coenophialum on serum prolactin (PRL) and progesterone. Two paddocks of each treatment, 0 or 100% infected 'Kentucky 31' tall fescue, were grazed by the mares for 21 d. Blood was collected three times per week until parturition. At 7-d intervals, mares were challenged with thyrotropin-releasing hormone (TRH) while grazing and blood was collected postinjection. Mares grazing 100% infected tall fescue (E+) had decreased serum PRL compared with mares grazing the 0% infected tall fescue (E-) in 2 of 3 yr. Within 8 d postgrazing, serum PRL for E+ mares equaled or surpassed values of the E- mares. Serum PRL was not different during the 3rd yr. In response to TRH, serum PRL rate of increase was similar between treatments but remained elevated (P less than .01) in the E+ mares at the 180-, 240-, and 300-min sample times. Serum progesterone was lowered (P less than .05) by E+ but increased to control values within 10 d postgrazing. It is concluded that serum PRL and progesterone in the gravid mare were decreased by the presence of A. coenophialum in 'Kentucky 31' tall fescue grass but normal levels were reestablished within 2 to 3 wk.     

Alterations in hemograms and serum biochemical analytes of steers after prolonged consumption of endophyte-infected tall fescue

The objective of the current study was to delineate changes that occur in serum analytes and blood cellular elements in cattle that graze endophyte-infested (Neotyphodium coenophialum) tall fescue. Tall fescue is grown on more than 35 million acres (14.2 million ha) of pasture in the United States, and three-fourths of the pastures are infected with the endophyte at a 60% or greater level. Tall fescue toxicosis caused by endophyte-produced ergot alkaloids continues to be the most important grass-related disease in the United States, in terms of economic loss to animal producers. However, the agronomic attributes of tall fescue make it an attractive forage species because of its ability to withstand cool temperatures, drought, poor soil conditions, and intensive defoliation from herbivore species, including insects. Tall fescue toxicosis is a complex disease and the need exists to understand the mechanisms of the toxic effects in order to institute effective, prophylactic control measures. Our group previously reported changes that occur in serum biochemical analytes of cattle that graze endophyte-infected tall fescue. An additional year's worth of data have been added, strengthening and corroborating these data. Consistent and significant changes associated with tall fescue toxicosis during the 3-yr study included decreased serum concentrations of cholesterol, globulin (increased albumin/globulin ratio), prolactin, total protein, and copper. The activity of alanine aminotransferase was decreased in serum, whereas an increase in serum concentrations of creatinine and total bilirubin occurred. The present report also documents comparative hemograms of cattle that grazed endophyte-infected or endophyte-free tall fescue over a prolonged period. The mean erythrocyte counts were increased in cattle that grazed endophyte-infected tall fescue, whereas mean corpuscular hemoglobin and mean corpuscular volume were decreased, as were mean eosinophil counts. Thus, repeatable changes have been identified that occur in serum biochemical and blood cellular values of cattle grazing endophyte-infected tall fescue that will aid in understanding the pathogenesis of the disease. In addition, these consistently altered parameters can be used to assess the effectiveness of potential prophylactic treatments.     

Effects of hydrated sodium calcium aluminosilicate on fescue toxicosis and mineral absorption.

The possibility of supplementing livestock diets with an aluminosilicate to protect them from fescue toxicosis was investigated. An in vitro study showed that hydrated sodium calcium aluminosilicate (HSCAS) removed greater than 90% of the ergotamine from aqueous solutions at pH 7.8 or lower, indicating a high affinity of ergotamine for HSCAS in vitro. Rats fed diets containing tall fescue seed infested (E+) with the endophytic fungus Acremonium coenophialum had lower (P less than .05) feed intakes and weight gains than did rats fed diets containing uninfested (E-) tall fescue seed. When feed intake by rats fed the E- seed diet was limited to that of rats fed the E+ seed diet, weight gains did not differ, but testes weights and serum prolactin (PRL) concentrations were lower (P less than .05 and .10, respectively) in rats receiving E+ seed. Supplementing E+ seed diets with HSCAS did not eliminate effects of E+ seed on intake, PRL, or testes weights. Sheep fed E+ tall fescue hay had higher (P less than .05) rectal temperatures than did sheep fed an equal amount of E- tall fescue hay, but OM and N digestion coefficients did not differ between the two hays. Supplementing E+ hay diets with HSCAS did not eliminate the effect of E+ hay on rectal temperatures. Addition of 2% HSCAS to tall fescue hay diets did not affect apparent absorption by sheep of OM, N, Ca, P, Na, K, or Cu, but it reduced (P less than .05) the apparent absorption of Mg, Mn, and Zn.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thiamin supplementation and the ingestive behavior of beef cattle grazing endophyte-infected tall fescue

Livestock grazing endophyte (Acremonium coenophialum Morgan-Jones and Gams)-infected tall fescue (Festuca arundinacea Schreb.) perform poorly due to tall fescue toxicosis, especially when animals are under heat stress. In order to determine whether thiamin promotes recovery from tall fescue toxicosis, 1 or 0 g of thiamin per day, as mononitrate, was fed orally to adult Angus (Bos taurus) cows (380 +/- 8 kg) grazing either tall fescue pasture with and without endophyte or alfalfa (Medicago sativa L.). A tethered grazing system employing a split-plot design was used to estimate intake and components of ingestive behavior. No significant differences attributable to thiamin supplements were seen in rates of intake and biting, grazing time and intake per bite when cows grazed endophyte-infected tall fescue during the first 4 d of exposure. When cows grazed endophyte-infected (greater than 95%) tall fescue with 2,091 micrograms/g loline alkaloids after 4 d of exposure, the untreated animals ingested herbage dry matter (DM) at 1.19 kg/h, whereas the cows receiving thiamin ate 1.57 kg/h (P less than .05). Cattle achieved these rates of DM intake by forming bites of 1.0 and 1.2 g DM at 24 and 26 bites/min when treated with 0 and 1 g of thiamin per day, respectively. Thiamin supplements had no effect on ingestive behavior of cows grazing endophyte-free tall fescue or alfalfa after exposure to these forages for 4 d. Responses to thiamin generally were greater when cattle grazing endophyte-infected tall fescue were exposed to heat stress. Oral thiamin supplementation may alleviate tall fescue toxicosis of beef cattle during warm weather.     

Effects of initial and extended exposure to an endophyte-infected tall fescue seed diet on faecal and urinary excretion of ergovaline and lysergic acid in mature geldings

AIM: To determine the amount of ergovaline and lysergic acid retained or excreted by geldings fed endophyte-infected seed containing known concentrations of these alkaloids, and the effects of exposure time on clinical expression of toxicosis. METHODS: Mature geldings (n=10) received diets containing either endophyte-free (E-) or endophyte-infected (E+) tall fescue seed during three experimental phases. The first phase (Days -14 to -1) was an adaptation phase, to allow all horses to adapt to a diet containing E- tall fescue seed. The second (Days 0 to 3) was the initial exposure phase to E+ tall fescue seed, used for the delivery of ergovaline and lysergic acid at 0.5 and 0.3 mg/kg of diet, respectively, to test the initial effects of exposure on routes and amounts of elimination of alkaloid. During this phase, half the geldings were exposed to an E+ diet while the rest served as controls by remaining on the E- diet. Once assigned to treatments, geldings remained on the same diet through the third phase (Days 4 to 21), which served as the extended exposure phase. Total outputs of faeces and urine were collected within each phase, to determine retention of ergovaline and lysergic acid and nutrient digestibility. Serum was collected weekly and analysed for activities of enzymes and concentrations of prolactin. Bodyweights (BW) and rectal temperatures were recorded weekly. RESULTS: BW, rectal temperature, enzyme activities and concentrations of prolactin in serum, and nutrient digestibility were not affected by treatment. Total intake of ergovaline by geldings on the E+ diet was 3.5 and 3.6 (SE 0.20) mg/day, and 2.1 and 2.3 (SE 0.11) mg/day were not accounted for in initial and extended phases, respectively. Lysergic acid was excreted in the urine (4.0 and 4.9 (SE 0.97) mg/day) and faeces (2.5 and 2.7 (SE 0.35) mg/day) at greater amounts than that consumed (2.0 and 1.9 (SE 0.09) mg/day) during the initial and extended exposure phases, respectively. Animals exposed to E+ seed for a period of 20 days appeared to excrete more (1.5 vs 1.2 mg/day; SE 0.08; p=0.03) ergovaline in the faeces than those exposed for only 4 days. CONCLUSIONS: Exposure time to the ergot alkaloids had a limited effect on the route of elimination or the amounts of ergovaline or lysergic acid excreted by horses. The primary alkaloid excreted was lysergic acid, and urine was the major route of elimination. These data will aid future research to improve animals' tolerance to toxic endophyte-infected tall fescue.     

A model of fescue toxicosis: responses of rats to intake of endophyte-infected tall fescue

A study was conducted to develop a model for fescue toxicosis using rats fed a diet containing endophyte-infected tall fescue seed (E+). Rats implanted with telemetric transmitters to continuously monitor core body temperature (Tc) and activity were housed at thermoneutrality (21 degrees C) and were fed a diet containing endophyte-free fescue seed (E-). After 2 wk, they were assigned to either E+ or E- diets and initially maintained at thermoneutrality (preheat) for 8 d. They were then exposed to heat stress (31 degrees C) for 22 d, followed by 1 wk of recovery at thermoneutrality (post-heat). Body weight and feed intake were measured daily. Rats receiving the E+ diet showed decreased feed intake (P = 0.001) and weight gains (P = 0.003) during the preheat period. The decrease in Tc from the pre-treatment level was greater in E+ than in E- rats during the preheat (P = 0.001) and postheat (P = 0.001) periods. With heat stress, both groups showed parallel decreases in feed intake. The increase in Tc from pre-heat to heat conditions was greater in E+ vs. E- rats (P = 0.001). Activity level was lower in E+ than in E-rats during heat stress (P = 0.009) and postheat (P = 0.037) periods. These results show that the rat model for fescue toxicosis is extremely useful because many of the observed responses to E+ diet are similar to those noted for cattle, and additional variables that are difficult to measure in cattle, such as activity, can be easily evaluated.     

Induction of tall fescue toxicosis in heat-stressed cattle and its alleviation with thiamin

Livestock grazing endophyte (Acremonium coenophialum)-infected tall fescue (Festuca arundinacea Schreb. cv. Kentucky 31) at high ambient temperatures may suffer from fescue toxicosis. Adult Angus cows (Bos taurus) were fed 0 to 1 kg/d of 70% infected tall fescue seed containing about 4.4 g of loline alkaloids in factorial combination with thiamin at 0 or 1 g/d. Cows assigned to the zero level of tall fescue seed received a supplement of equivalent energy and protein. Ingestive behavior was measured at 1330 to 1430 EDT during two 4-d periods in two consecutive weeks in August on alfalfa (Medicago sativa L.) pastures using a tethered grazing system. Alfalfa intake per measured grazing session of cows given tall fescue seed declined linearly (P less than .01) as air temperatures during grazing increased above 25 degrees C, largely because of shorter grazing meals. Thiamin increased alfalfa intake per measured grazing session by extending grazing time. Alkaloids in ingested endophyte-infected tall fescue induce thiamin deficiencies in cattle that result in symptoms of tall fescue toxicosis.     

Effects of initial and extended exposure to an endophyte-infected tall fescue seed diet on faecal and urinary excretion of ergovaline and lysergic acid in mature geldings

Abstract

AIM: To determine the amount of ergovaline and lysergic acid retained or excreted by geldings fed endophyte-infected seed containing known concentrations of these alkaloids, and the effects of exposure time on clinical expression of toxicosis.

METHODS: Mature geldings (n=10) received diets containing either endophyte-free (E-) or endophyte-infected (E+) tall fescue seed during three experimental phases. The first phase (Days ?14 to ?1) was an adaptation phase, to allow all horses to adapt to a diet containing E- tall fescue seed. The second (Days 0 to 3) was the initial exposure phase to E+ tall fescue seed, used for the delivery of ergovaline and lysergic acid at 0.5 and 0.3 mg/kg of diet, respectively, to test the initial effects of exposure on routes and amounts of elimination of alkaloid. During this phase, half the geldings were exposed to an E+ diet while the rest served as controls by remaining on the E- diet. Once assigned to treatments, geldings remained on the same diet through the third phase (Days 4 to 21), which served as the extended exposure phase. Total outputs of faeces and urine were collected within each phase, to determine retention of ergovaline and lysergic acid and nutrient digestibility. Serum was collected weekly and analysed for activities of enzymes and concentrations of prolactin. Bodyweights (BW) and rectal temperatures were recorded weekly.

RESULTS: BW, rectal temperature, enzyme activities and concentrations of prolactin in serum, and nutrient digestibility were not affected by treatment. Total intake of ergovaline by geldings on the E+ diet was 3.5 and 3.6 (SE 0.20) mg/day, and 2.1 and 2.3 (SE 0.11) mg/day were not accounted for in initial and extended phases, respectively. Lysergic acid was excreted in the urine (4.0 and 4.9 (SE 0.97) mg/day) and faeces (2.5 and 2.7 (SE 0.35) mg/day) at greater amounts than that consumed (2.0 and 1.9 (SE 0.09) mg/day) during the initial and extended exposure phases, respectively. Animals exposed to E+ seed for a period of 20 days appeared to excrete more (1.5 vs 1.2 mg/day; SE 0.08; p=0.03) ergovaline in the faeces than those exposed for only 4 days.

CONCLUSIONS: Exposure time to the ergot alkaloids had a limited effect on the route of elimination or the amounts of ergovaline or lysergic acid excreted by horses. The primary alkaloid excreted was lysergic acid, and urine was the major route of elimination. These data will aid future research to improve animals′ tolerance to toxic endophyte-infected tall fescue.     

Integrating bermudagrass into tall fescue-based pasture systems for stocker cattle

The daily BW gain of stocker steers grazing tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbysh. = Schedonorus arundinaceus (Schreb.) Dumort.]-based pastures typically declines during summer. To avoid these declines, in part to mitigate the effects of tall fescue toxicosis, it is commonly advised to move cattle to warm-season forage during this period. A 3-yr (2006, 2007, and 2008) grazing study was conducted to evaluate the effect of replacing 25% of the area of a tall fescue/clover (81% endophyte-infected) pasture system with "Ozark" bermudagrass [Cynodon dactylon (L.) Pers.] overseeded with clover (Trifolium spp.) to provide summer grazing for stocker steers (TF+BERM). The TF+BERM treatment was compared with a grazing system in which tall fescue/clover (TF) pastures were the only type of forage available for grazing. Our objective was to determine if replacement of 25% of the land area in a fescue system with bermudagrass would increase annual beef production compared with a system based solely on tall fescue. The study was conducted at the Southwest Research and Education Center of the University of Missouri near Mt. Vernon. Each treatment was rotationally stocked with 5 steers (248 ± 19.3 kg) on 1.7 ha. Fertilizer applications were applied at rates recommended for each respective forage species. Total forage production, BW gain per hectare, and season-long ADG of steers was greater (P < 0.06) for TF+BERM than for TF in 2006, but none of these measures differed (P > 0.19) in 2007 or 2008. In vitro true digestibility of pastures was greater (P = 0.01) for TF (84.4%, SEM = 0.64%) compared with TF+BERM (80.6%, SEM = 0.79%), even in summer. The decreased in vitro true digestibility of the bermudagrass pastures likely negated any benefit that animals in TF+BERM had in avoiding the ergot-like alkaloids associated with endophyte-infected tall fescue. Renovating 25% of the pasture system to bermudagrass provided some benefit to the system in years when summertime precipitation was limited (2006) but provided no value in wetter years (2007 and 2008). Although renovating endophyte-infected tall fescue pastures to a warm-season forage is a widely used practice to mitigate tall fescue toxicosis, the benefits of this practice are limited if forage quality of the warm season component is poor.     

Influence of protein supplementation and implant status on alleviating fescue toxicosis

Heat stress is a major problem in transporting stocker calves with symptoms of fescue toxicosis. Removing calves from tall fescue pastures and offering diets devoid of endophyte-infected tall fescue could reduce the severity of toxicosis and precondition calves for transport to the feedlot. In the present experiment, a pasture phase was used to condition yearling steers to grazing tall fescue and induce symptoms of fescue toxicosis, and a pen phase followed to determine effects of implanting at the start of grazing and protein supplementation (hay only vs hay plus supplement) on short-term changes in rectal temperature and serum prolactin concentration. Neither implant status nor protein supplementation affected (P > 0.10) white blood cell count or rectal temperature. White blood cell counts at the conclusion of the pasture phase averaged 8,778 cells/microL and were within a range indicating no immunological response. Changes in rectal temperature and serum prolactin concentration during the pen phase were not influenced (P > 0.10) by implanting or supplementation. Initial rectal temperatures for the pen phase were high (39.9 degrees C) but declined linearly (P < 0.001) over the first 106 h and were below a normal temperature (39.2 degrees C) by 82 h following removal from tall fescue pastures. Serum prolactin gradually increased (P < 0.001) to a peak by 82 h and stabilized thereafter. Results indicate that neither supplemental protein nor an estrogenic implant influenced recovery indices of fescue toxicosis, whereas removing calves from tall fescue pastures and excluding dietary tall fescue for 3 to 4 d may alleviate symptoms of fescue toxicosis.     

Effect of fescue toxicosis on hepatic gene expression in mice

Fescue toxicosis affects wild and domestic animals grazing fescue pasture infected with the endophytic fungus Neotyphodium coenophialum. Signs of fescue toxicosis include increased core body temperature and respiration rate and decreased milk yield and reproductive performance. Laboratory mice also exhibit symptoms of fescue toxicosis, as indicated by reduced growth rate and reproductive performance. Mice were used to study the effects of fescue toxicosis on hepatic gene expression. Twenty-seven mice were randomly allocated to a diet containing either 50% endophyte-infected (E+; 6 ppm ergovaline) or endophyte-free (E-) fescue seed for 2 wk under thermoneutral conditions. Liver genes differentially expressed due to fescue toxicosis were identified using DNA microarray. A 2-stage ANOVA of microarray data identified 36 differentially expressed genes between mice fed E+ and E- diets. Another analysis method, significance analysis of microarray, identified 9 genes as differentially expressed between treatment groups, and some genes overlapped with genes identified by ANOVA. Hierarchical clustering of 36 genes identified by ANOVA clearly separated the mice by diet, with 100% confidence as computed by bootstrap analysis. Expression of 11 genes was verified using quantitative real-time PCR. The E+ diet resulted in downregulation of genes involved in the sex-steroid metabolism pathway and genes involved in cholesterol and lipid metabolism. Genes coding for ribosomes and protein synthesis were upregulated by the E+ diet. Genes identified in the present analysis indicate some of the mechanisms by which fescue toxicosis occurs in animals.