Ergot alkaloids cause fescue toxicosis when livestock graze endophyte-infected (E+) tall fescue. Little is known about the bioavailability of the ergot alkaloid classes (lysergic acid, lysergic acid amides, or ergopeptine alkaloids) in livestock, and this hampers development of pharmacological strategies to ameliorate the toxicosis. One method used to determine bioavailability of ergot alkaloids is to examine urinary and biliary excretion patterns. Thus, our objectives were to compare ergot alkaloid excretion via urinary or biliary systems and to determine the rate of appearance or clearance of these alkaloids in cattle that were grazing E+ or endophyte-free (E-) tall fescue. In autumn 1996, bile and urine samples were collected from eight steers (203 kg), each grazing E+ and E- tall fescue, and total alkaloid excretion was quantified using competitive ELISA. Approximately 96% of the ergot alkaloids were excreted in urine. The same steers were used to examine the rate of appearance in, or clearance from, urine when switched from E+ to E-, or from E- to E+, pastures in comparison with steers that were continuously grazing E+ or E- tall fescue at 0, 2, 5, and 7 d. Steers were returned to their original pastures after 7 d, and urine was collected at 2, 5, and 7 d. Urinary alkaloid concentrations in steers switched from E- to E+ pastures were similar (P = .55) to those in steers that continuously grazed E+ tall fescue after 2 d. Steers switched from E+ to E- pastures had urinary alkaloid concentrations similar (P = .91) to those in steers that continuously grazed E- pastures after 2 d. In 1997, two trials were conducted in which steers (191 kg) were switched or remained on E+ or E- pastures, and urine was collected at 0, 12, 24, 48, and 96 h to estimate rate of alkaloid appearance or clearance. Steers switched from E- to E+ 1) had about 33% as much urinary alkaloids as steers grazing E+ pasture after 12 h, 2) were not different after 24 h (P = .76), 3) had twice those of the E+ steers at 48 h (P < .05), and 4) were not different after 96 h. Steers switched from E+ to E- tall fescue had approximately 33% less (P < .05) urinary alkaloids than those grazing E+ at 12 h, 67% less (P < .05) at 24 and 48 h, and were not different (P = .86) from steers continuously grazing E- pastures after 96 h. Urinary alkaloid excretion patterns were similar to ergot alkaloid solubility patterns from in vitro digestion of E+ tall fescue. We suggest that alkaloids, liberated from the forage by ruminal microorganisms, were rapidly absorbed as lysergic acid amides and biotransformed ergopeptine alkaloids.

Circumstantial evidence suggests ergovaline is the putative toxin causing fescue toxicosis. However, several investigators suggest lysergic acid may be involved as well. Therefore, the purpose of this study was to (i) determine the metabolic fate of ergot alkaloids in ruminants, (ii) investigate gastric transport, and (iii) validate these findings in vivo. Ruminal metabolism of the alkaloids was determined by inoculating endophyte‐infected and endophyte‐free tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] with viable and nonviable ruminal fluid using in vitro techniques. Total ergot alkaloid concentration increased with time due to microbial metabolism. The alkaloids were extracted, and ruminal and omasal transport investigated in vitro. Only lysergic acid crossed gastric barriers. To validate the findings, fistulated steers were allowed to graze endophyte‐infected or endophyte‐free tall fescue paddocks in a crossover study, and ruminal fluid and urine were analyzed for ergot alkaloids over time. Ergovaline was not found in ruminal fluid or urine. Urine was immunopurified from a steer grazing endophyte‐infected tall fescue and analyzed by high‐performance liquid chromatography. A peak with a signal consistent with lysergic acid was found. These results imply that lysergic acid may be involved in the fescue toxicosis syndrome.

Spectral analysis was used to relate dietary quality and herbage species to the behavior of grazing steers. Four .3-ha paddocks were established with either 'AU-Triumph' tall fescue (F; Festuca arundinacea Schreb.), 'Apollo' alfalfa (A; Medicago sativa L.), 1/3 fescue and 2/3 alfalfa (2/3A), or 2/3 fescue and 1/3 alfalfa (1/3A). Each paddock was stocked with 10 to 16 steers and defoliated in 5 d. Three steers on each paddock carried vibracorders to monitor grazing time. Daily forage samples were taken in 10-cm layers and weighed. Esophageal extrusa were collected from fistulated steers to measure diet quality. Daily grazing time did not differ (P = .37) among treatments; however, steers grazing mixtures grazed numerically longer (1.4 h/d) than steers on monocultures. Spectral analysis revealed that steers grazing A and 2/3A had many daily meals of short duration, but steers grazing 1/3A and F consumed three meals daily at 8-h intervals. Throughout the 4.67-d grazing period, quality of the diet linearly declined in crude protein and herbage digestibility, linearly increased in neutral detergent fiber and cellulose, and exhibited quadratic changes in lignin and ash. For most quality values, the tall fescue monoculture differed from the others (P < .05). Steers selected diets with similar quality for the A, 2/3A, and 1/3A treatments. This study illustrates how differences in forage diets alter grazing behavior of steers.

Grazing and fertilization effects on long‐term persistence of novel‐endophyte‐infected tall fescue (TF) have not been well documented. A field study was conducted for 6 years to assess; (i) persistence of TF under grazing conditions; and (ii) production and performance of yearling heifers on wild‐endophyte‐infected, novel‐endophyte‐infected, and endophyte‐free TF associations fertilized with either inorganic N‐P‐K or broiler litter. Average daily gain (ADG) (1.5 ± 0.2 lb/day; mean ± standard deviation among 6 years) and cattle body weight (BW) gain on a yearly basis (487 ± 147 lb/acre) were as good with broiler litter as with inorganic fertilization (P > 0.1), although seasonal shifts occurred. ADG on TF pastures with novel endophyte (1.7 lb/day) was as good as, and in one year was even better than (P < 0.1), with endophyte‐free association (1.6 lb/day), both of which were superior to ADG on wild‐endophyte‐infected tall fescue (1.2 lb/day). Persistence of TF with novel endophyte (73% basal area) was intermediate between wild endophyte (76%) and endophyte free (67%). With excellent ADG and stand persistence, novel‐endophyte‐infected TF should be recommended for establishment of new, sustainable, cool‐season pastures in the Piedmont region and these pastures can be effectively fertilized with broiler litter.

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