Molecular techniques previously used for genome comparisons of closely related bacterial species could prove extremely valuable for comparisons of complex microbial communities, or metagenomes. Our study aimed to determine the breadth and value of suppressive subtractive hybridization (SSH) in a pilot-scale analysis of metagenomic DNA from communities of microorganisms in the rumen. Suppressive subtractive hybridization was performed using total genomic DNA isolated from rumen fluid samples of two hay-fed steers, arbitrarily designated as tester or driver. Ninety-six subtraction DNA fragments from the tester metagenome were amplified, cloned and the DNA sequences were determined. Verification of the isolation of DNA fragments unique to the tester metagenome was accomplished through dot blot and Southern blot hybridizations. Tester-specific SSH fragments were found in 95 of 96 randomly selected clones. DNA sequences of subtraction fragments were analysed by computer assisted DNA and amino acid comparisons. Putative translations of 26 (32.1%) subtractive hybridization fragments exhibited significant similarity to Bacterial proteins, whereas 15 (18.5%) distinctive subtracted fragments had significant similarity to proteins from Archaea. The remainder of the subtractive hybridization fragments displayed no similarity to GenBank sequences. This metagenomic approach has exposed an unexpectedly large difference in Archaeal community structure between the rumen microbial populations of two steers fed identical diets and housed together. 16S rRNA dot blot hybridizations revealed similar proportions of Bacteria and Archaea in both rumen samples and suggest that the differences uncovered by SSH are the result of varying community structural composition. Our study demonstrates a novel approach to comparative analyses of environmental microbial communities through the use of SSH.

Fenbendazole was administered orally without food to six beagle dogs at 2.5, 5.0, 10, 20, 40 and 80 mg/kg of body weight. Increasing the dose rate did not significantly increase the amount of fenbendazole absorbed. In a separate study fenbendazole was administered to the same six beagle dogs at a dose rate of 20 mg/kg of bodyweight in food with high, medium and low fat content. The food provided 1.52, 0.70 or 0.34 g of fat per kg of body weight. Administration of fenbendazole in food with different fat contents did not affect its relative bioavailability. Administration of fenbendazole at a dose rate of 20 mg/kg in food, irrespective of fat content, did however significantly increase its bioavailability when compared to administration of the same dose as a bolus on an empty stomach.

Fenbendazole was administered to dogs at a dose rate of 20 mg/kg body weight on a single occasion in gelatin capsules, on 5 consecutive days in feed, and on a single occasion as an alginate suspension. It was also administered at a dose rate of 100 mg/kg body weight on a single occasion in feed. Following single administration of 20 mg/kg fenbendazole mean maximum concentrations (Cmax) of the parent drug and its known active sulphoxide metabolite were 0.42 +/- 0.05 and 0.31 +/- 0.05 microgram/ml, respectively. Mean times until maximum concentrations were achieved (tmax) were 12.67 +/- 4.18 and 15.33 +/- 2.81 h, respectively, and areas under the plasma concentration-time curves (AUC) were 5.83 +/- 0.65 and 4.60 +/- 0.57 microgram.h/ml, respectively. Administration in feed increased the apparent bioavailability and administration for 5 consecutive days provided sustained plasma concentrations, generally greater than 0.2 microgram/ml. Administration as an alginate did not increase bioavailability or extend the persistence in plasma. It did increase the tmax to 16.80 +/- 2.93 and 20.00 +/- 2.53 h for fenbendazole and its sulphoxide metabolite, respectively. Increasing the dose from 20 mg/kg to 100 mg/kg did not substantially increase the Cmax or AUC.

When 400 micrograms ivermectin/kg was administered subcutaneously to rabbits infected with the ear mite Psoroptes cuniculi it significantly reduced the clinical score, and when 500 micrograms ivermectin/kg was administered subcutaneously to guinea pigs with mange due to Trixacaurus caviae it resulted in a clinical cure. In rabbits a subcutaneous dose of 400 micrograms/kg produced high and sustained concentrations of ivermectin in the tissues and body fluids for at least 13 days and its rate of depletion from tissues was similar to that observed in sheep and rats. The mean (+/- sem) maximum concentration in plasma was 42.0 +/- 9.7 ng/ml 37.2 +/- 5.0 hours after administration and the area under the concentration-time curve was 3543 +/- 580 ng/ml hours. After the administration of 500 micrograms ivermectin/kg to guinea pigs orally, subcutaneously or topically the drug could be detected in the plasma only after subcutaneous administration. The mean concentration 72 hours after its administration to four guinea pigs was 0.7 +/- 0.3 ng/ml.

No abstract