Antimicrobial susceptibilities of Mycoplasma isolated from bovine mastitis in Japan

Mycoplasma spp. are highly contagious pathogens and intramammary Mycoplasma infection is a serious issue for the dairy industry. As there is no effective vaccine for Mycoplasma infection, control depends on good husbandry and chemo‐antibiotic therapy. In this study, antimicrobial susceptibility of Mycoplasma strains recently isolated from cases of bovine mastitis in Japan was evaluated by minimum inhibitory concentration (MIC). All Mycoplasma bovis strains were sensitive to pirlimycin, danofloxacin and enrofloxacin, but not kanamycin, oxytetracycline, tilmicosin or tylosin. M. californicum and M. bovigenitalium strains were sensitive to pirlimycin, danofloxacin, enrofloxacin, oxytetracycline, tilmicosin and tylosin, but not to kanamycin. This is the first report to describe the MIC of major antimicrobial agents for Mycoplasma species isolated from bovine mastitis in Japan.     

Lincomycin and spectinomycin in the treatment of breeding rams with semen contaminated with ureaplasmas

Ureaplasma species were isolated from semen samples collected sequentially from one Awassi and three Assaf breeding rams. Each ram was injected subcutaneously with an aqueous solution of lincomycin and spectinomycin for five consecutive days at a dose equivalent to 4·5 mg kg⁻¹ lincomycin and 9·0 mg kg⁻¹ spectinomycin daily. Serum and semen samples were collected at intervals during the treatment and assayed for lincomycin. No Ureaplasma species were isolated from semen samples collected during the course of the treatment and at intervals for 17 days after the last treatment. The concentration of lincomycin in semen ranged from 0·51 μg ml⁻¹ four hours after treatment to 0·08 μg ml⁻¹ 24 hours after treatment, and these levels were three to nine times higher than the corresponding serum concentrations.     

Effect of stage of gestation and foetal number on plasma concentrations of a pregnancy serum protein (PSP-60) in cattle

This study characterised the peripheral plasma concentration of PSP-60 throughout gestation, and examined the effect of stage of gestation and foetal number on this protein in Holstein cows after non-surgical embryo transfer. Cows (n=12) were divided into two groups; Group 1 contained single embryo recipient cows (n=5), Group 2 contained twin-embryo recipient cows (n=7). Blood was collected approximately every third day from day 0 (first day of standing oestrus), then daily for the last 10 days of gestation and until one day post-partum. Two of the twin-embryo recipient cows had abnormal pregnancies, consequently data from them was considered separately. In both groups PSP-60 increased progressively from about day 20 post-oestrus to 20 days pre-partum (from 0·9 ± 0·2 to 49·7 ± 8·7 ng ml⁻¹, and from 1·3 ± 0·6 to 115 ± 34·9 ng ml⁻¹ (mean ± SEM), in singleton and twin-bearing groups, respectively). The mean concentrations between 20 and 10 days pre-partum increased dramatically by about six-fold (P<0·001) in singleton-bearing cows (from 49·7 ± 8·7 ng ml⁻¹ to 2838 ± 73·7 ng ml⁻¹) to over two-fold in twin-bearing cows (from 115 ± 34·9 ng ml⁻¹ to 284 ± 98·2 ng ml^-1). The mean concentrations of the two groups were indistinguishable between 10 days pre-parturn and parturition. Cows giving birth prematurely to stillborn calves or to a schistosomus reflexus calf exhibited abnormal PSP-60 profiles. Our findings indicate that peripheral plasma PSP-60 concentrations are correlated to the stage of gestation and foetal number, and assist in predicting foeto-placental viability.     

Effects of inhibition of nitric oxide synthase on systemic arterial pressure and renal vascular resistance in cats

These studies were undertaken to examine the systemic and renal effects of the pharmacological inhibition of endothelium-derived nitric oxide (EDNO) in cats. In six healthy cats, the intravenous infusion of nitro-L-arginine at a dose of 100 μg kg⁻¹ bodyweight min⁻¹ resulted in a marked increase (P<0·001) in mean arterial pressure from the control value of 116·7 ± 4·6 mmHg to 154·2 ± 6·8 mmHg and an increase (P<0·05) in renal vascular resistance from the control value of 3·69 ± 0·33 mmHg min ml⁻¹ to 6·83 ± 1·15 mmHg min ml⁻¹. The increase in renal vascular resistance was generalised, with comparable increments in preglomerular and postglomerular vascular resistance. Mean values for glomerular capillary pressure (61·1 ± 61·9 vs 1·9 ± 1·6 mmHg), calculated from the sum of arterial colloid osmotic pressure plus proximal tubule stop-flow pressure, did not change in response to the infusion of nitro-L-arginine. However, there was a marked reduction in renal blood flow (29·4 ± 3·1 to 16·9 ± 2·3 ml min⁻¹, P<0·01) and glomerular filtration rate (5·22 ± 0·57 to 3·52 ± 0·45 ml min⁻¹, P<0·01). These results provide evidence that EDNO plays an important role in the basal regulation of systemic arterial blood pressure and renal haemodynamics in cats.     

Simple continuous and simultaneous determination of tetracycline residues

A new continuous separation method was developed for the determination of five different tetracyclines (oxytetracycline, tetracycline, chlortetracycline, methacycline and doxycycline). A bioassay using minimum medium (mm) seeded with Bacillus subtilisatcc 6633 was carried out for the detection, with simple extraction from the agar block of the clear inhibition zone on the MM produced by the mixed tetracyclines. The extract was subjected to continuous identification by high performance liquid chromatography using a μ-Bondapack C₁₈ column. The tetracyclines were separated at ambient temperature using a mobile phase of 0·01 M oxalic acid: acetonitrile: N,N-dimethylformamide (74:18:8, v/v/v) at a flow rate of 1·0 ml min⁻¹. A variable-wavelength detector set at 355 nm and recorder set at 4 mm min⁻¹ were used for the detection. The entire mixture was resolved as five peaks with retention times ranging from 2·75 to 9·65 minutes. This continuous, simple and rapid method of detection, extraction and identification may be useful for routine laboratory testing of residual antimicrobial agents in food.     

Sensitivity of Certain Porcine and Bovine Mycoplasmas to Antimicrobial Agents in a Liquid Medium Test Compared to a Disc Assay

The sensitivity of some porcine and bovine mycoplasmas to potent antimicrobial agents was examined. Minimal inhibitory concentration (MIC) values were estimated for M. hyosynoviae, M. hyopneumoniae, M. dispar and M. bovis against enrofloxacin, lincomycin, tetracycline, tiamulin and tylosin, in a liquid medium test and in a disc assay. All 6 examined strains of each species and the respective type strains were significantly inhibited. The greatest sensitivity was noted for tiamulin against strains of M. hyosynoviae with a final MIC₅₀ broth value of 0.025 µg ml⁻¹ and disc value of 0.03 µg per disc. Enrofloxacin was found very potent against M. hyopneumoniae with a final MIC₅₀ of 0.025 µg ml⁻¹ and 0.1 µg per disc, and for M. dispar with 0.05 µg ml⁻¹ and 0.03 µg per disc.Most disc assay estimates in ug per disc were similar to or moderately greater than corresponding final broth figures in µg ml⁻¹. It may be possible to convert observed disc assay values into representative final broth MIC values for use in the clinic.     

Pathology and residues in veal calves treated experimentally with clenbuterol

Six veal calves were medicated with clenbuterol at 20 μg kg bodyweight⁻¹ day⁻¹ for 42 days before they were slaughtered, to evaluate the lesions and residues in target organs. Compared with six unmedicated calves the most noticeable changes were tracheal dilatation, decreased uterine weight, slight mucous hypersecretion in the uterus and vagina and depletion of liver glycogen. The highest concentrations of clenbuterol (62 to 128 ng/g⁻¹) were recorded in the choroid/retina, and the aqueous humour had the lowest concentration (0·5 to 2·4 ng ml⁻¹). The residue concentrations were higher than the maximum residue level set for clenbuterol (0·5 ng g⁻¹)     

Purification and quantitative measurement of bovine serum amyloid-A

Bovine serum amyloid-A (b-SAA) was purified from a pool of acute phase serum using hydrophobic interaction chromatography and gel filtration. Serum was applied at a low salt concentration to a phenyl-sepharose column and SAA was eluted with a gradient of 0 to 6 M guanidine-HCI. Fractions containing SAA were pooled, concentrated and further purified by gel filtration on Superose-12. The concentration of SAA in bovine serum was quantified by an indirect ELISA using rabbit anti-human SAA and horseradish peroxidase conjugated donkey anti-rabbit IgG. Dilutions of an acute phase bovine serum sample were used as working standards. The SAA concentration of this standard was determined by comparison with purified b-SAA on SDS-polyacrylamide gel electrophoresis followed by densitometry at 590 nm. The assay detection limit was 3 μg ml⁻¹; the intra-assay coefficient of variation was 4 per cent and interassay coefficients of variation were 5·5 per cent and 7·2 per cent at 66 and 178 μg ml⁻¹ SAA, respectively. In calves experimentally infected with Pasteurella haemolytica type A1 the ELISA was able to detect a 10-fold increase of SAA within 24 hours of inoculation.     

In vitro susceptibility of avian Escherichia coli and Pasteurella multocida to danofloxacin and five other antimicrobials.

The in vitro susceptibility of Escherichia coli and Pasteurella multocida isolated from poultry was determined to danofloxacin, a novel fluoroquinolone, and five other commonly used antimicrobials. A total of 1737 E. coli field isolates and 107 P. multocida isolates were tested by veterinary diagnostic laboratories in Europe, Japan, South Africa, and North America during the period 1989-91. The antimicrobial susceptibility of these isolates was determined using the Sensititre broth microdilution technique. The minimum inhibitory concentrations (MIC) of danofloxacin, furaltadone, lincomycin, oxytetracycline, spectinomycin, and trimethoprim:sulfamethoxazole that prevented growth of 90% of the bacteria were 0.25 > 64, > 64, > 64, > 128, and > 16 micrograms/ml, respectively, against E. coli isolates and 0.25, 64, 64, 16, 128, and 8 micrograms/ml, respectively, against P. multocida isolates. Danofloxacin demonstrated considerable in vitro potency against these important poultry pathogens, many of which showed extensive resistance to the other antimicrobials tested.     

Uterine activity after ovariectomy in the camel (Camelus dromedarius): effect of exogenous administration of oestrogen and progesterone

During oestrous cycles of the camel, spontaneous uterine contractions were correlated significantly with plasma oestradiol-17β concentration. Ovariectomy in the camel resulted in a decreased plasma concentration of oestradiol-17β (<15 pg ml⁻¹) and progesterone (<0·1 ng ml⁻¹) and caused complete cessation of uterine activity. Daily administration of oestradiol benzoate (5 mg, intramuscularly) increased the plasma concentration of oestradiol-17β (>45 pg ml⁻¹) and increased the frequency and amplitude of uterine activity. Coadministration of progesterone (100 mg, intramuscularly) increased the plasma concentration of progesterone (>4 ng ml⁻¹) and increased the frequency but not amplitude of uterine activity. It is suggested that uterine activity in the camel is correlated with the circulating levels of oestradiol-17β and progesterone.     

Disposition and urinary excretion of phenylbutazone in normal and febrile greyhounds

Five days after the induction of acute systemic inflammation in greyhounds by intramuscular and subcutaneous injections of Freund's adjuvant, the hepatic concentrations of cytochromes P-450 and b₅, the activities of the hepatic microsomal enzymes aniline p-hydroxylase and aminopyrine n-demethylase and the disposition and urinary excretion of phenylbutazone were determined. The mean plasma concentrations of phenylbutazone after intravenous administration were described by the bi-exponential equations: Cp = 144·2e^−34·6t + 171·5e^−0·104t for five normal greyhounds and Cp = 113·6e^−16·13t + 163·1e^−0·108t for five febrile greyhounds. The elimination half-lives, total body clearances and apparent volumes of distribution were 6·7 hours, 18·4 ml kg⁻¹ hour⁻¹ and 0·18 litre kg⁻¹, for the normal greyhounds, and 6·4 hours, 19·5 ml kg⁻¹ hour⁻¹ and 0·18 litre kg⁻¹, for the febrile greyhounds. There were no significant differences between the pharmacokinetic parameters describing the distribution and elimination of phenylbutazone, or between the quantities of phenylbutazone, oxyphenbutazone and hydroxyphenylbutazone excreted in the urine. In the febrile greyhounds, there were significant decreases in the hepatic microsomal concentrations of cytochromes P-450 and b₅ and in the activities of aniline p-hydroxylase and aminopyrine n-demethylase.     

Blood lactate disappearance after maximal exercise in trained and detrained horses

The influence of training on blood lactate concentrations during treadmill exercise and a 40-minute inactive recovery period was examined in seven trained and seven detrained thorough-bred horses. Lactate concentrations were measured in venous blood collected at the end of each exercise state, and at intervals for 40 minutes afterwards. Measurements were made of maximum oxygen uptake (V̇O_2max, ml kg⁻¹ min⁻¹), VLA4 (velocity at which blood lactate concentration was 4 mmol litre⁻¹); LA8 (lactate concentration [mmol litre⁻¹] during exercise at 8 m sec⁻¹), peak lactate (highest lactate concentration after exercise), LA40 (lactate concentration 40 minutes after exercise), the time of peak lactate concentration (minutes after exercise) and the rate of disappearance of blood lactate (Rt_d). The trained horses had a significantly lower LA8 (2·1 ± 0·1 vs 6·5 ± 1 mmol litre⁻¹, P<0·01), higher VLA4 (9·8 ± 0·2 vs 5·8 ± 0·6 m sec⁻¹, P<0·01) and higher V̇0_2max (156·3 ± 3·8 vs 107·1 ± 3·9 ml kg⁻¹ min⁻¹, P<0·001). The value of Rt_d and the time of peak lactate concentration were not significantly different.     

Comparison of carprofen and flunixin meglumine asadjunctive therapy in bovine respiratory disease

In an open, controlled, multi-centre clinical field trial, seven ‘naturally occurring’ outbreaks of acutefebrile (rectal temperature ≥ 39·5°C) respiratory disease in housed calves were treated with a single antimicrobial agent, and either the non-steroidal anti-inflammatory drug (NSAID) carprofen (n=95) or flunixin meghunine (n=92) on an alternate basis. Carprofen was administered as a single subcutaneous injection at a mean dosage of 1·4 mg kg⁻¹ (range 1·2 to 1·9 mg kg⁻¹) body weight on the first day and flunixin meglumine by intravenous injection at a mean dosage of 2·0 mg kg⁻¹ (range 1·2 to 2·6 mg kg⁻¹) body weight on the first 3 consecutive days. All calves were examined clinically immediately prior to initial treatment and on three occasions up to 1 week after the end of treatment. There were no statistically significant differences between NSAID groups in reduction of clinical parameters between examinations, or in overall efficacy. This trial demonstrated that a single dose of carprofen was equally effective as three daily closes of flunixin meglumine as adjunctive therapy to antimicrobial treatment in acute respiratory disease in calves.     

Rumen degradation characteristics of sweet potato foliage and performance by local and crossbred calves fed milk and foliage from three cultivars

The study investigated rumen dry matter (DM) degradability characteristics in a completely randomized design and the effects of milk, sweet potato foliage (SPF) from three cultivars (A = TIS-87/0087; B = TIS-8164; C = TIS-2532.OP.1.13), dried brewers' grains (DBG) and cottonseed meal (CSM) as supplements to Panicum maximum (Panicum) for pre-weaned calves in randomized complete block designs. Diet 1 = milk + SPF-A foliage + Panicum, Diet 2 = milk + SPF-B foliage + Panicum, Diet 3 = milk + SPF-C foliage + Panicum, and Diet 4 = milk + DBG & CSM + Panicum (as control). Dry matter (130 ± 0.4 to 864 ± 3.9 g kg^− 1), ash (54 ± 4.2 to 173 ± 2.8 g kg^− 1 DM), OM (827 ± 4.2 to 946 ± 5.7 g kg^− 1 DM), N (7.4 ± 0.6 to 38.6 ± 1.4 g kg^− 1 DM), and NDF (439 ± 1.4 to 774 ± 8.5 g kg^− 1 DM) contents were highly significant (P < 0.01). In Trial I, 16 pre-weaned calves were used over 70 d with milk intake (34.8 ± 4.4 ml kg W^− 0.75 d^− 1), Panicum DMI (22.3 ± 2.77 g kg W^− 0.75 d^− 1), total DMI (35.7 ± 2.83 g kg W^− 0.75 d^− 1), and LWG (198 ± 44.6 g d^− 1) not significantly different (P > 0.05). Supplement DMI varied (P < 0.05) from 11.6 g kg W^− 0.75 d^− 1 in Diet 3 to 16.6 g kg W^− 0.75 d^− 1 in Diet 4. In Trial II, 16 pre-weaned local and crossbred calves were involved over 77 d with initial age of calves, Panicum intake, metabolic DMI, and LWG similar (P > 0.05) among crosses. Birthweight varied (P < 0.05) from 17.3 kg for N'Dama × Jersey crosses to 21.2 kg for White Fulani × Brown Swiss crosses. Supplement and total DMI ranged (P < 0.05) from 172 to 483 g d^− 1 for N'Dama × Jersey crosses to 233 and 674 g d^− 1 for non-inseminate or purebred calves, respectively. The LWG in the White Fulani × Brown Swiss and the N'Dama × Jersey calves were respectively 30% and 24% better, though not significantly, than purebred calves. In Trial III, rumen DM degradability characteristics of feeds in three N'Dama steers showed no significant differences (P > 0.05) in slowly degradable fraction (b) and rate of degradation of b (c). Soluble fraction (a), 48-h degradation, potential degradability (PD) and effective degradability (ED) varied significantly (P < 0.05) and were lowest in Panicum, but similar for foliage among the three sweet potato cultivars. Panicum fodder showed improvements in degradation characteristics with supplementation.     

Effect of dietary chloride content on the elimination of bromide by dogs

The effect of dietary chloride content (0·2, 0·4 and 1·3 per cent chloride on a dry matter basis) on the disposition of a single oral dose of bromide (14 mg kg⁻¹ was evaluated in normal beagles. Increasing the dietary chloride content from 0·2 to 1·3 per cent resulted in a significant decrease in the mean apparent elimination half-life from 69 ± 22 days to 24 ± 7 days. The mean area under the concentration curve ( ) for dogs fed 1·3 per cent chloride was significantly smaller than the for dogs fed 0·2 per cent chloride. Dietary chloride had no effect on the maximum serum concentrations (C_max) or on the time (T_max) to reach the maximum concentrations. The steady-state serum bromide concentrations predicted from the single dose data for daily doses of 14 mg kg⁻¹ of bromide were significantly lower in dogs fed 1·3 per cent chloride (310 ± 150 mg litre⁻¹) than in dogs fed 0·2 per cent chloride (1950 ± 1140 mg litre⁻¹). The predicted mean daily doses of bromide necessary to maintain serum levels within the therapeutic range for dogs fed 1·3 per cent chloride (43 ± 13 mg kg⁻¹) were almost twice as high as the dose estimated for dogs fed 0·4 per cent chloride (22 ± 3 mg kg⁻¹) and nearly three times as high as the dose estimated for dogs fed 0·2 per cent chloride (15 ± 4 mg kg^−l). These differences were statistically significant (P=0·002).     

Serum troponin T concentrations in two strains of commercial broiler chickens aged one to 56 days

Troponin T is a specific and sensitive serological indicator of acute myocardial infarction in human patients. The concentration of serum troponin T was measured by an technique in two strains of healthy commercial broiler chickens (Cobb 500 and Ross I) aged between one and 56 days. The concentrations of cardiac-derived troponin T in day-old Cobb and Ross chicks were 5·74 and 8·35 ng ml⁻¹, respectively, and much higher than in 14-day-old chicks. Between 21 and 56 days, the values were consistently lower than the mean troponin T concentration of 0·20 ng ml⁻¹ reported previously in a group of healthy 30-day-old broilers. All the other heart measurements, including the arterial pressure index, were within normal limits. The high troponin T concentrations after hatching are probably due to an embryonic isoform that rapidly becomes replaced by an adult isoform by three weeks of age. The data suggest that in healthy birds, there is an inverse relationship between troponin T concentrations and age.     

Epidermal and hepatic glucocorticoid receptors in cats and dogs

Low capacity, high affinity [³H] dexamethasone binding receptors were identified in cytosolic preparations of liver (mean number 45±10·1 fmol mg⁻¹ protein, apparent dissociation constant 0·4±0·1 nM) and skin (mean number 46·4±23·8 fmol mg⁻¹ protein, apparent dissociation constant 1 ± 0·2 nM) of clinically normal dogs. For clinically normal cats, approximately half these numbers of receptors with a lower affinity, were detected in liver (mean number 23·1±10·4 fmol mg⁻¹ protein, apparent dissociation constant 3·2±0·9 nM) and skin (mean number 23·90±10·9 fmol mg⁻¹ protein, apparent dissociation constant 2·2±1·5 nM). This difference between dogs and cats in [³H] dexamethasone binding receptors may contribute to the relative glucocorticoid resistance observed in cats.     

In vitro susceptibility of avian mycoplasmas to enrofloxacin, sarafloxacin, tylosin, and oxytetracycline.

In vitro susceptibility of avian Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) to enrofloxacin, sarafloxacin, tylosin, and oxytetracycline was determined by a serial broth dilution method. The minimum inhibitory concentration (MIC) was recognized by a conversion of the pH indicator phenol red in culture media to a yellow color. Each isolate or type strain of mycoplasma was tested in two replicates. The MICs of tylosin, enrofloxacin, sarafloxacin, and oxytetracycline against five isolates and two reference strains of MG (approximately 10(5) colony-forming units [CFU]/ml) were 0.05, 0.14, 0.37, and 1.30 microg/ml, respectively. The MICs of the four antimicrobial agents against six isolates and one reference strain of MS (approximate 10(5) CFU/ml) were 0.13, 1.82, 1.76, and 0.91 microg/ml, respectively. There were no differences (P > 0.05) between tylosin, enrofloxacin, and sarafloxacin against MG, but these three antibiotics were different (P < 0.05) from oxytetracycline. The MIC value of tylosin against MS was different (P < 0.05) from those of sarafloxacin and enrofloxacin, but it was not different (P > 0.05) from that of oxytetracycline.     

Pharmacokinetics of fluconazole in cats after intravenous and oral administration

Fluconazole (100 mg) was administered to six adult cats as an intravenous infusion over 30 minutes, and the same cats received 100 mg of the drug orally 16 weeks later. The cats were bled repeatedly through an indwelling jugular catheter, the plasma fluconazole concentrations were assayed by high performance liquid chromatography, and the concentration-time data were subjected to a non-compartmental pharmacokinetic analysis. The mean (SD) intravenous half-life (13·8 [2·6] hours) was similar to that observed after oral dosing (12·4 [3·0] hours). The plasma clearances (intravenous 0·9 [0·1], oral 0·9 [0·2] ml min⁻¹ kg⁻¹) and the volumes of distribution at steady state (intravenous 1·1 [0·1], oral 1·0 [0·1] litre kg⁻¹) were also similar after the two routes of dosing. The peak plasma concentration was reached 2·6 hours after oral dosing and the drug was completely bioavailable (1·09 [0·05]). On the basis of this single dose study, the administration of 50 mg fluconazole every eight hours to a 4 kg cat should produce average steady state plasma fluconazole concentrations of approximately 33 mg litre⁻¹.     

Comparative In Vitro Activity of 16 Antimicrobial Agents Against Actinobacillus Pleuropneumoniae

Sixteen antimicrobial agents were tested for their activity against 68 isolates of Actinobacillus pleuropneumoniae by determining the minimum inhibitory concentrations (MICs). Ceftiofur and the fluoroquinolones danofloxacin and enrofloxacin were the most active compounds, with a MIC for 90% of the isolates (MIC₉₀) of 0.05 µg/ml. The MIC₉₀ values of benzylpenicillin, amoxicillin and aspoxicillin were 0.78 units/ml, 0.39 µg/ml and 0.05 µg/ml, respectively. Three isolates (4.4%) were resistant to penicillins, but aspoxicillin was as active as ceftiofur against the susceptible isolates, with MICs of 0.05 µg/ml for all isolates. Resistance to oxytetracycline, chloramphenicol and thiamphenicol occurred in 22 (32.4%), 14 (20.6%) and 15 (22.1%) of the isolates, respectively. Doxycycline was more active than oxytetracycline, with a MIC₉₀ of 1.56 µg/ml as against 25 µg/ml. Florfenicol was not only as active as thiamphenicol, with a MIC for 50% of the isolates (MIC₅₀) of 0.39 µg/ml, but also active against thiamphenicol-resistant isolates. All the isolates were susceptible to florfenicol. All the isolates were also susceptible to gentamicin, spectinomycin, tilmicosin, colistin and tiamulin. Of these, spectinomycin was the least active, with a MIC₅₀ of 25 µg/ml, followed by tiamulin, with a MIC₅₀ of 6.25 µg/ml. Of the 68 isolates tested, 49 (72.0%) were of serotype 2; 14 (20.5%) were of serotype 1; 2 each (3.0$) were of serotypes 5 and 6; and one was of serotype 7. Of the isolates, 23 (33.8%) were resistant to one or more of the major antibiotics. Antibiotic resistance was found only infrequently among serotype 2, with 5 (10.2%) of 49 isolates being resistant to chloramphenicol and/or oxytetracycline, while it occurred in 18 (94.7%) of the 19 isolates of other serotypes.