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Biomedical subjects

H D Knight

Publications and source records attributed to H D Knight.

At least 19 recordsLinked to original sources
PubMed1988

Pyrrolizidine alkaloid-induced liver disease in horses: an early diagnosis.

Nine adult horses were fed alfalfa hay cubes containing approximately 10% Senecio vulgaris until all horses had consumed approximately the same amount of toxic components of S vulgaris, pyrrolizidine alkaloids (PA). The amount of PA consumed was determined by the amount that induced clinical signs of PA toxicosis in 3 horses. The 6 other horses were given similar amounts per kilogram of body weight. An initial decrease of feed intake was observed when horses' diets were changed from alfalfa cubes to alfalfa/Senecio cubes, and feed intake was decreased further over 89 to 98 days. From 50 to 159 days, body weight decreased in all horses. Liver disease was induced in all 9 horses after they ate an average of 233 +/- 9.2 mg of PA/kg of body weight. Eight horses died or were euthanatized. Treatment with branched chain amino acids had no effect on mortality, but appeared to reduce neurologic problems. Clinical signs of PA-induced liver disease included ataxia, head pressing, and decreased feed intake. Other clinical signs of toxicosis were observed individual horses, but did not develop in most horses. Megalocytic hepatopathy developed. Liver abnormalities proceeded as PA was consumed and were severe in 8 of 9 horses before clinical signs of toxicosis appeared. Sulfobromophthalein sodium clearance did not decrease until PA-induced liver disease was advanced. Bile acid (BA) concentrations increased to greater than or equal to 50 mumol/L, in the 8 horses that died. One horse had hepatopathy and increased BA concentration, but survived. In this horse, BA concentration peaked at 33 mumol/L and then decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids, Branched-Chain↗
PubMed1983

Pharmacokinetics of chloramphenicol in the neonatal horse.

Chloramphenicol sodium succinate was administered as an intravenous bolus (50 mg/kg) to eight foals which weighed 49-57 kg (mean +/- 1 standard deviation = 53.19 +/- 2.66) each, and were 1-9 days (4.5 +/- 2.56) of age. The drug was rapidly distributed and followed first-order elimination. Mean pharmacokinetic values were: zero-time serum concentration (C0) = 36.14 microgram/ml (+/- 14.80); apparent specific volume of distribution (Vd) = 1.614 1/kg (+/- 0.669); and elimination rate constant (K) = 0.7295 h-1 (+/- 0.3066) which corresponds to a biological half-life (t1/2) = 0.95 h. These values do not differ greatly from those reported for adult horses and ponies. A suspension of chloramphenicol was administered by nasogastric tube (50 mg/kg) to a second group of seven foals which weighed 49 to 57 kg (51.34 +/- 2.82) each and were 1 to 7 days (4.43 +/- 1.90) of age. A mean peak serum chloramphenicol concentration of 23.97 microgram/ml (+/- 7.06) was achieved 1.14 h (+/- 0.63) after administration. The bioavailability of this preparation was 83.27 percent.

Animals↗
PubMed1981

Oxytetracycline hydrochloride in the horse: serum, synovial, peritoneal and urine concentrations after single dose intravenous administration.

Six adult mares were given a single intravenous injection of oxytetracycline HCl (50 mg/ml) at a dosage of 5 mg/kg. Serum, synovial fluid, peritoneal fluid, and urine oxytetracycline concentrations were measured serially over a 48-h period. The highest measured serum oxytetracycline concentration was 8.01 mcg/ml at 1/2 h. Oxytetracycline was detected in synovial fluid and peritoneal fluid, which obtained mean peak oxytetracycline concentrations of 4.43 mcg/ml and 4.20 mcg/ml, at 1/2 h and 1 h, respectively. These concentrations steadily declined in parallel with serum concentrations and were not measurable at 48 h. Urine oxytetracycline concentration was relatively high, with a peak concentration of 1565.2 mcg/ml at 1/2 h after drug administration.

Animals↗
PubMed1981

Aqueous procaine penicillin G in the horse: serum, synovial, peritoneal, and urine concentrations after single-dose intramuscular administration.

Six adult mares were given a single dose of aqueous suspension procaine penicillin G (300,000 IU/ml) IM at a dosage of 22,000 IU/kg of body weight (15.4 mg of penicillin G/kg). Serum, synovial fluid, peritoneal fluid, and urine penicillin concentrations were measured serially over a 48-hour period. The mean peak serum penicillin concentration was 1.42 microgram/ml at 3 hours. Penicillin was detected in synovial fluid and peritoneal fluid, which obtained mean peak penicillin concentrations of 0.62 microgram/ml and 0.58 microgram/ml, at 4 hours and 3 hours, respectively. These concentrations steadily decreased in parallel with serum concentrations and were still measurable at 48 hours. Urine concentrations of penicillin were relatively high, with a mean peak concentration of 525.81 microgram/ml at 8 hours.

Animals↗
PubMed1978

California goats with a disease resembling enzootic ataxia or swayback.

In a retrospective study typical signs and lesions of enzootic ataxia or swayback were found in 16 young dairy goats from eight widely scattered herds in California. In addition to the constant appearance of chromatolytic neurons in brainstem and spinal cord, and myelin deficiency in certain tracts of the cord, cerebellar hypoplasia was found frequently. Liver copper was subnormal in six of nine kids tested. The disease is viewed as a developmental defect in which failure of neuronal perikaryon metabolism leads to distal axonopathy with secondary demyelination.

Animals↗
PubMed1978

A serologic method for the detection of Corynebacterium pseudotuberculosis infections in horses.

A serologic technique useful for detecting antibodies formed in horses in response to infection with Corynebacterium pseudotuberculosis is described. The test relies on the ability of C. pseudotuberculosis toxin to produce a wide zone of hemolysis when applied to erythrocytes previously treated with a sterile filtrate of Corynebacterium equi broth culture. The synergistic hemolytic activity can be neutralized by anti-C. pseudotuberculosis serum. This test was used to analyze sera from 616 horses for the presence of C. pseudotuberculosis antitoxin. Of 177 animals (see Table 2) found positive, there were 34 horses with bacteriologically confirmed, active infections and 18 with active but unconfirmed infections. In addition, 13 animals had a history of having had the disease and 112 had no history or evidence of having had the infection. The other 439 horses had negative titers. Statistical treatments confirmed the value of the test as an epidemiological tool but precluded using only titers for the diagnosis of active clinical disease.

Animals↗
PubMed1977

Bromide intoxication of horses, goats, and cattle.

During the summer and fall of 1973, a few horses, goats, and cattle in the Napa Valley of California became intoxicated by bromide via the ingestion of volunteer oat hay that had been cut from a field treated with methyl bromide, a soil fumigant. The bromide content of the hay ranged from 6,00 to 8,400 ppm. Signs of intoxication were lethargy, weakness, and ataxia. Animals experimentally fed the contaminated hay developed signs of intoxication between the 7th and 9th days.

Animal Feed↗
PubMed1977

Intoxication of cattle with sodium bromide-contaminated feed.

Five concentrations of bromide ion, sodium bromide, were incorporated into a pelleted ration and fed to 5 groups of cattle for 49 days. Another group of cattle was fed volunteer oat hay cut from a field that had been fumigated with methyl bromide. On analysis, the hay contained between 6,800 and 8,400 parts per million of bromide ion. Groups fed the pelleted ration containing the highest concentration of bromide and those eating the contaminated hay developed signs of motor incoordination between the 10th and 12th days. The sign of incoordination correlated with serum bromide concentrations of 30 mEq/L or more. Serum bromide concentrations and associated neurologic signs subsided markedly 14 days after feeding of the toxic feeds was discontinued.

Animal Feed↗
PubMed1976

Effects of vaccination infectious bovine rhinotracheitis and simultaneous administration of levamisole on primary humoral responses in calves.

In a study on the primary humoral response of calves vaccinated against infectious bovine rhinotracheitis (IBR) and simultaneously given levamisole, mild but consistent suppression of the group's geometric mean serum-neutralization titer to IBR virus occurred between 12 and 59 days later. The quantitative determination of circulating immunoglobulins (Ig) over the same period indicated a slight decrease in the IgG concentrations from an initial geometric mean concentration of 18.28 mg/ml before calves were vaccinated to 15.29 mg/ml after vaccination, and the control calves (vaccinated and given saline solution only) maintained their prevaccination IgG geometric mean concentration of 20.92 mg/ml. Difference was not observed in the circulating IgM values of the 2 groups. Levamisole had no apparent effect on the circulating Ig-bearing lymphocyte values when compared with control calves during the 24 hours of treatment. It was concluded that a single treatment of levamisole may mildly suppress the primary humoral response to IBR vaccination in calves, but it is unlikely that this would affect the animal's capability to recover from, or maintain resistance to, IBR infection.

Animals↗
PubMed1975

Enhanced resistance to Corynebacterium pseudotuberculosis infections associated with reduced serum immunoglobulin levels in levamisole-treated mice.

The effect of levamisole (1-2,3,5,6-tetrahydro-6-imidazo[2,1-b]thiazole monohydrochloride) treatment on the course of a Corynebacterium pseudotuberculosis infection and the ability of either vaccinated or unvaccinated randomly bred mice to resist challenge were investigated. It was found that either a double treatment of levamisole administered with or without a sublethal inoculation of C. pseudotuberculosis or a single treatment of levamisole alone had a significant effect on the ability of mice to resist challenge with virulent C. pseudotuberculosis. This prolonged, enhanced nonspecific and specific resistance was associated with a quantitative reduction in the geometric mean serum immunoglobulin levels, with the immunoglobulin G2 and immunoglobulin A levels being more severely affected. As the enhanced nonspecific resistance to C. pseudotuberculosis was associated with depressed serum immunoglobulin levels in the mice pretreated with levamisole alone, it was suggested that the cell-mediated immunity may play a more important role than the humoral immunity in the resistance to C. pseudotuberculosis infection.

Animals↗
PubMed1975

Pathogenicity of a caprine herpesvirus.

A herpesvirus isolated from neonatal Angora kids (Capra hircus) with a relatively severe generalized infection was shown to be infective for adult goats as well as for kids. However, the virus lacked pathogenicity for either lambs or calves. Although a nonreciprocating serologic overlap exists between the caprine virus and the antibody to bovine herpesvirus (BHV-1), results of cross immunity tests in calves indicated that the 2 viruses are immunologically distinct. On the basis of these findings, the caprine virus seems to be a specific pathogen of goats. Accordingly, the designation of Herpesvirus caprae or caprine herpesvirus 1 seems taxonomically appropriate.

Abortion, Veterinary↗