Canine erythrocytes were loaded with the antineoplastic drug doxorubicin and then treated with 0.16% glutaraldehyde. This procedure has been previously shown to slow down the efflux of doxorubicin from erythrocytes and to result in the selective targeting of the carrier erythrocytes to liver. Three dogs were treated each with 2 different schedules of IV bolus administration of doxorubicin (0.4 mg/kg of body weight): free drug and doxorubicin encapsulated in glutaraldehyde-treated erythrocytes. The 2 treatments yielded consistent differences in the plasma pharmacokinetic properties of doxorubicin and of its only metabolite, doxorubicinol. A triphasic exponential decay of doxorubicin plasma concentrations was observed on injection of the free drug. Conversely, in the case of erythrocyte-encapsulated doxorubicin, 4 phases of plasma concentrations of doxorubicin were found. The plasma concentrations of doxorubicinol, after a steady increase during the first hour, followed patterns of decay comparable to those of the parent drug. On the basis of the kinetic variables calculated with the 2 administration schedules, area under curve concentrations of plasma doxorubicin were 136 microgram.h/L (free infusion) and 734 microgram.h/L erythrocyte-encapsulated drug). Significant alterations of hematologic and hematochemical factors were not observed in the 3 dogs during and after the 2 treatments. On the basis of our findings, doxorubicin-loaded and glutaraldehyde-treated erythrocytes may potentially be used in the treatment of systemic and hepatic tumors in dogs.

Pathophysiologic effects of Ostertagia ostertagi infection and their prevention by strategic anthelmintic treatments were studied in 3 groups each of 6 steer calves. Group-1 calves were noninfected controls. Group-2 calves were inoculated with 100,000 third-stage larvae on the 1st and 28th days of the experiment and grazed on pasture initially free of contamination. Group-3 calves were on a similar regimen as those in group 2, but were also treated with ivermectin 9 days after each larval inoculation. Group-2 calves had increased plasma pepsinogen and gastrin values and decreased weight gains, and total serum protein and albumin concentrations from the 2nd week of infection onward. They were anemic at 10 to 12 weeks and had lower carcass and meat quality at slaughter. Strategic anthelmintic treatments were effective in preventing these effects and calves in groups 1 and 3 had similar performances. On the basis of our findings, high pepsinogen values were related to worm burdens, whereas high gastrin concentrations were related to gastric lesions.

Eight of 10 pony foals reared under helminth-free conditions were inoculated PO with 50 Strongylus vulgaris infective larvae/week for 4 weeks, at which time 1 foal died of acute verminous arteritis. Inoculation of 7 remaining foals continued at 2-week intervals for 20 weeks. Of the 7 foals, 3 were treated with ivermectin (0.2 mg/kg of body weight) in an oral paste formulation at experiment weeks 8, 16, 24; 4 foals were not treated. Two foals were not inoculated or treated and served as controls. After the first ivermectin treatment, ivermectin-treated foals had fewer days (12 +/- 2.9) with rectal temperatures > 38.6 C than did nontreated foals (23.3 +/- 3.8). Mean baseline rectal temperatures were 38 +/- 0.2 C. Adverse clinical reactions to ivermectin treatment were not observed in foals. Foals were euthanatized and necropsied 3 weeks after the last ivermectin treatment (week 24). Ivermectin was effective in reducing S vulgaris arterial larval and intestinal adult parasite numbers by 100% in 3 treated foals. Strongylus vulgaris arterial larvae and/or adults were recovered from all 4 nontreated inoculated foals. One nontreated inoculated foal lacked arterial larvae or active arterial lesions, indicating that protective resistance had developed in this individual. Marked gross and histopathologic lesions typical of chronic S vulgaris infection were observed in the 3 nontreated inoculated foals with arterial larvae. Repeated killing of intra-arterial S vulgaris fourth-stage larvae in ivermectin-treated foals did not exacerbate lesions associated with verminous arteritis or induce unique lesions associated with repeated destruction of arterial larvae. Arterial lesions in treated inoculated foals were markedly reduced and had resolved, compared with those in nontreated inoculated foals.

Ceftiofur hydrochloride was tested for effectiveness against induced colibacillosis in neonatal swine. In this model, pigs < 12 hours old were inoculated via stomach tube with a virulent, K99+, nalidixic acid-resistant strain of Escherichia coli. Six hours after challenge exposure, 1 dose of ceftiofur was administered either IM or orally in experiment 1 and orally only in experiment 2. Mortality, shedding of bacteria, fecal consistency scores, and body weight changes were monitored for 10 days. In experiment 1 (n = 383 pigs), all treatments at dosage that ranged between 0.5 and 64.0 mg of ceftiofur/kg of body weight significantly (P < 0.001) reduced mortality, bacterial shedding, and diarrhea and increased weight gain, compared with findings in untreated controls. There were no detectable differences between oral and IM routes, except that there was greater reduction in bacteria shedding associated with the oral route of administration. In experiment 2 (n = 505 pigs), ceftiofur was administered orally either once at 6 hours after challenge exposure or twice at 6 and at 48 hours after the first dose. Dosage of ceftiofur was 0, 5, 10, 20, 30, or 60 mg/kg administered once, or half the same dose was administered at each of 2 times. At the optimal dosage (10 mg/kg), a single dose was as effective as 2 doses. The single administration at all dosages reduced mortality, bacterial shedding, and diarrhea scores and increased body weight gain, compared with findings in untreated pigs (P < 0.01). In this induced infection model, the optimal treatment dosage was determined to be 10 mg/kg administered once.

Canine gastric dilatation-volvulus (GDV) is a naturally acquired condition of large-breed dogs primarily and is associated with high mortality. The clinical course suggests that reperfusion injury may be important in the pathogenesis of GDV. To evaluate the role of xanthine oxidase and iron-dependent lipid peroxidation (which are purported mechanisms of reperfusion injury) in the pathogenesis of GDV-related mortality, we created experimental GDV in 21 dogs. These dogs were then treated with either allopurinol (a xanthine oxidase inhibitor), U74006F (an experimental lipid peroxidation inhibitor), or saline solution (NaCl, 0.85%). Three of 8 dogs died in the allopurinol-treated group, none of 5 died in the U74006F-treated group, and 4 of 8 died in the saline solution-treated group. Tissue malondialdehyde concentration, a nonspecific indicator of lipid peroxidation, was significantly (P < 0.05) greater in the duodenum, jejunum, colon, liver, and pancreas of the saline-solution treated and allopurinol-treated dogs than in the same tissues of the U74006F-treated dogs after surgical correction of the GDV (ie, during reperfusion), compared with malondialdehyde concentrations determined before inducing GDV. The results of this study support the concept that lipid peroxidation associated with reperfusion injury is important in the pathogenesis and high mortality of canine GDV. Furthermore, this lipid peroxidation and mortality may be preventable by appropriate and timely treatment.

Streptococcal species isolated from dairy cows with clinical mastitis were obtained from mastitis research workers in Florida, Louisiana, New York, Vermont, Washington, and West Virginia. Seventy-one streptococcal isolates were tested, including 39 strains of Streptococcus agalactiae, 21 strains of S dysgalactiae, and 11 strains of S uberis. The minimal inhibitory concentration of erythromycin, lincomycin, oxytetracycline, penicillin, spectinomycin, streptomycin, and tetracycline was determined for each isolate. Differences were not detected among strains with respect to geographic origin. None of the strains was resistant to penicillin. Lincomycin was the next most effective antimicrobial, with only 2 resistant strains of each streptococcal species. There were no differences among the streptococcal species with respect to resistance to either penicillin or lincomycin. Streptococcus uberis was more likely to be resistant to erythromycin than were S agalactiae and S dysgalactiae (P < 0.02). Streptococcus agalactiae and S uberis had similar distributions for resistance to oxytetracycline, tetracycline, spectinomycin, and streptomycin. Strains of S dysgalactiae were more likely to have intermediate resistance to oxytetracycline and streptomycin than were strains of S agalactiae and S uberis, which were highly resistant to oxytetracycline and streptomycin (P < 0.001). Differences were not detected among the streptococcal species with respect to resistance to spectinomycin. Resistance to multiple antimicrobials was observed in all streptococcal species tested. Although S dysgalactiae appeared to have a greater percentage of strains (73%) that were resistant to multiple antimicrobials than did S agalactiae (31%) or S uberis (45%), differences were not statistically significant.

The in vitro antimicrobial activities of aditoprim (AP), a new dihydrofolate reductase (DHFR) inhibitor, trimethoprim (TMP), sulfadimethoxine (SDM), sulfamethoxazole (SMX), and combinations of these drugs against some porcine respiratory tract pathogens were determined by use of an agar dilution method. The minimal inhibitory concentrations (MIC) of these agents were determined twice against Bordetella bronchiseptica (n = 10), Pasteurella multocida (n = 10), and Actinobacillus pleuropneumoniae (n = 20) strains isolated from pigs suffering from atrophic rhinitis or pleuropneumonia. All B bronchiseptica strains were resistant to AP and TMP. The MIC50 values of AP and TMP for P multocida were 0.25 and 0.06 microgram/ml, respectively, and for A pleuropneumoniae, 1 and 0.25 microgram/ml, respectively. The MIC50, values of SDM and SDM for B bronchiseptica were 4 and 1 microgram/ml, respectively; for P multocida, 16 and 8 microgram/ml, respectively; and for A pleuropneumoniae, 16 and 8 microgram/ml, respectively. The investigated combinations of the DHFR inhibitors and the selected sulfonamides had synergism for the A pleuropneumoniae strains; the MIC90 values of the combinations were less than or equal to 0.06 microgram/ml. Potentiation was not observed for the B bronchiseptica and the P multocida isolates. The MIC of the combinations against B bronchiseptica and P multocida corresponded respectively to the concentrations of the sulfonamides and the DHFR inhibitors in the combinations. For A pleuropneumoniae, 2 types of strains were used (25% of serotype 2 and 75% of serotype 9). Type-2 strains had lower susceptibility than type-9 strains to AP and TMP as well as to SDM and SMX (at least a fourfold difference in MIC between the 2 types of strains). The MIC of the combinations were similar for the 2 types of strains.

Hemodynamic effects of spontaneous ventilation, intermittent positive-pressure ventilation (IPPV), and high-frequency oscillatory ventilation (HFOV) were compared in 6 dogs during halothane anesthesia. Anesthesia was induced with IV thiamylal Na and was maintained with halothane (end-tidal concentration, 1.09%). During placement of catheters, dogs breathed spontaneously through a conventional semiclosed anesthesia circuit. Data were collected, and dogs were mechanically ventilated, using IPPV or HFOV in random order. Ventilation was adjusted to maintain PaCO2 between 38 and 43 mm of Hg during IPPV and HFOV. Cardiac index, aortic blood pressure, and maximum rate of increase of left ventricular pressure were significantly (P less than 0.05) less during HFOV than during spontaneous ventilation, whereas right atrial and pulmonary artery pressure were significantly greater during HFOV than during spontaneous ventilation. During IPPV, only the maximum rate of increase of left ventricular pressure was significantly less than that during spontaneous ventilation.