In vivo effect of ascorbic acid on neutrophil function in healthy and dexamethasone-treated cattle

Ascorbic acid (20 mg/kg of body weight) administered subcutaneously to otherwise nontreated cattle resulted in enhancement of neutrophil oxidative metabolism and capability of neutrophils to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). Random migration, bacterial ingestion, and iodination by neutrophils was unaffected. Three dosage levels of ascorbic acid (10 mg/kg, 20 mg/kg, and 40 mg/kg) were examined for their effects on neutrophil function in cattle treated with dexamethasone (0.04 mg/kg). Dexamethasone administration caused an enhancement of neutrophil random migration and a suppression of neutrophil oxidative metabolism, iodination, and ADCC. None of the dosage levels of ascorbic acid had an effect on the alterations in the WBC count induced by dexamethasone. The ascorbic acid did tend to reverse the effects of dexamethasone on neutrophil random migration, oxidative metabolism, and ADCC in a dose-dependent manner, with the lowest dose having no discernible effect. Ascorbic acid administration also tended to enhance Staphylococcus aureus ingestion by bovine neutrophils. These results indicate that ascorbic acid should be further investigated for its potential to reduce the susceptibility of stressed or glucocorticoid-treated cattle to infective processes.     

Effect of levamisole on lymphocyte blastogenesis and neutrophil function in dexamethasone-treated cattle

Levamisole was evaluated at 6 dose levels for its ability to prevent the dexamethasone-induced suppression of in vitro lymphocyte blastogenesis or neutrophil function in cattle. Dexamethasone (0.4 mg/kg of body weight, IM) and levamisole hydrochloride (0.5, 1.0, 2.0, 4.0, or 8.0 mg/kg orally) were administered to groups of 4 cattle daily for 3 days. Another group of 4 cattle were given the 3-day dexamethasone treatment and 6.0 mg/kg of levamisole (the recommended anthelmintic dose) was given only once on the 1st day that dexamethasone was given. Results obtained from the dexamethasone-levamisole-treated cattle were compared with results obtained from cattle that were given only dexamethasone. Levamisole had no apparent consistent ability to enhance lymphocyte blastogenic responsiveness (to the mitogens phytohemagglutinin, concanavalin A, or pokeweed mitogen or in a 1-way mixed lymphocyte reaction) or to enhance neutrophil function (random migration, nitroblue tetrazolium reduction, iodination, or antibody-dependent cell-mediated cytotoxicity) in dexamethasone-treated cattle.     

Effects of dexamethasone, levamisole, and dexamethasone-levamisole combination on neutrophil function in female goats

Effects of dexamethasone, levamisole, or combined dexamethasone-levamisole administration on polymorphonuclear neutrophil (PMN) function in healthy, adult female goats were studied. Goats were assigned to treated (n = 6) and control (n = 6) groups. In experiment 1, treated goats were given levamisole (6 mg/kg of body weight, IM). In experiment 2, treated goats were given 0.1 mg of dexamethasone/kg, IV, for 3 consecutive days, 1 mg of dexamethasone/kg, IV, for 6 consecutive days, and 6 mg of levamisole/kg, IM, with a 4th injection of 1 mg of dexamethasone/kg. All injections were administered 12 hours before blood collection. The PMN were evaluated for random migration and chemotaxis under agarose, ingestion of Staphylococcus aureus, cytochrome C reduction, iodination, and antibody-dependent cell-mediated cytotoxicity. Levamisole alone did not alter the function of caprine PMN. Both doses of dexamethasone caused increased random migration and decreased cytochrome C reduction and iodination. Dexamethasone resulted in no changes in chemotaxis, S aureus ingestion, and antibody-dependent cell-mediated cytotoxicity. Random migration and cytochrome C reduction returned toward base line in cells from dexamethasone and levamisole-treated goats. Although iodination activity in cells from dexamethasone-treated goats remained significantly (P less than 0.05) lower than those of controls after levamisole administration, a rebound toward base-line activity occurred.     

Suppression of neutrophil and lymphocyte function induced by a vaccinal strain of bovine viral diarrhea virus with and without the administration of ACTH

Effects of a modified live vaccine (MLV) strain of bovine viral diarrhea virus (BVD) on lymphocyte and neutrophil function were determined in cattle with and without increased plasma cortisol (hydrocortisone) concentrations. Cattle were given MLV-BVD vaccine IM and intranasally. Cattle given ACTH received 200 IU every 12 hours for 10 doses. The MLV-BVD virus when administered alone caused no apparent clinical signs or body temperature response. Of 4 MLV-BVD-treated calves that were also given ACTH, 2 developed increased body temperature and respiratory distress. The MLV-BVD virus caused a decrease in circulating lymphocytes and neutrophils, whereas administration of ACTH and MLV-BVD induced a neutrophilia and lymphopenia. The MLV-BVD virus and ACTH when administered separately or in combination caused a depression of lymphocyte blastogenesis in response to selected mitogens. Neutrophils were separated from the peripheral blood and their function was evaluated, using the following procedures: (i) random migration under agarose, (ii) ingestion of 125I-labeled Staphylococcus aureus, (iii) quantitative nitroblue tetrazolium reduction, (iv) iodination, and (v) antibody-dependent cell-mediated cytotoxicity (ADCC). The MLV-BVD virus produced a significant (P less than 0.05) suppression of neutrophil iodination and ADCC. Neutrophils from cattle given MLV-BVD virus and ACTH had enhanced random migration, enhanced S aureus ingestion, suppressed iodination, and suppressed ADCC activity.     

Alteration of neutrophil function associated with coccidiosis in cattle: influence of decoquinate and dexamethasone

Twenty Holstein steers subclinically infected with coccidia were allotted to 2 groups of 10 steers each. One group received a diet containing 0.5 mg of decoquinate/kg of body weight. After 25 days on the diet, there was no difference between the groups in lymphocyte blastogenic responsiveness to mitogens; however, there were differences in neutrophil function. Lymphocytes from steers of the decoquinate-fed group had decreased random migration under agarose, enhanced cytochrome C reduction, and enhanced iodination activity. Other measures of neutrophil function evaluated (chemotactic index, Staphylococcus aureus ingestion, and antibody-dependent and -independent cell-mediated cytotoxicity) were not affected. After 30 days of decoquinate feeding, half of the cattle in each group received 5 daily IM injections of dexamethasone (0.04 mg/kg of body weight). The dexamethasone-treated steers from the group that did not have decoquinate in the diet developed clinical coccidiosis, whereas the decoquinate-treated steers remained clinically normal. Lymphocyte and neutrophil function were again evaluated for a 3-day period beginning 4 days after dexamethasone treatment was halted. Neutrophils from the steers that developed clinical coccidiosis after dexamethasone administration had significantly (P less than 0.05) inhibited random migration under agarose, cytochrome C reduction, and iodination activity, but significantly (P less than 0.01) enhanced S aureus ingestion. The feeding of decoquinate prevented the inhibition of neutrophil cytochrome C reduction and lessened the inhibition of neutrophil iodination in the dexamethasone-treated group. Dexamethasone treatment was associated with an inhibition of lymphocyte blastogenic responsiveness to phytohemagglutinin in principals as well as controls.     

The effects of glucocorticosteroids on the chemiluminescence response of bovine phagocytic cells

The effects of corticosteroids on the chemiluminescence response of bovine phagocytic cells were determined both in vitro and in vivo. The in vitro addition of hydrocortisone or dexamethasone had no significant effect on the chemiluminescence response of leukocytes in a whole blood or purified polymorphonuclear leukocyte (PMN) population. Cattle that received a single 20 mg dose of dexamethasone or three 20 mg doses of dexamethasone (given 24 hours apart) demonstrated the expected effects on the bovine leukogram (leukocytosis, neutrophilia, lymphopenia, eosinopenia, and monocytosis) and also demonstrated the expected suppressive effect on lymphocyte response to phytohemagglutinin (PHA). However, neither a single nor multiple dexamethasone treatment(s) had an effect on the chemiluminescence response of phagocytes in whole blood, but significantly enhanced the chemiluminescence response of the purified PMN leukocyte population. There was no significant difference between the two dexamethasone treatment groups in either the degree or duration of the effects observed in the chemiluminescence or lymphocyte response assays.     

Influence of recombinant human interleukin-2 administration on lymphocyte and neutrophil function in clinically normal and dexamethasone-treated cattle

Recombinant human interleukin-2 (rhIL-2) was evaluated for its influence on total and differential WBC counts, lymphocyte blastogenic responsiveness to mitogens, and several measurements of neutrophil function in clinically normal and in dexamethasone-treated cattle. A single dose of rhIL-2 (2.5 X 10(7) U) given SC had no influence on the total or differential WBC count; however, it did cause an inhibition of neutrophil random migration. The other measurements of neutrophil function (Staphylococcus aureus ingestion, cytochrome C reduction, iodination, and antibody-dependent and antibody-independent cell-mediated cytotoxicity) evaluated were not significantly altered. The rhIL-2 treatment was associated with a significant (P less than 0.01) decrease in uptake of [3H]thymidine in unstimulated lymphocytes and a tendency toward enhanced blastogenesis of lymphocytes stimulated with phytohemagglutinin. This enhancement was significant (P less than 0.05) only when the results were expressed as a stimulation index. Lymphocyte responsiveness to concanavalin A and pokeweed mitogen was not significantly influenced by rhIL-2 administration. Dexamethasone (0.04 mg/kg) administered every 24 hours for 3 consecutive days altered the WBC count and several measurements of lymphocyte and neutrophil function. The administration of a single dose of rhIL-2 (2.5 X 10(7) U) 8 hours after the first dose of dexamethasone did not alter the influence of dexamethasone on any of the measurements. These results indicated that rhIL-2 has some biologic activity in cattle, but when used as administered here, did not overcome the influence of dexamethasone on the in vitro measurements of lymphocyte and neutrophil function that were evaluated.     

Effects of dexamethasone on emesis in cats sedated with xylazine hydrochloride

OBJECTIVE: To determine antiemetic efficacy of prophylactic administration of dexamethasone and its influence on sedation in cats sedated with xylazine hydrochloride. ANIMALS: 6 healthy adult cats (3 males and 3 females). PROCEDURE: The prophylactic antiemetic effect of 4 doses of dexamethasone (1, 2, 4, and 8 mg/kg of body weight, IM) or saline (0.9% NaCl) solution (0.066 ml/kg, IM) administered 1 hour before administration of xylazine (0.66 mg/kg, IM) was evaluated. Cats initially were given saline treatment (day 0) and were given sequentially increasing doses of xylazine on days 7, 14, 21, and 28. After xylazine injection, all cats were observed for 30 minutes to allow assessment of frequency of emesis and time until onset of the first emetic episode.The influence of dexamethasone on xylazine-induced sedation in these cats also was evaluated. RESULTS: Prior treatment with 4 or 8 mg/kg of dexamethasone significantly reduced the frequency of emetic episodes and also significantly prolonged the time until onset of the first emetic episode after xylazine injection. Time until onset of the first emetic episode also was significantly prolonged for dexamethasone at a dose of 2 mg/kg. Time until onset of sedation after administration of xylazine was not altered by administration of dexamethasone. CONCLUSIONS AND CLINICAL RELEVANCE: Dexamethasone (4 or 8 mg/kg, IM) significantly decreased the frequency of emetic episodes induced by xylazine without compromising sedative effects in cats. Dexamethasone may be used prophylactically as an antiemetic in cats treated with xylazine.     

Effects of ACTH administration on bovine polymorphonuclear leukocyte function and lymphocyte blastogenesis

Yearling steers were treated with ACTH to determine the effect of increased plasma cortisol concentration on bovine lymphocyte and polymorphonuclear leukocyte (PMN) function. The administration of ACTH caused a significant (P less than 0.01) increase in serum cortisol concentration and depression of lymphocyte blastogenesis in response to phytohemagglutinin and concanavalin A. The response to pokeweed mitogen was also depressed, but not significantly. Random migration by PMN was significantly enhanced by ACTH treatment, but there was no effect on ingestion of Staphylococcus aureus, nitroblue tetrazolium reduction, or antibody-dependent cell-mediated cytotoxicity by PMN. The iodination reaction, which evaluates the activity of the myeloperoxidase-hydrogen peroxide-halide antibacterial system of the PMN, was significantly impaired after ACTH treatment. These data indicate that specific parameters of lymphocyte and neutrophil function were impaired directly or indirectly by elevated in vivo concentrations of plasma cortisol.     

Association of increased estradiol and progesterone blood values with altered bovine polymorphonuclear leukocyte function

Polymorphonuclear leukocyte (PMN) function and serum concentrations of estradiol, progesterone, and cortisol (hydrocortisone) were monitored concurrently in clinically normal cows during the estrous cycle. Five parameters were used to evaluate PMN function: (i) random migration under agarose, (ii) ingestion of 125I-labeled Staphylococcus aureus, (iii) nitroblue tetrazolium (NBT) reduction, (iv) iodination, and (v) antibody-dependent cell-mediated cytotoxicity. Increased serum estradiol concentrations were associated with enhanced random migration, but had no apparent effect on NBT reduction, iodination, or ingestion of S aureus by bovine PMN. Increased serum estradiol was also associated with increased serum cortisol. Increased serum progesterone values were associated with a depression of NBT reduction and iodination by PMN, but with enhanced random migration and antibody-dependent cell-mediated cytotoxicity. These results indicate that physiologic changes in steroid hormone values during the normal estrous cycle of the cow are associated with alterations in PMN function.     

Response of Pasteurella haemolytica to erythromycin and dexamethasone in calves with established infection.

A subcutaneous soft tissue infection model in calves was used to study the in vivo response of Pasteurella haemolytica to erythromycin and dexamethasone. Two tissue chambers were implanted SC in each of 12 calves. At 45 days after implantation, all tissue chambers were inoculated with an erythromycin-sensitive strain of P haemolytica. Starting 24 hours after inoculation, calves were allotted to 4 groups of equal size and a 2 x 2-factorial arrangement of treatments was applied: 3 calves were given erythromycin (30 mg/kg of body weight, IM, for 5 days), 3 calves were given dexamethasone (0.05 mg/kg, IM, for 2 days), 3 calves were given erythromycin and dexamethasone, and the remaining calves served as nontreated controls. Chamber fluids were tested daily, and the response to treatment was measured. Neither erythromycin nor dexamethasone affected viability or growth of bacteria within tissue chambers. Dexamethasone had no effect on the influx of neutrophils into infected chambers. Despite repeated administration of a high dose of erythromycin and attainment of adequate concentration in serum, erythromycin concentration in chamber fluids did not exceed the minimal inhibitory concentration established in vitro. These results indicate that the clinical efficacy of erythromycin against P haemolytica sequestered in consolidated pneumonic lesions may not be well correlated with predictions based on serum pharmacokinetic and in vitro susceptibility data.     

The Effect of Dexamethasone on Some Immunological Parameters in Cattle

Immunosuppression as a consequence of acute and chronic stress can increase the susceptibility of cattle to a range of infectious diseases. In order to develop a panel of immune function assays for investigating the effects of potential stressors on immune competence in cattle, the effect of treatment with short- and long-acting preparations of the synthetic glucocorticoid dexamethasone was examined. Short-acting dexamethasone (dexamethasone sodium phosphate 0.08 mg/kg) followed 37 h later by long-acting dexamethasone (dexamethasone-21 isonicotinate 0.25 mg/kg) was injected intramuscularly and blood was collected to assess immune functions at intervals over the subsequent 11 days from 6 treated and 6 control Hereford steers. Dexamethasone induced leukocytosis (neutrophilia, eosinopenia, lymphopenia, monocytosis), an increased neutrophil:lymphocyte ratio, an elevated percentage of CD4⁺ lymphocytes, a decreased total CD8⁺ lymphocyte count, decreased total and percentage WC1⁺ lymphocytes, an elevated percentage of IL-2 receptor alpha (IL-2R)⁺ lymphocytes, and an elevated percentage of B lymphocytes. In vitro chemotaxis of peripheral blood neutrophils to human C5a and ovine IL-8 was increased by dexamethasone treatment. Lymphocyte proliferation in the presence of phytohaemagglutinin, and serum concentrations of IgM, but not IgA or IgG1, were suppressed by dexamethasone treatment, whereas mitogen-induced production of interferon- (IFN-), neutrophil expression of CD18, neutrophil myeloperoxidase activity and natural killer (NK) cell activity were not influenced by dexamethasone treatment. The results indicate the potential for haematology and immune function assays to reflect elevated activity of the hypothalamic–pituitary–adrenocortical axis in cattle. Immunological parameters may thus provide a useful adjunct to cortisol and behavioural observations for assessing the impact of stress on the welfare of cattle.     

Pharmacokinetics of dexamethasone after intravenous and intramuscular administration in broiler chickens

The aim of this study was to determine the pharmacokinetics of dexamethasone in broiler chickens. Dexamethasone sodium phosphate (0.3 mg/kg bodyweight) was injected IV or IM and blood samples were collected at 0, 0.25, 0.5, 0.75, 1, 2, 4, 6, 8, 10, 12 and 24 h after administration. Dexamethasone in the plasma samples was measured using a liquid chromatography–tandem mass spectrometry method and the pharmacokinetics analysed according to a one-compartmental model.The maximum plasma concentration after IM administration occurred at 0.37 h. The elimination half-life for dexamethasone was 0.46 h and 0.70 h following IV and IM administration, respectively, which was shorter than other species, while the clearance (1.26 L/h kg) was higher than has been reported for other species (<0.5 L/h kg). The volume of distribution (～1 L/kg) was similar to values reported for other species and the bioavailability of dexamethasone after IM administration was 100%. The results from this study will be useful in investigating whether inflammatory disease may affect the pharmacokinetic parameters of dexamethasone in chickens.     

In vivo effects of a thymosin alpha 1-containing colostral whey product on neutrophils and lymphocytes from lactating cows without and with experimentally induced Staphylococcus aureus mastitis

Two separate experiments evaluated ID-1 (a commercial bovine whey product containing 5200 pg of thymosin alpha 1/ml) as an immunotherapeutic agent in lactating cows. In the first experiment, cows without mastitis were evaluated for blood leukogram, milk production, total and differential milk cell counts, lymphocyte (Lc) blastogenesis, and neutrophil (PMN) functions (random and directed migration under agarose, chemiluminescence, ingestion of bacteria, iodination, cytochrome C reduction, antibody-independent neutrophil-mediated cytotoxicity, and antibody-dependent cell-mediated cytotoxicity) before and after ID-1 therapy. ID-1 treatment resulted in a significant treatment group by time period interaction for the relative proportion of mononuclear cells (MNC) in milk (P less than 0.009) and for PMN random migration (P less than 0.01). Based on these interactions, ID-1 treatment appeared to slightly increase the proportion of small MNC in milk and to increase random migration from pretreatment levels by 73% more than increases observed in controls. No significant effect of ID-1 treatment on milk production, total milk somatic cell counts, Lc blastogenesis, or other PMN functions was observed. In cows with experimental Staphylococcus aureus intramammary infections, ID-1 treatment resulted in a significant decline in blood leukocyte count (P less than 0.001) and blood PMN count (P less than 0.02), and maintained PMN random migration (P less than 0.01) while controls declined and abrogated a depression in the ability of Lc to respond to mitogens (P less than 0.05) that developed in controls as a result of S. aureus mastitis. Injection of ID-1 into cows had no adverse effect on their overall health or level of milk production, but did cause subtle and potentially favorable changes in several in vitro immune parameters. In spite of these subtle changes which might indicate increased resistance to mastitis, cows actually developed a more severe S. aureus intramammary infection based on a 9% increase in log 10 bacterial shedding in milk.     

Effect of dexamethasone on babesiasis in hamsters

Three subcutaneous injections of 0.20 mg of dexamethasone/kg of body weight caused a substantial increase in Babesia microti-parasitized RBC of hamsters, indicating that this was a useful method for revealing the presence of latent infections. A relative neutrophilia, lymphocytopenia, and eosinopenia were also seen in the long-term B microti-infected carrier hamsters after 0.20 mg or 0.02 mg of dexamethasone/kg. Noninfected hamsters treated with dexamethasone had a neutrophilic leukocytosis and a transient lymphocytopenia. Spleen to body weight ratios of noninfected hamsters decreased significantly (P less than 0.02) after 4 injections with either dosage level. These ratios did not significantly (P greater than 0.05) decrease in dexamethasone-treated infected hamsters.     

Efficacy of oral and intravenous dexamethasone in horses with recurrent airway obstruction

REASONS FOR PERFORMING STUDY: Although the efficacy of dexamethasone for the treatment of recurrent airway obstruction (RAO) has been documented, the speed of onset of effect and duration of action are unknown, as is the efficacy of orally administered dexamethasone with or without fasting. OBJECTIVES: To document the time of onset of effect and duration of action of a dexamethasone solution i.v. or orally with and without fasting. METHODS: Protocol 1 used 8 RAO-affected horses with airway obstruction in a crossover design experiment that compared the effect of i.v. saline and dexamethasone (0.1 mg/kg bwt) on pulmonary function over 4 h. Protocol 2 used 6 similar horses to compare, in a crossover design, the effects of dexamethasone i.v. (0.1 mg/kg bwt), dexamethasone per os (0.164 mg/kg bwt) with and without prior fasting, and dexamethasone per os (0.082 mg/kg) with fasting. RESULTS: Dexamethasone i.v. caused significant improvement in lung function within 2 h with a peak effect at 4-6 h. Dexamethasone per os was effective within 6 h with peak effect at 24 h at a dose of 0.164 mg/kg bwt prior to feeding. The duration of effect was, for all dexamethasone treatments, statistically significant for 30 h when compared to saline and tended to have a longer duration of effect when used orally. Dexamethasone per os at a dose of 0.164 mg/kg bwt to fed horses had mean effects comparable to dexamethasone at a dose of 0.082 mg/kg bwt per os given to fasted horses, indicating that feeding decreases bioavailability. CONCLUSIONS: Dexamethasone administered i.v. has a rapid onset of action in RAO-affected horses. Oral administration of a bioequivalent dose of the same solution to fasted horses is as effective as i.v. administration and tends to have longer duration of action. Fasting horses before oral administration of dexamethasone improves the efficacy of treatment. POTENTIAL RELEVANCE: Oral administration to fasted horses of a dexamethasone solution intended for i.v. use provides an effective treatment for RAO-affected animals.     

Dexamethasone-induced immunosuppression: a rabbit model

Rabbits are often used as animal models for experimental purposes; in many cases steroid-induced immunosuppression is necessary. The aim of this study was to characterise a model of immunosuppression in rabbits, based on changes in the lymphocyte subset distribution, changes in proliferative capacity of lymphocytes and activity of neutrophils 1, 3 and 7 days after the administration of 2mg/kg dexamethasone phosphate (DXP) three times at 6-h intervals. In peripheral blood, neutrophilia and lymphopenia together with eosinopenia, monocytopenia and basopenia in the absence of leukocytosis was detected. One day after DXP administration the absolute numbers of all lymphocyte subsets decreased in the blood, whereas in bone marrow, absolute numbers of all lymphocyte subsets increased significantly, except CD79alpha(+) cells that increased only in relative numbers. The effect of DXP on lymphocytes from the spleen, mesenteric and popliteal lymph nodes was less pronounced. In the thymus, DXP led to a marked reduction of the relative and absolute numbers of CD4(+)CD8(+) thymocytes. The proliferative capacity of lymphocytes after concanavalin A stimulation was lower in the peripheral blood and spleen only on day 1, no changes were detected in lymph nodes or in bone marrow. A marked increase in proliferative capacity was detected in the thymus. Spontaneous production of reactive oxygen metabolites by neutrophils was reduced on days 1 and 3 after DXP administration. The present results demonstrate clearly that this DXP application protocol is useful for the experimental induction of relatively short-lasting immunosuppression in rabbits.     

In vitro depression of bovine lymphocyte function by treatment of cultured bovine lymphocytes with physiologic concentrations of hydrocortisone

The effect of hydrocortisone (hydrocortisone sodium succinate) on bovine lymphocyte blastogenesis in response to Staphylococcus aureus antigens and phytohemagglutinin was measured in vitro. Lymphocytes isolated from the blood of cows were treated for 6 to 8 days with physiologic hydrocortisone concentrations known to be inducible by environmental stress (10 ng/ml), acute clinical mastitis (25 ng/ml), or adrenocorticotropin treatment (45 ng/ml). All 3 concentrations of hydrocortisone caused a depression (P less than 0.01) in lymphocyte blastogenesis in response to phytohemagglutinin and S aureus antigen extract. Hydrocortisone concentrations as low as 10 pg/ml caused a depression in the lymphocyte blastogenic response to phytohemagglutinin. Marked variation existed among cows in the normal response of their nontreated lymphocytes and in the degree of depression of lymphocyte function after the in vitro treatment with hydrocortisone. Macrophage depletion experiments showed that the suppressive effect of hydrocortisone was not mediated by induction of suppressor macrophages. The data suggest that T-cell function was impaired directly by hydrocortisone treatment.     

Evaluation of antibiotics for treatment of cattle infected with Leptospira borgpetersenii serovar hardjo

OBJECTIVE: To evaluate antibiotics for treatment of cattle with leptospirosis caused by Leptospira borgpetersenii serovar hardjo. DESIGN: Randomized controlled trial. ANIMALS: 42 healthy mixed-breed cattle. PROCEDURE: Cattle were inoculated via conjunctival instillation with L. borgpetersenii serovar hardjo. After infection and urinary shedding of L. borgpetersenii were confirmed, cattle were treated with various antibiotics. To determine effectiveness of antibiotic treatment, urinary shedding of L. borgpetersenii was monitored for 4 to 6 weeks after administration of antibiotics, using darkfield microscopic examination, microbial culture, immunofluorescence testing, and a polymerase chain reaction assay. RESULTS: All inoculated cattle developed leptospirosis and shed leptospires in their urine. The following antibiotic treatments resulted in elimination of urinary shedding of leptospires: a single injection of oxytetracycline (20 mg/kg 19 mg/lb] of body weight, IM), tilmicosin (10 mg/kg [4.5 mg/lb], SC), or a combination product that contained dihydrostreptomycin-penicillin G (25 mg/kg [11.4 mg/lb], IM) or multiple injections of ceftiofur sodium (2.2 or 5 mg/kg [1 or 2.3 mg/lb], IM, once daily for 5 days, or 20 mg/kg, IM, once daily for 3 days). CONCLUSIONS AND CLINICAL RELEVANCE: Successful resolution of leptospirosis in cattle by administration of dihydrostreptomycin-penicillin G confirms results obtained by other investigators. Three other antibiotics (oxytetracycline, tilmicosin, and ceftiofur) also were effective for resolving leptospirosis and may be useful substitutes for dihydrostreptomycin, an antibiotic that is no longer available for use in food-producing animals in the United States. Cost, safety, and withdrawal times of these various treatment options need to be considered.     

Effects of multiple intramuscular injections and doses of dexamethasone on plasma cortisol concentrations and adrenal responses to ACTH in horses

Adrenocortical function was assessed in horses given multiple IM doses of dexamethasone to determine the duration of adrenocortical suppression and insufficiency caused by 2 commonly used dosages of dexamethasone (0.044 and 0.088 mg/kg of body weight). Dexamethasone was administered at 5-day intervals for a total of 6 injections. Daily blood samples were collected. The plasma was frozen and later assayed for cortisol. An ACTH response test was determined 2 days before the first injection of dexamethasone and again 8 days after the last dexamethasone injection. Maximum suppression of plasma cortisol was observed in horses given both dosages of dexamethasone (0.044 and 0.088 mg/kg). Plasma cortisol concentrations returned to base-line values in all horses by 4 days after dexamethasone injection. Normal ACTH responses observed after 6 dexamethasone injections given at 5-day intervals indicated that measurable adrenal atrophy did not develop under the conditions of this study.