Effects of diet on rumen proliferation and fecal shedding of Escherichia coil O157:H7 in calves.

Calves inoculated with Escherichia coli O157:H7 and fed either a high-roughage or high-concentrate diet were evaluated for rumen proliferation and fecal shedding of E. coli O157:H7. Calves fed the high-roughage diet had lower mean rumen volatile fatty acid concentrations and higher rumen pH values than did calves fed the high-concentrate diet. Despite these differences in rumen conditions, the calves fed the high-roughage diet did not have greater rumen populations of E. coli O157: H7 and did not exhibit increased or longer fecal shedding compared with the calves fed the high-concentrate diet. Two calves shedding the highest mean concentrations of E. coli O157:H7 were both fed the high-concentrate diet. There was a significant (P < 0.05) positive correlation between fecal shedding and rumen volatile fatty acid concentration in calves fed a high-concentrate diet. The effects of diet on E. coli O157:H7 proliferation and acid resistance were investigated using an in vitro rumen fermentation system. Rumen fluid collected from steers fed a high-roughage diet, but not from steers fed a high-concentrate diet, supported the proliferation of E. coli O157:H7. Rumen fluid from steers fed a high-concentrate diet rapidly induced acid resistance in E. coli O157:H7. The impact of diet on fecal shedding of E. coli O157:H7 is still unclear and may depend on dietary effects on fermentation in the colon and on diet-induced changes in the resident microflora. However, rapid development of acid tolerance by E. coli O157:H7 in the rumens of calves fed high-concentrate diets, allowing larger populations to survive passage through the acidic abomasum to proliferate in the colon, may be one factor that influences fecal shedding in cattle on feed.

Fecal shedding and rumen growth of Escherichia coli O157:H7 in fasted calves.

Nine weaned calves aged from 8 to 12 weeks were fitted with rumen cannulas and were inoculated by cannula with 10(10) CFU of a five-strain mixture of nalidixic acid-resistant Escherichia coli O157:H7. Six calves were fasted for 48 h on days 15 and 16 and days 22 and 23 after inoculation. Samples of rumen contents and feces were obtained daily to enumerate E. coli O157:H7 populations and to determine rumen volatile fatty acid (VFA) concentrations and rumen pH. Fasting resulted in a marked decrease in rumen VFA concentrations from a mean of 135 mmol/liter before the fast to a mean of 35 mmol/liter during the second day of the fast. However, there was no correlation between daily VFA concentration and daily rumen or fecal numbers of E. coli O157:H7 in any of the calves. Fasting generally had no significant effect on the rumen or fecal numbers of E. coli O157:H7. The exception was a single fasted calf that experienced a 3-log(10) CFU/g increase in fecal shedding during and after the first fast. Despite the consistent changes in VFA concentrations in fasted calves, the fluctuations in rumen numbers of E. coli O157:H7 in the rumen of fasted calves were minimal. At the end of the experiment, E. coli O157:H7 was detected in either the rumen or omasum in two of three control calves at necropsy and in either the rumen or reticulum in five of six fasted calves. E. coli O157:H7 was detected in the colon in two of three control calves and in six of six fasted calves at necropsy. These results suggest that in cattle already shedding E. coli O157:H7, feed withdrawal and the associated changes in rumen pH and VFA concentrations have little effect on fecal shedding and rumen proliferation of E. coli O157:H7.

Screening nitrate in forages with a test strip: collaborative study.

A collaborative study was conducted for screening nitrate in forages with a commercially available test strip. The method involves extracting a finely ground sample with deionized water. The test strip is dipped in the sample extract. The color of the reaction zone on the test strip changes from white to pink or purple depending on the nitrate concentration in sample extract. The nitrate present in the extract is determined by comparing the color of the test strip to the color scale on the test strip container. Six blind quintuplicates of forage samples were analyzed by 20 collaborators. Nitrate concentrations in forage samples tested ranged from < 1000 ppm nitrate to > 10,000 ppm nitrate on dry matter basis. Each collaborator was asked to assign each sample to one of the 4 following nitrate concentration ranges: (1) < 1000 ppm, (2) 1000 to 5000 ppm, (3) > 5000 ppm to 10,000 ppm, and (4) > 10,000 ppm. Nineteen of 20 collaborators reported results. Results from 2 laboratories were rejected as outliers by inspection and chi 2 test. Sensitivity rates (p+) ranged from 0.965 to 0.998, with standard errors of 0.006 to 0.16. Specificity rates (p-) ranged from 0.991 to 0.997 for the 4 ranges, with standard errors of 0.003 to 0.006. False-positive rates (pf+) ranged from 0.006 to 0.046, with standard errors of 0.006 to 0.025. False-negative rates (pf-) ranged from 0.003 to 0.007, with standard errors of 0.003 to 0.006. Screening nitrate in forages with a test strip has been adopted first action by AOAC INTERNATIONAL.

Aflatoxin contamination of corn used as bait for deer in the southeastern United States.

Samples of shelled corn used for wildlife feed were taken from bait piles and storage bins in North Carolina and South Carolina (USA) from 29 September through 28 November 1993, and were analyzed for aflatoxin. Twenty (51%) of 39 samples were positive, with aflatoxin levels ranging from a trace to 750 parts per billion. Based on the high prevalence of aflatoxin-contaminated corn, exposure of wild-life to aflatoxin undoubtedly occurs, although the effects of such exposure are largely unknown.

Effects of various known and potential cyanide antagonists and a glutathione depletor on acute toxicity of cyanide in mice.

To compare the protective potencies of a large number of known and potential cyanide antagonists in one stock of mice, groups (N = 10) of male CF-1 Swiss-Webster mice were given a single maximal or near-maximal intraperitoneal injection of each substance. Ethyl maleate, a glutathione (GSH) depletor and potential enhancer of cyanide toxicity, was given to other groups. Thirty min later, the mice were given subcutaneous injections of graded doses of KCN. In untreated control mice, the 24-hr median lethal dose (LD50) of KCN was 11 mg/kg of body weight (potency ratio, PR = 1.0). In comparison, protective effects of traditional antagonists thiosulfate and nitrite produced PR values of 1.48 and 2.95, respectively. Tetrathionate, sulfate, dithionite, methionine, hydroxocobalamin, ascorbate, pyridoxal phosphate, alpha-ketoglutarate, alpha-ketobutyrate, GSH, GSH disulfide (GSSG) and selenite were similar in efficacy to thiosulfate (P less than 0.05; PR values 1.35-1.59). Cysteine, diethyldithiocarbamate (DEDC), and cobaltous chloride were more effective than thiosulfate (PR values 1.68, 1.69, and 1.85, respectively). Phentolamine and dicobalt EDTA were ineffective, whereas papaverine enhanced toxicity (PR 0.72). Agents with significant PR values (greater than or equal to 1.14) but which were less effective than thiosulfate included sulfite, dimercaptosuccinic acid, pyruvate, citrate, alpha-ketovalerate, naloxone, and corn oil. Ethyl maleate in corn oil markedly enhanced KCN lethality (PR 0.57 compared to corn oil alone), and caused prolonged illness in several mice. Vitamin E in corn oil had no effect. Dual mixtures of thiosulfate with other selected substances were also tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Zinc-induced hemolytic anemia caused by ingestion of pennies by a pup.

A 4-month-old Pomeranian pup was examined because of anorexia, salivation, and persistent vomiting. Initial laboratory testing revealed marked hemolytic anemia with spherocytosis. Survey abdominal radiography revealed 4 metal objects which, when removed by gastrotomy, were identified as pennies. Of 4 pennies, 3 were minted since 1983 and were heavily pitted over the surface and rim. Partially digested pennies were composed of a copper-plated high zinc concentration alloy. Further laboratory testing indicated a marked increase in serum zinc concentration in the pup (28.8 mg/L), confirming metal toxicosis. Serum zinc concentrations decreased during recovery.

Induced aflatoxicosis in rabbits: blood coagulation defects.

The effect of acute and subchronic experimental aflatoxicosis on blood clotting activity and platelets was evaluated. Male New Zealand White rabbits (weighing 2.4-3.2 kg each) were used. In Experiment 1, 19 rabbits were given orally 0.05 mg of aflatoxin B1 (AFB1)/kg of body weight daily from Day 0 through Day 23. Blood samples were collected before dosing and on Days 2, 5, 9, 12, 16, 19, and 23 of the experimental period. In Experiment 2, 40 rabbits were given a single dose of 0.4 mg of AFB1/kg of body weight. Blood samples were collected before dosing and at 12, 24, 36, and 48 hr after dosing. When compared to baseline and control animal values, one-stage prothrombin times and activated partial thromboplastin times of aflatoxin-dosed rabbits were lengthened, and there was a statistically significant decrease in fibrinogen, Factor IX, VIII, and V activities. Platelet counts were significantly increased in subacutely exposed rabbits, and platelet size was decreased in single high-dose treated groups. Factor deficiencies were attributed to a combination of decreased factor synthesis from hepatic insufficiency and consumptive coagulopathy or primary fibrinolysis.

Pseudohyperchloremia associated with bromide intoxication in a goat herd.

Pseudohyperchloremia and a negative anion gap were detected in goats with bromide intoxication. Bromide interferes with ion-specific electrodes, resulting in a falsely increased serum chloride concentrations. Bromide intoxication should be considered in animals with progressive neurologic signs, a high serum chloride value, and a low or negative anion gap.

Caprine aflatoxicosis: experimental disease and clinical pathologic changes.

Groups of 8 male crossbreed domestic goats were given 3 dosage levels of aflatoxin B1 [(AFB1) mg/kg of body weight/day] orally: 0.1 for 34 days; 0.2 for 18 days; or 0.4 for 10 days. Clinical condition, feed consumption, and selected blood values were determined. Clinical signs of toxicosis included decreased feed consumption, slight-to-moderate loss of body weight, mucopurulent nasal discharge, dyspnea, coughing, lethargy, icterus, diarrhea (4 goats), and subnormal body temperature 24 to 48 hours before death. Clinicopathologic changes included increases in total RBC count, PCV, hemoglobin concentration, serum bilirubin concentration, and serum activities of aspartate aminotransferase, isocitric dehydrogenase, and ornithine carbamyl transferase. Goats given the 2 smaller dosage levels of AFB1 had slight increases of serum total protein (TP) concentration compared with control goats, but goats given the larger dosage levels of AFB1 initially had a slight decrease in TP. Aflatoxin had little effect on total WBC count. Serum alanine aminotransferase (ALT) activities in goats given the 2 larger dosage levels of AFB1 were similar to those of control goats, but goats given the smallest dosage level of AFB1 had increased serum ALT activities. Aflatoxin did not produce consistent dose-related changes in serum alkaline phosphatase activities. Seemingly, goats are susceptible to aflatoxin. Onset of clinical signs was dose-related. Onset and magnitude of increases in PCV, hemoglobin concentration, serum bilirubin concentration, and activities of serum aspartate aminotransferase, ornithine carbamyl transferase, and isocitric dehydrogenase were dose-related. Changes in TP and activities of serum ALT and alkaline phosphatase were neither dose-related nor were they potentially useful indicators of toxicosis.

Caprine aflatoxicosis: serum electrophoresis and pathologic changes.

Pathologic changes and serum electrophoretic patterns were determined in 30 male goats given aflatoxin B1 (AFB1) orally at 4 dosage levels (mg/kg of body weight/day): 0.1 for 34 days; 0.2 for 18 days; 0.4 for 10 days; or 0.0 for 29 days. Goats given AFB1 had increased mean concentrations of gamma-globulins and most had decreased mean concentrations of beta-globulins, although these changes in serum proteins were not significant (P greater than 0.05). At necropsy, ascites, pale livers, petechial hemorrhages, nasal discharge, and icterus were present. Microscopic changes included bile ductule proliferation, hepatocytic karyomegaly, hepatocellular degeneration, pneumonia, rhinitis, and proximal renal tubular nephrosis. Goats given the 2 smaller dosage levels of AFB1 lived longer and had more severe lesions. Goats may be a good model for the study of ruminant aflatoxicosis.

Effect of enzyme inducers and inhibitors and glutathione precursor and depleter on induced acute aflatoxicosis in rabbits.

Male New Zealand White rabbits were treated with microsomal enzyme inducers, inhibitors of hemoprotein synthesis or action, and glutathione precursor and depletor before they were orally given the median lethal dose (LD50) of aflatoxin B1 (AFB1; 0.4 mg/kg) at the start of a 7-day experimental period. The drugs administered, mean duration of illness (hours), and survival percentage were as follows: controls (saline solution)-85, 50%; phenobarbital (PB)-100, 100%; phenylbutazone-115, 67%; benzoflavone-39, 17%; stanozolol-67, 67%; cobaltous chloride (CoCl2)-46, 67%; piperonyl butoxide (PBO)-88, 100% cysteine (CYS)-68, 100%; ethyl maleate-71, 83%. Signs of toxicosis included decreased feed and water consumption, weight loss, dehydration, lethargy, and emaciation; some rabbits died or were euthanatized. Clinico-pathologic changes included increased serum aspartate aminotransferase (AST) activity by 24 hours and bilirubin concentration by 48 to 72 hours after AFB1 was given. Grossly, livers were pale or tan and friable, with prominent lobular architecture. Kidneys of affected rabbits were pale to dark red. Microscopically, livers were normal or had lesions as great as extensive necrosis, hemorrhage, mineralization, and bile duct proliferation. Treatment of rabbits with PB, CoCl2, PBO, and CYS protected against AFB1 hepatic pathology, and PB, PBO, and CYS also had protective effect against lethality. Ethyl maleate provided some protection against lethality and increased serum AST activity and bilirubin concentration. Toxicosis was enhanced by benzoflavone; phenylbutazone and stanozolol had litte influence.

Effect of some enzyme inducers, fluids, and methionine-thiosulfate on induced acute aflatoxicosis in goats.

Groups of four 6- to 12-month-old male goats were injected intraruminally with a lethal dose (3 mg/kg of body weight) of aflatoxin B1 (AFB1). Drugs were administered parenterally before (pretreatment) or beginning 8 hours after goats were doses with AFB1. These drugs were phenobarbital (PB), phenylbutazone (PBZ), piperonyl butoxide (PRO), benzoflavones, water, and 5% glucose solution (D5W). Most groups given the drugs after AFB1 was administered also were given intraperitoneal injections of methionine-sodium thiosulfate (MET-TS) solution. Clinical signs of toxicosis, serum aspartate aminotransferase activities, serum bilirubin concentrations, duration of illness, mortality, and gross and microscopic pathologic findings taken together indicated that toxicosis was increased with MET-TS + PB therapy, PBZ pretreatment, PBZ therapy, benzoflavone pretreatment, benzoflavone therapy, MET-TS + benzoflavone therapy, and MET-tS + water therapy. Toxicosis was not altered appreciably by MET-TS + PBO therapy. Beneficial effects (less severe toxicosis) were produced by PB pretreatment; these effects were prolonged maintenance of strength, vigor, and appetite and (in 1 goat that recovered) absence of pathologic changes or serum bilirubin increase. Therapy with MET-TS + D5W (but not MET-TS alone) also lengthened maintenance of strength, vigor, and appetite, but did not prevent pathologic changes. The beneficial effect of MET-TS therapy reported in a previous study (AFB2 dosage of 4 mg/kg) was not observed with the 3 mg/kg lethal dose. In conclusion, therapy for acute aflatoxicosis with inducers of hepatic microsomal enzymes is ineffective (PBO) or contraindicated (PB, PBZ, benzoflavones). Therapy with D5W may be a useful adjunct to other therapeutic drugs, but multiple intraperitoneal injections of D5W may decrease survival time because of stress.

Effects of various treatments on induced chronic aflatoxicosis in rabbits.

Male New Zealand White rabbits were orally given 0.05 mg of aflatoxin B1 (AFB1)/kg of body weight daily for 10 days and were treated with glutathione-precursors and depletor, antibacterial agents, or sodium thiosulfate. The drug administered, the mortality, and the mean survival time were as follows: corn-oil controls (0), euthanatized at 25 days; AFB1-controls (2), 21 days; AFB1 and saline controls (2), 22 days; cysteine and AFB1 (5), 13 days; methionine and AFB1 (5), 12 days; sodium thiosulfate and AFB1 (2), 21 days; sulfadimethoxine and AFB1 (1), 24 days; oxytetracycline and AFB1 (0), euthanatized at 25 days; and ethyl maleate and AFB1 (3), 21 days. Clinical signs of toxicosis included decreased feed consumption during AFB1 administration, loss of body weight or failure to gain, and death. Clinicopathologic changes included increases in serum bilirubin concentration and alanine aminotransferase and aspartate aminotransferase activities. Prothrombin and activated partial thromboplastin times were lengthened. Plasma fibrinogen concentration was decreased. Changes in PCV, hemoglobin concentration, and serum alkaline phosphatase were unremarkable. Oxytetracycline had protective effects against chronic aflatoxicosis in rabbits. Cysteine and methionine enhanced chronic aflatoxicosis.

Toxicologic study of carboxyatractyloside (active principle in cocklebur--Xanthium strumarium) in rats treated with enzyme inducers and inhibitors and glutathione precursor and depletor.

Male rats (10 rats/group) were treated with phenobarbital (PB), phenylbutazone (PBZ), stanozolol (3 inducers of cytochrome P450-dependent enzymes), piperonyl butoxide (PBO; a P450 inhibitor), cobaltous chloride (CoCl2; an inhibitor of hemoprotein synthesis), 5,6-benzoflavone (BNF; an inducer of cytochrome P448 dependent enzymes), cysteine [CYS; a glutathione (GSH) precursor], or ethyl maleate (EM; a GSH depletor). The rats were then given a calculated LD50 dosage (13.5 mg/kg of body weight) of carboxyatractyloside (CAT) intraperitoneally. Clinical signs of toxicosis, duration of illness, lethality, gross lesions, and hepatic and renal histopathologic lesions were recorded. Seemingly, (i) CAT toxicosis has independent lethal and cytotoxic components (PBZ decreased lethality and cytotoxicity; CoCl2 decreased cytotoxicity but not lethality; BNF decreased duration of illness, and perhaps lethality, but not cytotoxicity); (ii) CAT cytotoxicity could be partly due to an active metabolite formed by de novo-synthesized, P450-/P448-independent hemoprotein (PBZ and CoCl2 had anticytotoxic effects, but PB, stanozolol, PBO, and BNF did not); (iii) CAT detoxification may occur partly through a hemoprotein-independent, PBZ-inducible enzyme, and partly through a P448-dependent (BNF-inducible) enzyme; and (iv) CAT detoxification apparently is not P450 or GSH-dependent because PB, stanozolol, and CYS had no beneficial effects, and PBO, CoCl2, and EM did not enhance toxicosis. Metabolism of CAT may have a role in its cytotoxic and lethal effects.

Abnormal concentrations of B vitamins and amino acids in plasma and B vitamins in bile of rabbits with aflatoxicosis.

The dosages of aflatoxin B1 (AFB1) required to produce significant changes in concentrations of B vitamins in plasma and bile and of amino acids in plasma of rabbits were determined. Folate increased by 98% in plasma, whereas concentration of thiamine, vitamin B6, and biotin decreased by more than 50%. In bile, choline and biotin increased 14- and 18-fold, respectively, whereas folate and niacin decreased by more than 50%. All amino acids in plasma increased between 76 and 155%. The dosages of AFB1 required to induce these changes were usually between 12.5 and 37.5 microgram/kg of body weight per day. Except for changes in biliary concentrations of pantothenic acid, folic acid, and biotin, lower threshold dosages of aflatoxin were required to produce weight loss and anorexia (5.0 and 8.5 microgram of AFB1/kg per day, respectively) than for changes in vitamins and amino acids (approximately 25 to 50 microgram of AFB1/kg per day). The data indicated that AFB1 interfered with the metabolism of B vitamins and amino acids in rabbits.

Determination of aflatoxins in compound feedstuffs containing citrus pulp.

A method is described for determining aflatoxins B1, B2, G1, and G2 in compound feedstuffs containing citrus pulp. A finely ground sample is extracted with methylene chloride in a blender and cleaned with lead acetate. An aliquot of the cleaned extract is partitioned into methylene chloride and evaporated to dryness. The residue is dissolved in 0.5 mL chloroform. A 10 muL sample is applied to a thin layer chromatographic (TLC) plate and developed in 2 dimensions. Aflatoxins B1, B2, G1, and G2 are resolved and quantitated visually. The average recoveries were 96, 104, 98, and 102%, respectively. As little as 5 micrograms aflatoxin B1 or G1/kg, and 1.5 micrograms aflatoxin B2 or G1/kg can be determined by this procedure.