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Biomedical subjects

L W George

Publications and source records attributed to L W George.

At least 37 records · Page 2Linked to original sources
PubMed1988

Light and electron microscopic changes in corneas of healthy and immunomodulated calves infected with Moraxella bovis.

Thirty-nine Holstein calves (50 to 100 kg and 2 to 3 months old) were randomly assigned to 4 groups. Calves in group I (n = 12) were inoculated with Moraxella bovis and were euthanatized 24 hours (6 calves) or 8 days after inoculation (6 calves). Group-II calves (n = 12) were treated with hydroxyurea for 6 days, and then 6 of these calves were inoculated with M bovis. The daily hydroxyurea treatments continued for 14 days, and then all calves in group II were euthanatized. Group-III calves (n = 9) were administered dexamethasone parenterally, beginning 24 hours before inoculation with M bovis, and then daily thereafter, until they were euthanatized at either 24 hours (n = 5) or 8 days (n = 4). Group-IV calves (n = 6) were inoculated with M bovis, and euthanatized 12 hours later. Tears were collected from all calves that had been inoculated more than 24 hours earlier. The concentration of myeloperoxidase and collagenase was determined for each sample. After the calves were euthanatized, the corneas were dissected free, fixed, and examined by use of scanning or transmission electron microscopy, or light microscopy. Microscopic corneal erosions were detected 12 hours after inoculation. These lesions were not accompanied by inflammatory cell infiltration and were detected by use of scanning electron microscopy. Inflammatory cells were first observed in the corneal lesions in specimens collected 24 hours after inoculation. Bacteria that resembled M bovis morphologically were seen in several locations in these lesions. By 8 days, corneas of the group-I calves had the least number of intracorneal bacteria, compared with the corneas from other groups. The number of calves that developed corneal ulcers by 8 days was similar in all groups. The corneal ulcers of the hydroxyurea-treated calves were shallower, but appeared larger in surface area than those of the controls. By 8 days after inoculation, the corneal ulcers of the dexamethasone-treated calves had less corneal neovascularization and opacification than did the controls. Corneal perforations developed in 2 eyes of the dexamethasone-treated calves, but did not develop in any eyes of the controls. Microscopically, a larger number of M bovis were observed in corneas of dexamethasone-treated calves than in corneas of calves from other groups. Collagenase was not detected in any tear samples. The concentration of myeloperoxidase in tear samples were significantly (P less than 0.05) higher in the prehydroxyurea-treatment samples than in the posttreatment samples from corresponding calves.

Animals↗
PubMed1988

Enhancement of infectious bovine keratoconjunctivitis by modified-live infectious bovine rhinotracheitis virus vaccine.

The effects of a modified-live infectious bovine rhinotracheitis virus vaccine (administered ocularly or intranasally) on experimentally induced infectious bovine keratoconjunctivitis were evaluated. The modified-live infectious bovine rhinotracheitis virus vaccine was administered to 13 male Holstein calves (intranasally in 4 and ocularly in 9; day 0). Five calves were not vaccinated and served as controls. Calves were examined daily and, starting on day 4, Moraxella bovis was administered ocularly to all 18 calves once daily for 4 days. The eyes of all calves were assigned a clinical score, and the ocular secretions were evaluated for presence of infectious bovine rhinotracheitis virus and M bovis daily until day 19. The severity of the ocular lesions was estimated by scoring the lesions clinically and by determining the protein concentration, myeloperoxidase activity, and WBC count in the tears. By day 5, conjunctivitis, chemosis, and epiphora were observed in all of the calves vaccinated ocularly. The calves vaccinated intranasally developed conjunctival plaques, but did not develop chemosis or photophobia. All of the calves developed keratitis after inoculation with M bovis. The median lesion scores were greater in both groups of vaccinated calves than in the controls. Corneal perforations developed exclusively in the vaccinated calves. The frequency of M bovis isolation from ocular secretions was significantly (P less than 0.05) greater in the vaccinated calves than in the controls. The tears from the intranasally vaccinated calves contained the highest myeloperoxidase activity and WBC count. The mean protein concentration in the tears of vaccinated calves was not significantly different from that in tears of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Ormetoprim-sulfadimethoxine in cattle: pharmacokinetics, bioavailability, distribution to the tears, and in vitro activity against Moraxella bovis.

The pharmacokinetics, bioavailability, and distribution to the tears of ormetoprim (OMP; 5.5 mg/kg of body weight) and sulfadimethoxine (SDM; 27.5 mg/kg of body weight) were determined following IV or oral administration to 6 Holstein steers. After IV administration, the disposition kinetics of both drugs were best described by a 2-compartment open model. Sulfadimethoxine had a moderately rapid distribution phase, followed by a slower elimination phase, with a mean half-life (t 1/2) of 7.91 hours. The mean volume of distribution of SDM was 185 ml/kg, and the mean body clearance was 0.28 ml/min X kg. The concentration of SDM in tears was lower than the corresponding plasma concentration, and the elimination of SDM from tears (t 1/2 = 3.02 hours) was significantly faster than its elimination from plasma (t 1/2 = 7.91 hours). The disposition of OMP administered IV was characterized by a rapid distribution phase, followed by a rapid elimination phase (t 1/2 = 1.37 hours). The high values of the mean volume of distribution (1,450 ml/kg) and mean rate of body clearance (13.71 ml/min X kg) indicated that OMP was widely distributed in the body and was rapidly cleared from the body. Ormetoprim concentrations in tears exceeded corresponding plasma concentrations, and the elimination of OMP from tears was significantly slower (t 1/2 = 1.91 hours) than from plasma (t 1/2 = 1.37 hours). After oral administration of an OMP-SDM combination in bolus form, the absorption of SDM was slow (absorption t 1/2 = 3.32 hours), but complete.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1986

Distribution of kanamycin in ocular tissues of calves.

The ocular distribution of kanamycin following intramuscular, bulbar subconjunctival injection, or after constant rate intravenous infusion to calves was studied. Steady-state plasma concentrations of kanamycin were achieved in either normal calves, or in those experimentally infected with Moraxella bovis, and the concentrations of kanamycin in the serum, aqueous humor, vitreous body, tears, and the ocular tissues were measured. Kanamycin was not detected in the retina, lens, vitreous body, or the aqueous humor of any eyes, but the concentration of drug in the tears, conjunctiva, cornea and the orbital lacrimal gland of these calves ranged between 18 and 21% of that in serum. At steady-state plasma levels, the kanamycin concentrations in tears from eyes with keratoconjunctivitis and from normal eyes were similar. A study using lyophilized, powdered, ocular tissues in vitro showed that kanamycin was highly bound to the bovine retina and iris, and could be eluted using 0.2 N NaOH. The binding of kanamycin to other ocular tissues, including cornea, conjunctiva and lens, was significantly less. The concentration of kanamycin in the serum and the tears of calves was also measured after intramuscular or bulbar subconjunctival injection. After intramuscular administration of kanamycin (10 mg/kg of body-weight), the mean serum concentration was maximal at 1 h (32 micrograms/ml) and remained greater than or equal to 1.0 microgram/ml for 8 h. The mean tear concentration was maximal (3.1 micrograms/ml) at 30 min, and remained greater than or equal to 1.5 micrograms/ml for only 2.5 h. Following bulbar subjunctival administration of kanamycin (100 mg, single subconjunctival dose), the mean tear concentration was 1127 micrograms/ml at 30 min, less than or equal to 4.1 micrograms/ml at 4 h, and thereafter was less than or equal to 1.0 microgram/ml. It was concluded that kanamycin has limited distribution to the ocular tissues following parenteral administration. Binding of the drug to the ocular pigments may be responsible for its limited intraocular penetration.

Animals↗
PubMed1985

Distribution of oxytetracycline into ocular tissues and tears of calves.

A long-acting oxytetracycline formulation was administered (20 mg/kg of body weight) intramuscularly to calves, and the concentrations of the drug in serum, ocular tissues and tears were measured. The drug was distributed selectively to the epithelium of the conjunctiva and to the lacrimal gland ductules, and reached concentrations in each tissue that exceeded those in serum. The drug did not penetrate into the aqueous humour, and produced mean peak lacrimal fluid concentrations less than 1 microgram/ml after i.m. administration. When given subconjunctivally, however, concentrations greater than 2.0 micrograms/ml were observed in tears for 72 h. Severe local reactions occurred in all calves that were given the drug subconjunctivally.

Animals↗
PubMed1985

Treatment of Moraxella bovis infections in calves using a long-acting oxytetracycline formulation.

Studies were undertaken to determine the effectiveness of an oxytetracycline HCl formulation for the prophylaxis and treatment of chronic Moraxella bovis ocular infections in calves. Two separate experiments were performed. For the first, calves were separated into two groups and the eyes were infected with M. bovis. The eyes of these calves were observed and cultured for 37 consecutive days. On the 37th and 40th day, each of the five calves were treated intramuscularly with the drug (20 mg/kg of body weight). The other five calves (second group) remained untreated as controls. The cultures from the five treated calves were negative after the first antibiotic administration and remained so for 14 days. M. bovis was isolated from each eye of the control calves at least once during that time. None of the antibiotic-treated calves was completely resistant when reinfected with M. bovis. For the second experiment, calves were given a prophylactic administration of the formulation and were then infected with M. bovis 48 (n = 4 calves) or 72 (n = 4 calves) h later. These treatments resulted in a lower incidence of keratoconjunctivitis and a decreased duration of bacterial shedding, as compared to controls (n = 8 calves), but did not completely prevent the occurrence of disease or the establishment of ocular infections.

Animals↗
PubMed1985

Treatment of acute ocular Moraxella bovis infections in calves with a parenterally administered long-acting oxytetracycline formulation.

Acute ocular Moraxella bovis infections were induced in the UV-irradiated eyes of 10 calves. Eight calves developed corneal ulcers in at least 1 eye and were used for the treatment experiment. One randomly selected group of 4 calves with corneal ulcers and M bovis infections in 7 eyes was given a long-acting oxytetracycline formulation in 2 IM dosages of 20 mg/kg of body weight each, 72 hours apart. The other 4 calves with corneal ulcers in 6 eyes and M bovis in all 8 eyes served as nontreated controls. Bilateral ocular cultures were obtained and clinical observations were made daily for 20 days after treatment. After administration of the long-acting drug, new ulcers did not develop in the treated calves, whereas 5 new ulcers developed in the control-group calves during this time. The average durations of increased lacrimation/ulcerated eye were 2 and 12 days after treatment in the treatment and control groups, respectively; the average durations of blepharospasm were 3 and 8 days, respectively. Moraxella bovis was not isolated from any of the eyes of the treatment-group calves for the first 6 days after the antibiotic was administered, but was isolated from 1 eye of 1 treated calf on posttreatment day 7 and daily thereafter, for a total of 14 positive cultures of 160 ocular cultures obtained from the treatment-group calves after treatment. The bacterium was isolated from all eyes and from 144 of 160 cultures from the control-group calves during this time.

Animals↗
PubMed1982

Hemolytic anemia in horses after the ingestion of red maple leaves.

Signs of acute hemolytic anemia developed in 4 adult horses from 2 Georgia farms 3 to 4 days after the ingestion of wilted leaves from cut red maple trees (Acer rubrum). Clinical findings included weakness, polypnea, tachycardia, depression, icterus, cyanosis, and brownish discoloration of the blood and urine. Blood changes included methemoglobinemia, free plasma hemoglobin, decreased pcv, and Heinz bodies in erythrocytes. These findings plus hemoglobinuria suggested intravascular hemolysis. Three of the 4 horses diet 5 to 7 days after ingestion of the leaves. Gross pathologic changes included generalized icterus, splenomegaly and swollen, black kidneys. Microscopic changes including tubular nephrosis with hemoglobin casts, vacuolization of centrilobular hepatocytes, and sequestration of erythrocytes in splenic sinusoids. A disease indistinguishable from the field cases was induced in a pony by the oral administration of dried, ground red maple leaves at a dosage of 1.5 g/kg. The findings of methemoglobinemia, hemolysis, and Heinz bodies suggested that the toxic principle of the red maple leaf was an oxidant.

Anemia, Hemolytic↗
PubMed1982

Heinz body anemia and methemoglobinemia in ponies given red maple (acer rubrum L.) leaves.

Ponies given dried red maple (Acer rubrum L.) leaves at a dose of 3.0 gm/kg body weight became ill and died one to five days after administration of the leaves. Two clinical patterns of disease were seen. Ponies given dried leaves collected after September 15 died by 18 hours, while ponies given dried leaves collected before September 15 became ill with a hemolytic syndrome and died by three to five days. Freshly harvested leaves administered immediately after collection did not produce disease in ponies, but when dried, they became toxic and remained so for at least 30 days. Overnight freezing did not alter the toxicity of the leaves. Leaves were toxic when administered at doses of 1.5 gm/kg of body weight. The clinical signs of ponies with the hemolytic syndrome included polypnea, tachycardia, icterus, cyanosis, scleral petechiation, and brownish discoloration of the urine and blood. Blood changes of ponies with the hemolytic syndrome included anemia, hemoglobinemia, Heinz bodies, depletion of erythrocyte reduced glutathione, increased erythrocyte fragility, and increased serum levels of aspartate amino transferase, sorbitol dehydrogenase, plasma protein, and bilirubin. Lesions of ponies that died from the hemolytic syndrome included icterus, centrilobular hepatic degeneration, hemoglobinemic nephrosis, and erythrophagocytosis by splenic, adrenal, and hepatic phagocytes. Only brownish discoloration of the blood and mild centrilobular hepatic degeneration were observed in the four ponies that died peracutely.

Anemia, Hemolytic↗
PubMed1981

Chronic respiratory disease in a horse infected with Dictyocaulus arnfieldi.

A 6-year-old Thoroughbred gelding was examined because of respiratory disease that developed after it was placed on pasture occupied by a donkey. Clinical signs in the gelding included a harsh, dry paroxysmal cough and increased expiratory effort. Eosinophils were seen in smears of mucus aspirated from the trachea and the bronchi. Immature, 5th-stage Dictyocaulus arnfieldi was identified in the tracheal mucus. The cough and other clinical signs were not diminished by corticosteroid therapy or by the administration of bronchodilators. Treatment with 10-fold therapeutic dosages of thiabendazole (440 mg/kg) on each of 2 successive days resulted in permanent cessation of the clinical signs.

Animals↗
PubMed1981

Brainstem auditory evoked response in the diagnosis of inner ear injury in the horse.

Brainstem auditory evoked response (BAER) testing was done to evaluate inner ear/VIIIth cranial nerve (CN8) function in the horse. The BAER test consisted of stimulating the auditory system with clicks and recording far-field responses of the brainstem auditory components via cutaneous electrodes and a signal averaging system. The normal response was shown to be a series of waves occurring within the first 10 msec after the stimulus click. Functional loss of the auditory receptor organ (cochlea) or CN8 results in loss of the entire response on the side of the injury. Because of the anatomic relationships of the peripheral auditory and vestibular systems, trauma to one will injure the other. Therefore, auditory testing (BAER tests) may be used to advantage in the diagnosis of peripheral vestibular disease. The BAER test was used in a horse that had signs suggestive of vestibular dysfunction or a brain lesion. The test helped to demonstrate a unilateral inner ear/CN8 lesion and to discount the probability of a more central lesion.

Animals↗
PubMed1980

Effects of dietary aflatoxin on performance and zinc metabolism in dairy calves.

Young dairy calves were fed diets containing 40 or 640 ppm zinc with 0 or 5 ppm aflatoxin for 3 wk. The aflatoxin mixture contained 80.5% B1, 19.5% G1, and less than .1% B2 and G2. The aflatoxin-fed calves exhibited characteristic signs of aflatoxicosis which included reduced feed intake, weight gains, nitrogen balance, pulse rate, and respiration rate. Feed intake and weight gains recovered some during the 3rd wk. No gross abnormalities were observed in the liver or other organs at autopsy. Addition of 600 ppm zinc to diets containing aflatoxin did not alleviate the toxic conditions. Effects of aflatoxin or zinc metabolism were investigated during the 3rd week of treatment through oral dosing of zinc-65. Absorption of zinc-65 was slightly lower in aflatoxin-fed calves. However, the aflatoxin effect on absorption of zinc-65 was less than that of high dietary zinc. Retention of zinc-65 in small intestinal tissue was increased in aflatoxin-fed calves, but concentrations in other tissues were not affected. Stable zinc was reduced in liver and increased in kidney and three sections of the small intestine. Further research is needed to define more clearly the relationship of zinc to aflatoxin in dairy calves.

Aflatoxins↗