Hemodynamic responses of the caudal artery to toxic tall fescue in beef heifers

Color Doppler ultrasonography was used to compare blood flow characteristics in the caudal artery of heifers fed diets with endophyte (Neotyphodium coenophialum) infected (E+) or noninfected (E-) tall fescue seed. Eighteen crossbred (Angus x Brangus) heifers were assigned to 6 pens and were fed chopped alfalfa hay for 5 d and chopped alfalfa hay plus a concentrate that contained E-tall fescue seed for 9 d during an adjustment period. An 11-d experimental period followed, with animals in 3 pens fed chopped alfalfa hay plus a concentrate with E+ seed and those in the other 3 pens fed chopped hay plus concentrate with E E- seed. Color Doppler ultrasound measurements (caudal artery area, peak systolic velocity, end diastolic velocity, mean velocity, heart rate, stroke volume, and flow rate) and serum prolactin were monitored during the adjustment (baseline measures) and during the experimental period. Three baseline measures were collected on d 3, 5, and 6 during the adjustment period for comparison to post E+ seed exposure. Statistical analyses compared the proportionate differences between baseline and response at 4, 28, 52, 76, 100, 172, and 268 h from initial feeding of E+ seed. Serum prolactin concentrations on both diets were lower (P <0.001) than baseline beginning at 4 h from the start of the experimental period. However, trends in serum prolactin concentrations for heifers on the E- diet suggested ambient temperature was affecting these concentrations. Caudal artery area in E+ heifers had declined (P <0.10) from baseline by 4 h and was consistently lower (P <0.05) for the remainder of the period. Heart rates for E+ heifers were lower than the baseline rate from 4 (P <0.10) to 100 (P <0.001) h, but were similar (P >0.10) to the baseline for 172 and 268 h measures. Blood flow in E+ heifers was consistently lower than the baseline from 4 (P <0.05) to 172 (P <0.001) h, but was similar to the baseline at 268 h when heart rate was similar to the baseline rate. Caudal artery areas for the E- diet were similar to baseline areas except at 100 h when it was greater than baseline. Heart rates and flow rates for E- heifers did not differ (P >0.10) from baseline measures during the experimental period. Results indicated that onset of toxicosis was within 4 h of cattle exposure to E+ tall fescue and is related to vasoconstriction and reduction in heart rate.     

Effects of feeding diets containing endophyte-infected fescue seed on luteinizing hormone secretion in postpartum beef cows and in cyclic heifers and cows.

Two experiments were conducted to investigate the effect of feeding endophyte (Acremonium coenophialum)-infected fescue (Festuca arundinacea Shreb.) seed on LH secretion in postpartum beef cows and in cycling heifers and cows. In Exp. 1, spring-calving primiparous Angus cows (n = 16) were pair-fed for 75 d diets that contained endophyte-free or endophyte-infected (95%) fescue seed that contained 1.3 micrograms/g of ergovaline and 5.2 mg/g of saturated pyrrolizidines. Serial blood samples for basal and GnRH-stimulated serum LH analysis were obtained on d 7, 28, 42, and 56 of the study. The endophyte had no effect on LH secretion (basal, pulse frequency, and amplitude) or milk production. Average daily gain was decreased (P < .05) in cows that consumed infected fescue seed compared with controls (-.20 vs -.01 kg, respectively). Basal serum prolactin concentrations were reduced (P < .01) in treated compared with control cows (8.9 vs 25.4 ng/mL, respectively) on d 70. In Exp. 2, cycling Angus heifers (n = 8; age = 2 yr) and cows (n = 8; age = 4 yr) stratified by age were pair-fed for 40 d diets that contained the noninfected or the highly infected fescue seed. Estrus was synchronized by prostaglandin F2 alpha (d 18 and 28). Serial blood samples for serum LH analysis were obtained on d 28 (luteal phase) and d 30 (follicular phase). The endophyte did not affect LH (P > .28) or prolactin (P > .16) secretion, whereas ADG was decreased (P < .05) in treated compared with control animals (.32 vs .70 kg/d, respectively).     

Effects of endophyte-infected tall fescue on indicators of thermal status and growth in Hereford and Senepol steers

Poor growth often occurs in cattle consuming ergot alkaloids associated with endophyte-infected (EI) tall fescue. Hyperthermia may contribute significantly to poor growth resulting from fescue toxicosis. This study examined indicators of thermal status and growth in Hereford (n = 30; heat-sensitive Bos taurus; H) and Senepol (n = 28; heat-tolerant Bos taurus; S) steers fed EI tall fescue (TF) or orchardgrass (OG) in 2 x 2 factorial experiments. Respiration rates, daytime shade use, tail skin temperatures, and body weights were measured during the summer and fall of 2000 (Exp. 1) and 2001 (Exp. 2). Experimental diets consisted of hay and seed for 12 wk in 2000, hay for 6 wk during the summer of 2001, and hay plus seed for 6 wk during the fall of 2001. In Exp. 1, EI tall fescue increased (P < 0.01) respiration rates, shade use, and skin temperatures in both breeds. Breed x diet affected (P < 0.01) 12-wk ADG in Exp. 1. Growth rate was lower for H-TF (262 g/d) than for S-TF, S-OG, and H-OG (475, 497, and 524 g/d, respectively). In Exp. 2, Senepol had lower (P < 0.01) respiration rates, shade use, and skin temperatures compared with Hereford, but diet did not alter (P > 0.14) these indicator traits in either breed. Breed x diet affected (P < 0.01) summer growth rates. Growth rate was lower for H-TF (88 g/d) than for H-OG, S-TF, and S-OG (508, 555, and 566 g/d, respectively). Adding seed to the diets in Exp. 2 decreased (P < 0.01) ADG for both breeds on TF during the fall. Thermal status indicator traits in Senepol and Hereford steers were similarly altered by TF; however, only Hereford showed consistently poor growth. Senepol showed resilience in their capacity for growth under conditions of fescue toxicosis. Senepol influence may enhance cattle performance in production systems that use EI tall fescue as the base forage.     

Constriction of bovine vasculature caused by endophyte-infected tall fescue seed extract is similar to pure ergovaline

Ergovaline has been extensively used to study vasoactive effects of endophyte- (Neotyphodium coenophialum) infected tall fescue (Lolium arundinaceum). However, initial results indicated that an extract of toxic tall fescue seed (E+EXT) is more potent than ergovaline alone in a right ruminal artery and vein bioassay. The E+EXT induced a greater contractile response than an equal concentration of ergovaline alone in the ruminal artery of heifers (P = 0.018). This led to a hypothesis that other compounds in the seed extract contribute to vasoconstriction. Thus, experiments were conducted to determine if vasoactivity of an E+EXT is different from a mixture of ergot alkaloids (ALK; ergovaline, ergotamine, ergocristine, ergocryptine, ergocornine, ergonovine, and lysergic acid) of similar concentrations and to determine if the vasoactivity of an E+EXT differs from an endophyte-free tall fescue seed extract (E-EXT). Segments of lateral saphenous vein and right ruminal artery and vein were collected from Holstein steers (n = 6) shortly after slaughter. Vessels were cleaned of excess connective tissue and fat and sliced into segments that were suspended in a multimyograph chamber with 5 mL of continually oxygenated Krebs-Henseleit buffer, equilibrated for 90 min, and exposed to a reference compound (120 mM KCl for ruminal vessels and 0.1 mM norepinephrine for saphenous vein). Increasing concentrations of each treatment (E+EXT, E-EXT, ALK, and ergovaline) were added to the respective chamber every 15 min after buffer replacement. Data were normalized as a percentage of maximal contractile response of the reference compound and fit to a sigmoidal concentration response curve. Ergovaline, ALK, and E+EXT induced similar responses in the saphenous vein, ruminal artery, and ruminal vein. The E+EXT displayed a smaller EC(50) (half maximal effective concentration) than ergovaline or ALK in the saphenous vein and ruminal vein (P < 0.008), but not the ruminal artery (P = 0.31). Extrapolated maximum response was greatest in the saphenous vein for ergovaline, least for E+EXT, and intermediate for ALK (P < 0.0001). The E-EXT did not induce a contractile response in any vessel tested (P > 0.1). Data from this study indicate that ergovaline is largely responsible for the locally induced vasoconstriction of bovine vasculature observed with endophyte-infected tall fescue.     

The effect of alkaloids and seed extracts of endophyte-infected tall fescue on prolactin secretion in an in vitro rat pituitary perfusion system.

The objective of this research was to measure the effects of endophyte-infected tall fescue seed extract and various alkaloids associated with the endophyte on in vitro prolactin secretion by rat hemipituitaries. Rat anterior pituitaries (AP) were dissected into halves and placed in temperature-controlled culture chambers (37 degrees C). The tissue was perfused with culture media at a flow rate of 12 mL/h. After perfusion for at least 90 min with control media, AP halves were exposed to their respective treatments for 15 min before they were returned to the control media. The treatments for Exp. 1 were .01 micrograms of alpha-ergocryptine/mL of culture medium, .01 microgram of ergonovine/mL of culture medium, .01 gram-equivalents of endophyte-infected tall fescue seed/mL of culture medium, and .01 gram-equivalents of endophyte free tall fescue seed/mL of culture medium. Treatments for Exp. 2 consisted of 10(-4), 10(-6), and 10(-8) M concentrations of perloline, N-formyl loline, N-acetyl loline, N-methyl loline, and alpha-ergocryptine. alpha-Ergocryptine suppressed (P less than .10) prolactin secretion in both experiments. Ergonovine and perloline both stimulated (P less than .10) prolactin secretion. The loline alkaloids (N-formyl loline, N-acetyl loline, N-methyl loline) had no effect on prolactin secretion. The endophyte-infected seed extract treatment suppressed (P less than .10) prolactin secretion. The endophyte-free seed extract treatment had no effect on prolactin secretion. In Exp. 2, prolactin secretion from AP responded to alpha-ergocryptine treatment in a dose-dependent fashion.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

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)     

Lysocellin effects on growth performance, ruminal fermentation, nutrient digestibility and nitrogen metabolism in steers fed forage diets

Studies were conducted to determine the effects of lysocellin on growth performance and metabolism of steers fed forage-based diets. Treatments in all experiments consisted of 1) control, 2) 100 mg lysocellin/d, 3) 200 mg lysocellin/d and 4) 200 mg monensin/d. In each of two 90-d performance studies, 24 Hereford steers were individually fed greenchop (fungus-free tall fescue and Coastal and Tifton-44 bermudagrass) ad libitum and .91 kg/d of a corn-trace mineral salt supplement. In Exp. 1, tall fescue was fed from d 1 to 45 and bermudagrass from d 46 to 90. Bermudagrass was offered during d 1 to 45 and tall fescue during d 46 to 90 in Exp. 2. Lysocellin improved gain (Exp. 1, P less than .01) and feed conversion (Exp. 1 and 2 combined, P less than .05), decreased total VFA concentrations (P less than .05), increased molar proportions of propionate, isobutyrate and isovalerate (P less than .01), decreased molar proportions of acetate and butyrate (P less than .01) and lowered acetate:propionate (P less than .01). Two metabolism studies involving a total of 16 Hereford steers were conducted. Steers were fed tall fescue greenchop and .91 kg/d supplement for a 34-d adjustment period followed by a 5-d total collection period. Lysocellin increased N digestibility (P less than .01) and N retention (P less than .06) but did not (P greater than .05) affect DM, NDF or ADF digestibility. Data indicate that lysocellin results in major alterations in ruminal fermentation and can increase growth performance and N retention in steers fed forage-based diets.     

The influence of high-nitrogen forages on the voluntary feed intake of sheep

The objective of this research was to examine the effect of high concentrations of nonprotein nitrogen (NPN) on the voluntary food intake of sheep fed high-quality grasses. Wether lambs (n = 6 per treatment) were fed dried switchgrass (Panicum virgatum L.; Exp. 1) or dried tall fescue (Festuca arundinacea Schreb.; Exp. 2). In both experiments, urea was added to the dried forage at 0 (control), 12, or 24 g of N/kg of DM to increase the NPN concentration. Acid detergent fiber concentrations were 305 g/kg of DM in both experiments, although DM digestibility was 663 and 618 g/ kg of DM in Exp. 1 and Exp. 2, respectively. Voluntary feed intake of the control forage was 28.2 and 19.1 g/ kg of BW in Exp. 1 and Exp. 2, respectively, and decreased for the high-urea treatments to 25.2 and 16.2 g/kg of BW in Exp. 1 (P = 0.07) and Exp 2 (P = 0.03), respectively. Total feed N concentrations increased from 29.5 g to 45.7 g of N/kg of DM in Exp. 1 (P < 0.01) and from 28.4 to 55.9 g of N/kg of DM in Exp. 2 (P < 0.01). Nonprotein N concentrations increased from 28.3 to 53.8% of the total N in switchgrass diets (Exp. 1; P < 0.01), and from 26.4 to 64.0% in tall fescue diets (Exp. 2; P < 0.01). Plasma urea concentrations of the lambs increased from 3.1 to 6.6 mM (Exp. 1; P < 0.01) and from 2.9 to 5.8 mM (Exp. 2; P < 0.01) as the amount of urea added to the diets increased. These changes resulted in an increase in plasma osmolality from 298 to 307 mOsm/kg (Exp. 1; P = 0.04), and from 299 to 307 mOsm/kg (Exp. 2; P = 0.06). Increasing feed N and NPN concentrations through the addition of urea caused a significant decrease in the voluntary feed intake of sheep fed tall fescue and switchgrass. These responses showed no significant cause-and-effect relationship between voluntary feed intake, plasma urea concentrations, and plasma osmolality.     

Domperidone can ameliorate deleterious reproductive effects and reduced weight gain associated with fescue toxicosis in heifers

The aim of this study was to evaluate the effect of a dopamine antagonist, domperidone, in nonpregnant, reproductively cycling heifers consuming endophyte-infected (EI) fescue diets. Thirty crossbred heifers (Angus x Holstein or Hereford x Holstein) were assigned to one of three treatment groups (n = 10); endophyte-free (EF) fescue diet, EI fescue diet, or endophyte-infected diet and treated with domperidone (EID). Heifers fed EI diets had decreased weight gains compared with heifers fed EF or EID (P < 0.05) during a 21-d treatment period. Ovarian structures were monitored via transrectal ultrasound to determine follicle size and day of ovulation. Blood plasma samples were collected daily and analyzed for progesterone concentration to determine luteal function. Heifers ingesting EI diets had estrous cycles of shorter duration and lower mid-cycle progesterone concentrations than heifers in the EF or EID treatments (P < 0.05). Ovaries from a subset of heifers in each group (n = 3 per group) were harvested and in vitro secretion of progesterone from luteal tissue extracts was determined. No differences in progesterone concentrations were detected among luteal tissue incubates (P > 0.05). These results suggest that domperidone supplementation of heifers consuming EI fescue may ameliorate certain symptoms of fescue toxicosis.     

Summer fescue toxicity in dairy steers fed tall fescue seed

Seeds of the tall fescue ( Festuca arundinacea Schreb .) cultivars Kentucky 31 and an experimental ryegrass X tall fescue hybrid derivative strain (G1-307), and orchard grass (OG) seed were fed in a carrier diet to calves in controlled environmental rooms (31 to 32 C). Both tall fescue varieties produced symptoms of summer toxicosis in dairy steers. Total feed intake (P less than .01) and water intake (P less than .01) of calves were reduced by the tall fescue seed diets when compared with orchard grass. Steers fed G1-307 and Kentucky 31 tall fescue lost (NS) 17.5 and 7.8 kg of body weight, respectively, while those consuming orchard grass gained (P less than .01) 6.2 kg during the experiment. Rectal temperatures were lower (P less than .05) in the calves fed OG (39.4 C) when compared with those fed G1-307 (40.6 C) and Kentucky 31 (40.8 C) tall fescue seed, respectively. In a second trial Kentucky 31 seed was fed in a carrier diet to Holstein steers at graded levels of 0, 350, 700 and 1,050 g seed/d. Consumption of 700 and 1,050 g seed/d adversely affected performance of steers. Total feed intake was lower and water intake was reduced (P less than .05), with rectal temperatures being elevated (P less than .01) in these two groups when compared with 0- or 350-g treatments. No significant differences were detected in body weight changes in this trial. Respiration rates were not significantly affected in either trial. Results of these trials with the young bovine indicate that a toxic substance(s) is present in tall fescue seed.     

Intake, digestion, and digestive characteristics of Neotyphodium coenophialum-infected and uninfected fescue by heifers offered hay diets supplemented with Aspergillus oryzae fermentation extract or laidlomycin propionate

Tarentaise heifers fitted with a rumen cannula (539 +/- 7.5 and 487 +/- 15.7 kg avg initial BW in Exp. 1 and 2, respectively) were used in two Latin square metabolism experiments having 2 x 2 factorial treatment arrangements to determine the effects of supplementation with Aspergillus oryzae fermentation extract (AO) or laidlomycin propionate (LP) on intake, digestion, and digestive characteristics of Neotyphodium coenophialum-infected (IF) or uninfected (FF) tall fescue (Festuca arundinacea) hay diets consumed ad libitum. Heifers were housed in individual stanchions in a metabolism facility with ambient temperatures controlled to range between 26.7 and 32.2 degrees C daily. Total feces and urine were collected for 5 d following a 21-d dietary adaptation period. In situ DM and NDF disappearance and ruminal fermentation characteristics were also determined. In Exp. 1, DMI was 24% greater (P < 0.01) by heifers offered FF than by those offered IF (6.7 vs 5.4 kg/d). Heifers fed 2 g/d AO tended (P = 0.09) to consume 4% more DM than those fed a diet without AO. Degradable DM and NDF fractions of IF were greater (P < 0.01) than those of FF, but AO supplementation did not affect situ disappearance (P > or = 0.42). In Exp. 2, DMI was 18.9% greater (P < 0.01) by heifers offered FF than by those offered IF (6.6 vs 5.5 kg/d). Heifers fed LP (50 mg/d) consumed 10.6% less (P < 0.05) DM than those not fed LP (5.7 vs 6/5 kg/d). Digestibility of NDF tended to be greater (P = 0.08) and digestibility of ADF was greater (P < 0.05) from FF than from IF. Conversely, apparent N absorption (%) was greater (P < 0.05) from IF than from FF. Heifers fed LP had lower (P < 0.05) ADF digestibility than those not fed LP. In situ degradable DM and NDF fractions were greater (P < 0.01) from IF than from FF. Diets supplemented with LP had higher (P < 0.01) indigestible DM and NDF fractions than those without LP. Propionic acid and total VFA concentrations were greater (P < 0.05) from heifers offered FF than from those offered IF and from heifers fed LP than from those not fed LP. Therefore, it appears the major effect of N. coenophialum was a reduction in forage intake and total-tract fiber digestibility in certain situations. Response to the feed additives was similar whether heifers were offered IF or FF and no evidence was apparent that either additive would improve performance substantially by animals consuming low-quality fescue hay diets.     

Effects of feeding Kentucky 31 tall fescue seed infected with acremonium coenophialum to laboratory rats

An endophytic fungus found in Kentucky 31 (KY-31) tall fescue has been associated with the "summer syndrome" (fescue toxicity) in grazing cattle. Four experiments were conducted to investigate the use of weanling rats as an animal model to study the fescue toxicity syndrome. When graded levels of fungus-infected (INF) or fungus-free (FF) KY-31 seed were fed, feed intake and growth rates were inversely related to the amount of INF seed in the diet. When diets containing 50% seed were fed, rats eating INF seed had reduced (P less than .05) daily water consumption (9 vs 20 ml) and lowered (P less than .05) body temperatures (36.8 vs 37.7 C) when compared with the FF treatments. Autoclaving the seed increased feed intake and growth rate of rats receiving both INF and FF seed diets, but daily gains continued to be less (P less than .05) in the rats fed autoclaved INF diets when compared with rats fed autoclaved FF diets (2.3 vs 6.8 g). Rats fed diets containing either 40% shredded wheat on which the fescue endophyte had been grown or 40% shredded wheat that was not innoculated did not differ in performance. Crude fiber, nitrogen-free extract, gross energy and dry matter digestibilities were enhanced (P less than .05) by the presence of INF seed in the diets when compared with the FF seed treatments. Crude protein and ether extract digestibilities and apparent biological value of fescue protein were not affected by presence of the fungus. The effect of INF seed on organ weights was inconsistent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of level of endophyte infection, nitrogen fertilization rate, grazing period, and paddock exchange on some chemical properties of four bovine tissues.

Three grazing experiments were conducted to determine the effect of level of endophyte infection, rate of N fertilization of tall fescue grass, grazing period, and paddock exchange on selected chemical properties of four bovine carcass tissues. Samples of semitendinosus and longissimus muscle and of subcutaneous and perinephric adipose tissue were excised from the left side of each carcass. In Exp. 1, percentage of stearic acid was higher (P less than .05) and percentages of palmitoleic and oleic acid were lower (P less than .05) in all tissues from steers grazed on LELN Au-Triumph fescue than in tissues from steers grazed on LELN KY-31 fescue. Grazing periods of 175 or 245 d or paddock exchange (Exp. 2) had no significant effect on proximate composition of semitendinosus and longissimus muscles; however, moisture content was higher (P less than .05) in the semitendinosus muscle from steers grazed on 100% (100E) endophyte-infected KY-31 fescue. Forage treatment, grazing period, and paddock exchange (Exp. 2 and 3) had no significant effect on percentage of saturated fatty acids in the subcutaneous, semitendinosus, and longissimus tissue samples. In Exp. 2 and 3, percentages of saturated fatty acids were higher (P less than .05) in subcutaneous and perinephric adipose tissue samples from steers grazed on 100E than in samples from steers grazed on zero endophyte (OE) fescue.(ABSTRACT TRUNCATED AT 250 WORDS)     

不同品种草坪型羊茅种子生产性能研究

经过3年的试验,对引自美国和加拿大的9种草坪型羊茅在引黄灌区的物候期、生长特性以及种子生产性能进行了较为系统的研究。结果表明,所有参试品种在银川地区均可良好结实,但结实性能差异极大,Lowgrow,Arid高羊茅和Ruby及Boreal紫羊茅的种子产量最高。通过试验认为,在宁夏引黄灌区建立草坪型羊茅种子生产基地是完全可行。     

Effect of ergot alkaloids on contractility of bovine right ruminal artery and vein

Ergot alkaloids produced by the endophyte (Neotyphodium coenophialum) associated with tall fescue (Lolium arundinaceum) are implicated in the clinical signs of fescue toxicosis. These compounds were hypothesized to correspondingly affect foregut vasculature. The objective of this study was to determine vasoconstrictive potentials of ergovaline, ergotamine, ergocryptine, ergocristine, ergonovine, ergocornine, and lysergic acid on right ruminal artery and vein. Segments of right ruminal artery and vein were collected from the ventral coronary groove of predominantly Angus heifers (n = 10) shortly after slaughter and placed in a modified Krebs-Henseleit buffer on ice. Vessels were cleaned of excess connective tissue and fat, sliced into 2- to 3-mm segments, and suspended in a multi-myograph chamber with 5 mL of continuously oxygenated Krebs-Henseleit buffer (95%O(2)/5% CO(2); pH 7.4; 37°C). Arteries and veins were equilibrated to 1.0 and 0.5 g, respectively, for 90 min followed by the reference addition of 120 mM KCl. Increasing concentrations of each alkaloid were added to the respective chamber every 15 min after buffer replacement. Data were normalized as a percentage of the contractile response induced by KCl. Alkaloid (P < 0.0001), concentration (P < 0.0001), and vessel type (artery or vein; P = 0.004) affected contractility. No arterial response was observed until 10(-6) M for ergovaline and ergotamine; 10(-5) M for ergocryptine, ergocornine, and ergonovine; and 10(-4) M for ergocristine. Lysergic acid did not induce a contractile response in the ruminal artery. No venous contractile response was observed until concentrations of 10(-6) M for ergovaline, 10(-5) M for ergotamine, and 10(-4) M for ergocryptine and ergocristine were achieved. Lysergic acid, ergonovine, and ergocornine did not induce a contractile response in the ruminal vein. A greater arterial maximal response was observed for ergovaline (P < 0.0001), whereas the arterial and venous responses were not different for ergotamine (P = 0.16), ergocryptine (P = 0.218), and ergocristine (P = 0.425). These results indicate that ergot alkaloids associated with toxic endophyte-infected tall fescue are vasoactive and can potentially alter arterial blood supply and venous drainage from the bovine foregut.     

不同收获期高羊茅种子活力测定方法的比较研究

通过七种生理生化方法测定１９９５和１９９６年不同成熟时期收获的Ｆａｗｎ和Ｓａｆａｒｉ高羊茅种子活力。试验结果表明,加速老化和ＡＴＰ地是测定高羊茅种子活力的较好方法,电导率、发芽指数和活力指数测定应以完全成熟的种子为宜,而温室出苗率和千粒重的测定效果不佳。     

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.     

Effects of supplemental Bermuda grass hay or corn on intake, digestion and performance of cattle consuming endophyte-infected fescue

Effects of supplemental Bermuda grass hay (BG) or ground corn on intake, digestion and performance of cattle consuming endophyte-infected fescue (I) were studied. In Exp. 1, a Latin square study, five growing Holstein steers (158.1 kg) consumed I ad libitum and were offered 0, .3, .6, .9 or 1.2% body weight (BW) of BG daily. Total dry matter (DM) intake rose linearly (P less than .05) with increasing BG, although intake was numerically similar with .6, .9 and 1.2% BW of BG. Digestibility was constant with diet (P greater than .10). Six growing Holstein steers used in Exp. 2, a Latin square with a 2 x 3 factorial arrangement of treatments, ingested I or noninfected (NI) fescue hay ad libitum with 0, .5 or 1.0% BW of ground corn. Total DM intake increased linearly as the level of corn rose (P less than .05). Total intake with I increased more with the first than with the second addition of corn, and the opposite occurred with NI (interaction between fescue infection and the quadratic effect of corn level, P less than .10). Organic matter digested (g/d) was greater for NI than for I and rose linearly with increasing corn ingestion (P less than .05). Ninety-six crossbred beef heifers and steers (184.2 kg avg initial live weight) were used in a 77-d fall grazing experiment (Exp. 3) with a 2 x 3 factorial treatment arrangement. Cattle grazed I or NI paddocks and were given no supplement or .34% BW of BG or .65% BW of ground corn on a daily basis (DM).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.