A monoclonal antibody (MAB) against equine tumor necrosis factor-alpha (Eq TNF) was used to investigate the role of TNF in cytokine, eicosanoid, and metabolic responses of Miniature Horses given endotoxin. Plasma concentrations of interleukin 6 (IL-6), lactate, thromboxane A2 metabolite, and prostacyclin metabolite (6-keto-PGF(1 alpha)) were measured in 10 Miniature Horses given 0.25 micrograms of lipopolysaccharide (LPS; Escherichia coli O55:B5)/kg of body weight. Five horses were given Eq TNF MAB and 5 were given isotype-matched MAB as control. All horses were given 1.86 mg of antibody/kg by IV infusion, 5 minutes before LPS was given IV. Blood samples were taken 20 minutes before and at multiple intervals for 24 hours after LPS was given. Interleukin 6 bioactivity in plasma was measured, using IL-6-dependent cell line (B9). Eicosanoid activities were assessed by enzyme immunoassay, and plasma lactate concentration was determined enzymatically. Data were analyzed by ANOVA and Tukey's honest significant difference test for significant (P < 0.05) effect of treatment. Horses given Eq TNF MAB had significantly (P < 0.050) lower peak mean +/- SEM IL-6 (59 +/- 29 U/ml), lactate (16 +/- 2.00 mg/dl), and 6-keto-PGF(1 alpha) (254 +/- 79 pg/ml) values then did horses given control MAB (880 +/- 375 U/ml for IL-6; 26 +/- 0.04 mg/dl for lactate; and 985 +/- 290 pg/ml for 6-keto-PGF(1 alpha)). There was no effect of anti-TNF treatment on LPS-induced thromboxane A2 metabolite production. Tumor necrosis factor mediated IL-6, lactate, and prostacyclin responses, without affecting thromboxane production in horses given LPS.

The effects of dexamethasone (0.2 mg/kg of body weight; IV, IM, and PO) and methylprednisolone acetate (120 mg, given intra-articularly) on serum osteocalcin and cortisol concentrations were studied in 6 horses. Serum osteocalcin and cortisol concentrations were serially monitored after each treatment. A significant (P < 0.05) decrease in serum osteocalcin and cortisol concentrations was observed from 12 to 24 and 2 to 48 hours, respectively, after IV and IM administrations of dexamethasone. Serum osteocalcin and cortisol concentrations were significantly decreased from 6 to 48 and 3 to 72 hours, respectively, after oral administration. In contrast, a change in serum osteocalcin concentration was not detected after intra-articular administration of methylprednisolone. Oral, IV, or IM treatment with 0.2 mg of dexamethasone/kg caused a decrease in serum osteocalcin concentration in horses.

Bacampicillin hydrochloride is an ester prodrug that is hydrolyzed to ampicillin after its absorption from the gastrointestinal tract. It was administered intragastrically at a dose rate of 13.5 mg/kg of body weight to ponies and horses, and was highly bioavailable (F = 41.0%), compared with other penicillins in adult horses. The high peak ampicillin plasma concentration of 6.1 +/- 0.5 micrograms/ml achieved and persistence of the antibiotic at concentration of 0.3 +/- 0.1 micrograms/ml 6 hours after its intragastric administration, suggest that bacampicillin hydrochloride may reach suitable bactericidal concentrations for treatment of infections caused by susceptible microorganisms. In a separate experiment, dichlorvos, an organophosphate compound that inhibits some of the esterase activity in plasma, was administered orally to the same animals at a dose rate of 40 mg/kg followed by intragastric administration of bacampicillin hydrochloride at a dose of 13.5 mg/kg. Plasma pseudocholinesterase and erythrocyte acetylcholinesterase activities were reduced to < 5% of reference (predichlorvos) values after dichlorvos administration. However, rate of hydrolysis of bacampicillin into ampicillin was not affected. Consequently, the disposition and fate of bacampicillin when administered intragastrically 1 day after dichlorvos administration were similar to the values obtained after administration of bacampicillin alone. Intragastric coadministration of probenecid at a dose rate of 75 mg/kg and bacampicillin at 13.5 mg/kg limited absorption of the antibiotic from the gastrointestinal tract. This suggests existence of a common transport mechanism for bacampicillin and probenecid in the gastrointestinal wall, and precludes use of this combination for treatment. The bioavailable fraction of ampicillin after combination treatment indicated prolonged residence time in the plasma, presumably as a consequence of reduced renal tubular secretion.

A method was developed to evaluate frequent milking as a means of controlling intramammary infection. An artificial intramammary environment was used to determine growth responses of Escherichia coli (P4) to natural changes in the mammary gland resulting from bacterial invasion. Physical conditions manipulated in this model were growth medium, temperature, and oxygen tension. Mathematical modeling was then incorporated to generate predictions concerning growth dynamics of the organism when milking frequency was changed. To test accuracy of the model, initial predictions were derived from bacterial growth data in which E coli was incubated in tryptose soy broth for 12 hours at 37 C and PO2 equal to 23.3 mm of Hg. These predictions matched closely with experimental data in which 12-, 4-, and 2-hour milking intervals were simulated in the artificial intramammary environment. The mathematical model was then used to characterize growth rate data from in vitro experiments in ultra-high temperature-treated milk and in vivo experimental infection data generated with E coli (P4). Predictions generated from this model suggested that increasing milking frequency to 4 or 6 times daily controls growth of E coli for a prolonged period and that 12 times daily milking may lead to elimination of the bacterium.

Tumor necrosis factor-alpha (TNF) is an important mediator of endotoxin-induced pathologic changes. To help define the role of TNF in equids with endotoxemia, the effects of pretreatment with a murine monoclonal antibody (MAB) against equine TNF were evaluated in Miniature Horses given endotoxin. Five horses were given TNF MAB at a dosage of 1.86 mg/kg of body weight, IV, and 5 were given control MAB. Five minutes later, lipopolysaccharide (LPS; Escherichia coli O55:B5), 0.25 micrograms/kg, was given to all horses by bolus IV infusion. Clinical signs of disease were monitored at intervals up to 24 hours after LPS infusion, and blood was taken for determination of WBC count, PCV, plasma total protein concentration, plasma TNF activity, and serum MAB concentration. Reduction of plasma TNF activity in anti-TNF-treated horses was highly significant (P < 0.001), compared with that in control horses. Horses given TNF MAB had significantly improved clinical abnormality score (P < 0.010), lower heart rate (P < 0.001), and higher WBC count (P < 0.001), compared with horses given control MAB. Rectal temperature, respiratory rate, PCV, and plasma total protein concentration were not significantly different between groups. Serum MAB concentration peaked at 68 micrograms/ml 30 minutes after the end of antibody infusion in both groups. Neutralization of LPS-induced TNF activity reduced the hematologic and clinical responses of horses given LPS IV.