Minimum inhibitory concentrations of equine Corynebacterium pseudotuberculosis isolates (1996-2012)

Background

Few studies report the minimum inhibitory concentrations for antimicrobials against equine Corynebacterium pseudotuberculosis isolates.

Hypothesis/Objectives

To evaluate trends in the in vitro activities of 20 antimicrobials against equine Corynebacterium pseudotuberculosis isolates from 1996 to 2012 and to determine if a relationship exists between the minimum inhibitory concentration (MIC) and location of the abscess.

Animals

Corynebacterium pseudotuberculosis isolates from 196 horses with naturally occurring disease.

Methods

Retrospective and cross‐sectional design. Medical records were reviewed to obtain clinical and MIC data. Minimum inhibitory concentrations were determined by the microdilution technique. The MIC results over 3 periods were compared (1996–2001, 2002–2006, 2007–2012).

Results

The MIC₉₀ values for clinically relevant antimicrobials were as follows: chloramphenicol ≤4 μg/mL, enrofloxacin ≤0.25 μg/mL, gentamicin ≤1 μg/mL, penicillin =0.25 μg/mL, rifampin ≤1 μg/mL, tetracycline ≤2 μg/mL, trimethoprim‐sulfamethoxazole (TMS) ≤0.5 μg/mL, ceftiofur =2 μg/mL, and doxycycline ≤2 μg/mL. There were no significant changes in MIC results over the study period. There was no relationship between MIC patterns and abscess location.

Conclusions and Clinical Importance

The MIC₅₀ and MIC₉₀ values of antimicrobials evaluated in this study for equine isolates of C. pseudotuberculosis did not vary over time. Abscess location was not associated with different MIC patterns in cultured isolates. Several commonly used antimicrobials are active in vitro against C. pseudotuberculosis in vitro.

Septic sialoadenitis in equids: a retrospective study of 18 cases (1998-2010)

REASON FOR PERFORMING STUDY

Septic sialoadenitis, although uncommonly reported in equids, is a significant cause of pain, inappetence, dysphagia and discomfort. There are currently few reported cases possibly as a result of its infrequent occurrence.

OBJECTIVES

To review cases presenting with sialoadenitis and describe the presenting complaints, results of diagnostic tests, treatment and outcome.

STUDY DESIGN

Retrospective case series.

METHODS

Records were reviewed for equids presenting to the UC Davis William R. Pritchard Veterinary Medical Teaching Hospital between 1998 and 2010 for salivary gland swelling. Equids were included if a diagnosis of septic sialoadenitis was made based on a combination of oral examination and/or ultrasonographic findings and/or microbial culture. Data collected included age, breed, presenting complaints, diagnostic results, treatment and outcome.

RESULTS

Eighteen equids were diagnosed with septic sialoadenitis affecting the parotid gland (11) or the mandibular salivary gland (7). Ultrasound was useful to differentiate whether the mandibular or parotid salivary gland was involved. Affected equids ranged in age from 4 to 30 years (mean 17.7 years). Fourteen of 15 (93.3%) equids that underwent a complete oral examination had dental or other oral abnormalities. Six of 18 cases had evidence of sialolithiasis. Culture of the infected salivary gland or secretions was performed in 9 equids and all yielded growth of Fusobacterium sp. along with other aerobic and anaerobic bacteria. Infection resolved in 15/18 cases (83.3%) and 2/18 (11.1%) were subjected to euthanasia.

CONCLUSIONS

Dental disease and sialolith formation may play important roles in the development of septic sialoadenitis in equids. Anaerobic infection should be assumed in all cases and affected horses should be treated for this until culture and sensitivity results are available. Prognosis is favourable (83.3%) with appropriate treatment.

Retrospective evaluation of crib-biting and windsucking behaviours and owner-perceived behavioural traits as risk factors for colic in horses

REASONS FOR PERFORMING STUDY

Although crib-biting (cribbing)/windsucking has previously been associated with 2 types of colic, additional research into the possible role of other behaviours on incidence of colic by type and severity has not been undertaken.

OBJECTIVES

To investigate: a relationship between cribbing/windsucking and colic; a relationship between cribbing/windsucking and different types of colic, both medical and surgical; and whether horses displaying specific behaviour traits were more likely to have had colic.

METHODS

A matched case-control retrospective study was conducted evaluating horses with various surgical and medical colic diagnoses, admitted to a referral hospital over a 3 year period. Computerised records and a validated internet questionnaire were used to obtain information on owner-perceived behavioural traits and repetitive behaviours.

RESULTS

Cribbing/windsucking was significantly associated with colic but was unassociated with one category or severity of colic over another. No other repetitive behaviour was associated with colic. Age (≥20 years) was significantly associated with colic. An anxious temperament was not associated with risk of colic.

CONCLUSION

Animals at higher risk for colic may be identified based on history of cribbing/windsucking behaviour, but this behaviour was unassociated with increased risk for a particular category or severity of colic. Horses characterised as being more anxious were not at increased risk for colic.

POTENTIAL RELEVANCE

There is a need to elucidate a causal relationship between cribbing/windsucking and gastrointestinal function as development of more effective and humane strategies to treat cribbing/windsucking behaviour may help to improve equine welfare and reduce the risk of colic.

Linkage of hyperkalaemic periodic paralysis in quarter horses to the horse adult skeletal muscle sodium channel gene

A genetic disease observed in certain Quarter horses is hyperkalaemic periodic paralysis (HYPP). This disease causes attacks of paralysis which can be induced by ingestion of potassium. Recent studies have shown that HYPP in humans is due to single base changes within the adult skeletal muscle sodium channel gene. A large Quarter horse pedigree segregating dominant HYPP was studied to determine if mutations of the sodium channel gene are similarly responsible for HYPP in horses. We used cross-species, PCR-mediated, cDNA cloning and sequencing of the horse adult skeletal muscle sodium channel alpha-subunit gene to identify a polymorphism, and then used this polymorphism to see if the horse sodium channel gene was genetically linked to HYPP in horses. The sodium channel gene was indeed found to be tightly linked to HYPP (LOD = 2.7, theta = 0). Our results suggest that HYPP in horses involves the same gene as the clinically similar human disease, and indicates that these are homologous disorders. The future identification of the specific sodium channel mutation causing HYPP in Quarter horses will permit the development of accurate molecular diagnostics of this condition, as has been recently shown for humans.

Immunological response to long-term transport stress in mature horses and effects of adaptogenic dietary supplementation as an immunomodulator

REASONS FOR PERFORMING STUDY

Little information exists on the immunological effects of transport or the use of supplements to minimise transport stress.

OBJECTIVES

To establish baseline ranges and evaluate immunophenotypic and functional changes associated with transport and a nutritional 'adaptogen' supplement.

METHODS

Horses received either supplement (n = 10) or placebos (n = 9) during the 30 day study. After 28 days in stalls, 12 horses (6 supplement; 6 placebo) were transported for 24 h, then unloaded and recovered. Venous blood samples were collected on Days 1, 14 and 28 to establish baselines, and on Days 28, 29 and 30 to examine changes during transport and recovery.

RESULTS

Transport prompted elevations (P<0.05) in cortisol concentration, neutrophil count and white blood cell counts, while lymphocyte subpopulation counts (CD3+, CD4+, CD8+, CD21+) decreased (P<0.05). Normal phenotypic lymphocyte profiles returned within 24 h of recovery. Supplement effects on immunophenotype (CD21+ and CD8+) were observed in stabled horses (P<0.05), but not in transported horses.

CONCLUSIONS

These results provide insights into the immunological mechanisms associated with long-term transport.

POTENTIAL RELEVANCE

The existence of a small window of immunological uncertainty follows long-term transportation, enhancing the potential risk of infectious disease in susceptible individuals.

Evaluation of the SNAP foal IgG test for the semiquantitative measurement of immunoglobulin G in foals

The SNAP Foal IgG test (IDEXX) as evaluated for its accuracy and usefulness by measuring blood samples collected from 42 foals between 24 and 48 hours after birth. The results were compared with the single radial immunodiffusion (SRID) test as the reference method. The SNAP test was quick and easy to perform, and the results were similar to those obtained by SRID in 64 per cent of the samples. The best results were found with low (< 400 mg/dl) and high (> 800 mg/dl) concentrations of immunoglobulin G, with an accuracy of 80 per cent and 89 per cent, respectively. The intermediate concentrations were usually lower when measured by the SNAP test than by the SRID test, possibly owing to the variable volume of blood added to the test with the sample loop.

Evaluation of peritoneal fluid pH, glucose concentration, and lactate dehydrogenase activity for detection of septic peritonitis in horses

OBJECTIVE

To determine whether peritoneal fluid pH, glucose concentration, and lactate dehydrogenase activity can be used to differentiate horses with septic peritonitis from those with nonseptic peritonitis.

DESIGN

Prospective study.

ANIMALS

46 horses, including 10 healthy horses, 15 horses with septic peritonitis, and 21 horses with nonseptic peritonitis.

PROCEDURE

Peritoneal fluid and blood samples were analyzed for pH, glucose concentration, and lactate dehydrogenase activity. Complete blood cell counts were performed, and peritoneal fluid samples were submitted for bacterial culture.

RESULTS

Horses with septic peritonitis had significantly lower peritoneal fluid pH and glucose concentrations than horses with nonseptic peritonitis and healthy horses. Compared with other tests, serum-to-peritoneal fluid glucose concentration differences > 50 mg/dl had the highest diagnostic use for detection of septic peritonitis. Peritoneal fluid pH < 7.3, glucose concentration < 30 mg/dl, and fibrinogen concentration > 200 mg/dl were also highly indicative of septic peritonitis.

CLINICAL IMPLICATIONS

Peritoneal fluid pH and glucose concentration can be used to assist in the identification of horses with septic peritonitis. These measurements can provide an early indication of sepsis, especially if cytologic evaluation of peritoneal fluid is unavailable or results are equivocal and peritoneal fluid bacterial culture results are pending.

Comparative molecular characterization of Corynebacterium pseudotuberculosis of different origin

Ribotyping and susceptibility to 17 antimicrobial agents were used to compare 37 isolates of Corynebacterium pseudotuberculosis (28 from horses, 1 from cattle, 3 from sheep and 5 from goats) derived from various types of lesions, and different geographic locations. According to the presence of nitrate reductase, all but one isolate from horses reduced nitrate (nitrate-positive), whereas all isolates from sheep and goats were unable to reduce nitrate (nitrate-negative). The ribotype of the nitrate-negative isolate from a horse with ulcerative lymphangitis was identical to all the other isolates from horses, and different than the ribotype of nitrate-negative isolates from sheep and goats. Ribotyping with one of the restriction endonucleases, Apa 1, revealed differences between, but not within, the two biotypes. However, ribotyping with Pst 1 endonuclease revealed one variant within the equine biotype and one variant within the ovine biotype. The minimum inhibitory concentration (MIC; microgram/ml) of antimicrobial agents against isolates from nitrate-negative and nitrate-positive groups was very similar, with the exception of isolates from sheep and goats which had a higher MIC for amikacin than isolates from horses and cattle.

A clinical trial of probiotic administration for prevention of Salmonella shedding in the postoperative period in horses with colic

The purpose of this study was to evaluate the effects of probiotic administration on the prevalence of fecal shedding of Salmonella, the prevalence of postoperative diarrhea, the length of antimicrobial therapy, and the length of the hospitalization stay during the postoperative period in horses with colic. Two commercially available probiotics for horses were used in a double-blind prospective study of 200 horses undergoing surgery for colic. Probiotic or placebo was administered PO once a day for 7 days postoperatively, and fecal cultures for Salmonella were obtained daily for 10 days. After selection of 186 patients completing the treatment protocol, the results indicated that the commercial probiotic formulations had no effect on Salmonella shedding, prevalence of diarrhea, length of antimicrobial therapy, or length of hospitalization (P > .05). Twenty percent of the horses yielded 1 or more positive fecal cultures for Salmonella; of these horses, 74% were classified as asymptomatic shedders. Twenty-six percent of all horses had fluid diarrhea postoperatively, with only 12% of these horses having positive fecal cultures for Salmonella. The most common isolate was Salmonella krefeld (24 of 39 isolates). Among the different gastrointestinal disorders, horses with feed and sand impactions appeared to be more prone to shed Salmonella.

Laryngeal and pharyngeal dysfunction in horses homozygous for hyperkalemic periodic paralysis

OBJECTIVE

Evaluate histories, clinical signs, and laboratory data of 69 horses homozygous by DNA testing for hyperkalemic periodic paralysis (HPP).

DESIGN

Cohort study.

SAMPLE POPULATION

69 of 189 horses testing homozygous for HPP between October 1992 and November 1994.

PROCEDURE

Questionnaires addressing signalment, training regimes, medical history, and current status of affected horses were sent to owners, trainers, or attending veterinarians. Data from completed questionnaires were tabulated and evaluated, using descriptive statistics.

RESULTS

Sixty-nine (37%) of 189 questionnaires were completed and returned. Clinical episodes of muscle weakness or paralysis varied in severity and frequency from mild muscle fasciculations to recumbency and death. Sixty-three of 68 HPP-affected horses were reported to have had stridor associated with exercise, excitement, stress, or episodes of muscle paralysis. Common endoscopic findings in affected horses included pharyngeal collapse, pharyngeal edema, laryngopalatal dislocation, and laryngeal paralysis. Twelve of 27 horses receiving acetazolamide had decreases in stridor while receiving medication.

CLINICAL IMPLICATIONS

Most horses testing homozygous for HPP had clinical signs associated with pharyngeal and laryngeal dysfunction. Hyperkalemic periodic paralysis should be included on a differential list for horses examined for signs of laryngeal or pharyngeal dysfunction or stridor. Treatment with acetazolamide may help to control respiratory tract signs associated with this disease.

Corynebacterium pseudotuberculosis infection in horses: 538 cases (1982-1993)

OBJECTIVE

To describe clinical manifestations of Corynebacterium pseudotuberculosis infection in horses and to evaluate diagnostic methods for identification of this disease.

DESIGN

Retrospective case series.

ANIMALS

538 horses with a diagnosis of C pseudotuberculosis infection.

RESULTS

Median age of horses with external abscesses was similar to that in horses with internal abscesses. Breed and sex did not appear to be associated with infection. Cases were detected during all 12 months; however, the disease was most common in the fall and early winter, with the highest incidence in September, October, and November in every year. Most horses (492/538, 91.4%) had a single episode of infection, without recurrence in subsequent years. Of 538 horses, 308 had pectoral abscesses, although infection was documented in many other anatomic locations. Forty-two horses had internal abscesses involving the abdomen or thoracic cavity. Corynebacterium pseudotuberculosis infection was readily identified by bacterial culture of aspirate samples from abscesses. The synergistic hemolysis inhibition test was useful for diagnosis of internal abscesses; however, it was unreliable for the diagnosis of external abscesses. Horses with external abscesses responded well to conventional treatment, in contrast to those with internal abscesses. The overall case fatality was low (3.9%), and was considerably lower for horses with external abscesses (0.8%) than for horses with internal abscesses (40.5%).

CLINICAL IMPLICATIONS

Serology (synergistic hemolysis inhibition titers > or = 512) is useful for diagnosis of internal abscesses, but not reliable for diagnosis in horses with external abscesses. Prognosis for horses with internal abscesses is considerably poorer than for those with external abscesses.

Pathophysiology of sodium channelopathies: correlation of normal/mutant mRNA ratios with clinical phenotype in dominantly inherited periodic paralysis

It is often suggested that polygenic or environmental factors are responsible for clinical variability between patients with identical mutations. However, most dominant diseases are caused by a change-of-function alteration in the mutant allele's protein product. All patients are heterozygous and presumably express both mutant and normal proteins from the corresponding genes. Thus, a possible molecular mechanism for clinical variability could be the difference in relative levels of mutant vs. normal mRNA in different patients with the same mutation. To investigate this hypothesis, it is necessary to have access to a series of tissue biopsies from many patients with the same mutation causing a clinically variable dominant disease. Human hyperkalemic periodic paralysis (HyperPP) has been shown to be a clinically variable disorder caused by change-of-function mutations of the skeletal muscle sodium channel protein. We recently identified a large (> 50,000) pedigree of affected Quarter Horses sharing the same causative amino acid alteration of the muscle sodium channel protein. The horses like humans show substantial clinical variability. In this report, we developed a fluorescent reverse transcription-polymerase chain reaction assay which quantifies the relative levels of normal and mutant mRNA expression of the horse adult skeletal muscle sodium channel gene in affected Quarter Horses. We found that asymptomatic horses showed more normal sodium channel mRNA, while moderately affected horses showed more mutant mRNA. The ratios of mutant/normal mRNA between these two groups are statistically different, suggesting that severity of HyperPP Quarter Horses may indeed be correlated to the ratio of mutant and normal sodium channel gene expression in skeletal muscle.

Salmonellosis

Salmonellosis is the most common infectious cause of diarrhea or colitis in horses. It can be associated with high fatality rates in patients with compromised host defenses. The increasing incidence of infection and antimicrobial resistance present a challenge for the practicing veterinarians. The epidemiology and pathogenesis of salmonellosis are reviewed. Diagnosis, treatment, and control of disease are discussed.

[3H]ouabain binding in skeletal muscle from horses with hyperkalemic periodic paralysis

Ouabain, a cardiac glycoside, binds to the Na(+)-K(+)-adenosine triphosphatase (Na+ pump) and prevents active transport of Na+ and K+ across cell membranes. We used [3H]ouabain to quantify the number and affinity of Na+ pumps in skeletal muscle from Quarter Horses with the muscular disorder hyperkalemic periodic paralysis (HYPP). [3H]Ouabain-binding properties of gluteal muscle from clinically normal and affected horses were used to determine whether altered Na+ pump number or affinity could contribute to the pathologic features of muscle in affected horses. Foals and adult horses with HYPP were compared with age-matched clinically normal horses. The number of [3H]ouabain-binding sites in adult gluteal muscle was not different between the 2 types of horses (85.7 +/- 8.9 pmol of [3H]ouabain-binding sites/g [wet muscle weight] in horses with HYPP vs 100.2 +/- 8.8 pmol/g in clinically normal adult horses). Gluteal muscles in HYPP-affected and clinically normal foals also contained a similar number of [3H]ouabain-binding sites (222.3 +/- 21.0 pmol/g vs 225.3 +/- 24.2 pmol/g, respectively). The affinity of these binding sites for ouabain was not different, between adults or foals, in clinically normal or affected horses. Our results indicate that membrane events underlying the periodic episodes of paralysis in horses with HYPP are not attributable to quantitative changes in Na+ pump number or affinity. Our data cannot exclude the possibility that the specific activity of the Na+ pump is altered in muscle from HYPP-affected horses.

Genetic study of hyperkalemic periodic paralysis in horses

Four Quarter Horses (1 stallion, 3 mares) with hyperkalemic periodic paralysis were mated to unaffected horses to determine the genetic basis of the disease. The affected stallion was bred to 11 unaffected mares (4 Quarter Horses, 1 Arabian, 2 Standardbreds, and 4 Thoroughbreds). The 3 affected mares were bred to an unaffected Quarter Horse stallion. Of the 15 offspring obtained from these matings, 9 were affected with hyperkalemic periodic paralysis, and 6 were unaffected, consistent with an autosomal dominant mode of inheritance. Diagnosis was established by results of oral administration of potassium chloride and demonstration of characteristic clinical signs accompanied by hyperkalemia. Oral administration of potassium chloride resulted in marked increases in plasma potassium concentrations in affected and unaffected foals, although hyperkalemia was associated with clinical signs of hyperkalemic periodic paralysis in the affected foals. Evaluation of blood samples from affected and unaffected offspring revealed no linkage with erythrocyte and serum markers at 24 loci.

Sodium Channelopathies: Dramatic Diseases Caused

Very recently, the first vertebrate genetic diseases caused by abnormal voltage-sensitive channels have been found in humans and horses: single amino acid changes within the 1,700-amino acid adult skeletal muscle sodium channel result in potassium-induced muscle paralysis or cold-induced muscle contraction.

Ionized calcium concentration in horses with surgically managed gastrointestinal disease: 147 cases (1988-1990)

Packed cell volume, total plasma protein, serum sodium, potassium, and ionized Ca2+ concentrations, and blood pH were determined at the time of admission and following surgery in 147 horses with acute abdominal crisis. Horses were allotted to 3 categories on the basis of the surgical lesion: (1) nonstrangulating obstruction of the ascending or descending colon (category A, n = 76), (2) strangulating and nonstrangulating infarction of the cecum or ascending colon (category B, n = 37), and (3) strangulating and nonstrangulating infarction of the small intestine (category C, n = 25). Horses with low serum ionized Ca2+ concentration following surgery were given 23% calcium gluconate (100 to 300 ml) IV to effect, and ionized Ca2+ concentration was determined following treatment. The serum ionized Ca2+ concentrations of horses in categories A, B, and C before and after surgery were lower than our normal laboratory reference range. Prior to surgery, serum ionized Ca2+ concentration measured from horses in category B and C was lower than that in horses in category A. There was no difference in ionized Ca2+ concentration in serum samples obtained before surgery in horses from category B and C, and in serum samples obtained following surgery. There was a decrease in ionized Ca2+ concentration during surgery in horses in category A. There was no change between preoperative and postoperative ionized Ca2+ concentration in the samples obtained from horses in category B and C. After calcium gluconate administration, all horses with low serum ionized Ca2+ after surgery had concentrations within our normal range. Measurement of serum ionized Ca2+ in horses with an acute abdominal crisis is recommended.(ABSTRACT TRUNCATED AT 250 WORDS)

Periodic paralysis in quarter horses: a sodium channel mutation disseminated by selective breeding

We recently reported on a linkage study within a Quarter Horse lineage segregating hyperkalaemic periodic paralysis (HYPP), an autosomal dominant condition showing potassium-induced attacks of skeletal muscle paralysis. HYPP co-segregated with the equine adult skeletal muscle sodium channel alpha subunit gene, the same gene that causes human HYPP. We now describe the Phe to Leu mutation in transmembrane domain IVS3 which courses the horse disease. This represents the first application of molecular genetics to an important horse disease, and the data will provide an opportunity for control or eradication of this condition.

Effect of calf age and Salmonella bacterin type on ability to produce immunoglobulins directed against Salmonella whole cells or lipopolysaccharide

A commercially available Salmonella bacterin was administered to Holstein calves starting at 1 to 19 weeks of age. Serum samples were obtained before administering bacterin and at 2-week intervals thereafter. An ELISA with Salmonella dublin lipopolysaccharide (LPS) or S dublin whole cells as antigen, was used to measure specific IgG and IgM responses. Antibody responses to LPS were not detected from calves < 12 weeks old inoculated with killed bacterin. Immunoglobulin responses to whole-cell antigen were detected from all age groups of calves inoculated with the same killed Salmonella bacterin. Calves < 11 weeks old are able to produce immunoglobulins to some whole-cell antigens, but are unable to produce anti-LPS immunoglobulins when inoculated with killed Salmonella bacterin. This age-related response to killed Salmonella antigens may account, in part, for increased susceptibility to salmonellosis in calves < 12 weeks old. In comparison to the response for killed antigen, 8 calves given modified-live aromatic-dependent S dublin bacterin at 1 to 3 weeks of age had detectable anti-LPS immunoglobulins after immunization, although the response was not as rapid and was of a lesser magnitude than that of older calves given killed Salmonella bacterin.

Persistent experimental Salmonella dublin intramammary infection in dairy cows

Experimental intramammary infections were induced in five post-parturient Holstein cows by inoculation of low numbers (5000 colony forming units) of virulent Salmonella dublin via the teat canal of mammary gland quarters. Rectal temperature, pulse and respiratory rates, milk yield, and milk quality as assessed by the California Mastitis Test (CMT) and somatic cell counts (SCC) were recorded every 12 hours at milking. Bacteriologic cultures of foremilk quarter samples and feces were obtained daily, as were complete blood counts. ELISA titers for IgG and IgM recognizing S. dublin lipopolysaccharide (LPS) were obtained weekly on serum and quarter milk samples. All cows excreted S. dublin intermittently from infected quarters, but no changes were detected in rectal temperature, appearance of the mammary gland or secretions, CBC, milk yield, and pulse and respiratory rates. Somatic cell counts were modestly increased in infected quarters as compared with uninfected quarters (P = .015, paired t test); however, CMT scores after infection remained low, and were not significantly different from pre-infection scores (P greater than .10, sign test). After infection, administration of dexamethasone resulted in signs of clinical mastitis and increased excretion of S. dublin from mammary quarters (P = .0004, paired t test). One cow had necrotizing mastitis and S. dublin septicemia and was euthanatized. In the four surviving cows, clinical improvement was observed after systemic gentamicin therapy and intramammary infusion with polymyxin B, but all cows continued to excrete S. dublin intermittently from one or more quarters and occasionally from feces for the remaining period of observation. All infected cows demonstrated a rise in IgG and IgM ELISA titers recognizing S. dublin LPS in serum and milk. At necropsy (13-25 weeks postinfection), S. dublin was recovered only from the mammary tissue or supramammary lymph nodes in three of four cows. In one cow, mammary gland and lymph-node samples were negative for S. dublin despite positive milk cultures. In all cows, histopathologic examination revealed multifocal areas of chronic active mastitis. These lesions were similar to histopathologic findings from mammary gland carriers with naturally acquired S. dublin infection.

Altered ionic permeability in skeletal muscle from horses with hyperkalemic periodic paralysis

A recently described disorder in certain registered Quarter horses bears many clinical similarities to the muscle disease identified as hyperkalemic periodic paralysis (HPP) in humans. Pathological changes in membrane permeability or Na(+)-K+ pump activity have been proposed to produce the muscle depolarization and inexcitability that characterize the condition in humans. Biopsies of external intercostal muscle from normal and affected horses were used to determine whether alterations in either permeability and/or pump activity could be linked to the pathology in horses. Affected horse muscle is approximately 16 mV more depolarized than normal muscle at rest, and the muscle membrane potential of HPP horses is less responsive to changes in extracellular K+. Calculation of the relative membrane permeabilities of Na+ and K+ (PNa/PK) indicates that this ratio is significantly increased in HPP muscle. The increase is probably due to an increase in PNa rather than to a decrease in PK, since addition of 10(-6) M tetrodotoxin produces an approximately 14-mV membrane hyperpolarization in HPP fibers but is without effect in normal fibers. The clinical similarities between HPP in horses and humans suggest a common genetic defect in the two species.

Use of ELISA for detection of immunoglobulins G and M that recognize Salmonella dublin lipopolysaccharide for prediction of carrier status in cattle

Immunoglobulin reactions to Salmonella dublin in serum and milk from 4 groups of lactating cows were measured by an indirect ELISA. The groups consisted of (1) cows that were natural carriers of S dublin in the mammary gland, (2) experimentally infected cows that did not become carriers, (3) cows inoculated with a commercial S dublin bacterin, and (4) cows used as S dublin-negative controls. Milk and serum samples were obtained at monthly intervals. Models for predicting carrier status were developed by use of stepwise logistic regression. Independent variables consisted of serum and milk IgG and IgM titers to S dublin lipopolysaccharide and a ratio of IgG to IgM. The utility of a single sample vs multiple samples obtained at 1-month or 2-month intervals was tested by comparison of goodness-of-fit chi 2 P values for 8 models predicting carrier status. Immunoglobulin reactions specific to S dublin were a significant predictor of carrier status (P less than 0.001). Serum IgG titers specific for S dublin were the most important variable for predicting carrier status. Two serum IgG titers to S dublin obtained 2 months apart was a better predictor of carrier status than measurement of the IgG:IgM ratio from a single serum sample. Immunoglobulin recognizing S dublin epitopes also were detected in milk samples. In milk, performing 2 ELISA 60 days apart to determine IgG and IgM reactions to S dublin appeared to be useful for the prediction of carrier status, but was not as accurate as models for serum immunoglobulin reactions.

Hyperkalemic periodic paralysis in horses

Eleven horses (3 mares, 7 stallions, 1 gelding) with clinical and biochemical evidence of hyperkalemic periodic paralysis were studied. Each horse had history of episodic weakness, muscular tremors, or collapse, which lasted for periods of a few minutes to hours. Diagnosis was based on hyperkalemia in association with a spontaneous episode of paralysis or by precipitation of an episode by oral administration of potassium chloride. Clinical and biochemical events were documented during spontaneous and induced episodes of muscular weakness. During episodes, electrocardiographic findings were consistent with hyperkalemia. Electromyography performed between episodes revealed fibrillation potentials and positive sharp waves, complex repetitive discharges, and myotonic discharges. Histologic changes in muscle biopsy specimens varied from no overt changes in some horses to vacuolation in type-2B fibers with mild degenerative changes in other horses. Electron microscopy of myofibers revealed dilatations of the sarcoplasmic reticulum. Analysis of blood samples taken serially during induced attacks in 5 horses revealed marked hyperkalemia (5.5 to 9.0 mEq/L), with normal acid-base status, hemoconcentration, and modest changes in muscle-derived enzymes. Close correlation (r2 = 0.882) between total plasma protein and plasma potassium concentrations was observed and indicated a shift of fluid out of the extracellular fluid compartment. Treatment of either spontaneous or induced episodes by IV administration of calcium, glucose, or bicarbonate resulted in rapid recovery. Dietary management or daily administration of acetazolamide effectively controlled episodes. An affected mare was bred to an affected stallion, and 3 affected offspring were produced by embryo transfer. Blood samples from another extended family of affected horses were analyzed for identification of a genetic marker.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunity targeting common core antigens of gram-negative bacteria

Antibodies against common gram-negative core antigens can provide protection against environmental, commensual, and contagious bacteria that cause life-threatening gram-negative sepsis/endotoxemia. Cross-protective immunity may be effective against many common livestock diseases, including neonatal coliform septicemia, coliform mastitis, septic metritis, and severe enteritis. The greatest potential benefit of cross-protective immunity may be realized in the reduction of ill-thrift and mortality of neonates. The use of active and passive immunization against core antigens common to gram-negative bacteria has been successful in human beings, laboratory animals, and livestock. Protection has been observed following challenge with either heterologous endotoxin or unrelated, live, virulent gram-negative bacteria.

Strangulating volvulus of the ascending colon in horses

Of 57 horses with strangulating volvulus of the ascending colon, 42 were mares (including 21 postparturient mares), 8 were stallions, and 7 were geldings. Volvulus occurred most frequently in the summer (n = 24) and spring (n = 17). Pain was evaluated as severe in 41 horses, moderate in 9, and mild in 4. The abdominal fluid from 30 horses varied from clear yellow in 19 horses, to cloudy yellow in 3 horses, and serosanguineous in 8 horses. Protein content and nucleated cell count in the abdominal fluid were 2.5 +/- 1 g/dl and 1,000 +/- 900 microliters, respectively. Fifty horses had greater than or equal to 360 degrees volvulus and 7 had a 270 degrees volvulus, with 49 occurring in a counterclockwise direction. The site of volvulus in all horses was at the mesenteric attachment of the colon, except for a 360 degrees volvulus at the sternal and diaphragmatic flexures in 1 horse. Survival rates for horses with a greater than or equal to 360 degrees and a 270 degrees volvulus were 36% and 71%, respectively. The difference in survival rates reflected the severe vascular occlusion in the colon of horses with greater than or equal to 360 degrees volvulus. In nonsurvivors, hemorrhage in the submucosa and lamina propria (P less than 0.005) and edema in the submucosa (P less than 0.01) were greater than those in survivors. In nonsurvivors, greater than 97% of the superficial epithelium was lost. In horses that survived, only 60% of the cells were lost or degenerated.(ABSTRACT TRUNCATED AT 250 WORDS)

Compensatory weight gain in steers recovered from oak bud toxicosis

Cattle that had recovered from clinical oak bud toxicosis (as assessed by normal BUN and serum creatinine values and good appetite) performed better than did clinically normal herdmates when weight gain and feed efficiency were compared. Both groups had a rate of weight gain (oak bud-exposed cattle, 1.76 kg/steer/d; control cattle, 1.57 kg/steer/d) that exceeded the feedlot mean value (approximately 1.4 kg/d) for cattle (of similar starting weight and diet) that had zeranol implants, and the difference was significant (P less than 0.005) for both groups. The difference in weight gain performance of oak bud-exposed cattle, compared with control cattle, was not highly significant; however, the improved feed efficiency was significantly (P less than 0.05) better than that in controls (2.57 kg of feed/kg of weight gain vs 3 kg of feed/kg of weight gain). On the basis of accepted criteria (increased rate of weight gain and efficiency of feed conversion), the group of oak bud-exposed cattle of this study had compensatory weight gain. Thus, cattle with good evidence of clinical recovery from oak bud toxicosis can be expected to perform in the feedlot at least as well as cattle not exposed to oak bud toxicosis, and may have compensatory weight gain.

Perioperative medical care for equine abdominal surgery

Rational perioperative management improves the success rate of abdominal surgery. Important aspects of management are discussed, including principles of fluid therapy, nutrition, intravenous catheterization, antimicrobial prophylaxis, and the use of nonsteroidal anti-inflammatory medication. Current advances in the area of immunotherapy are mentioned.

Protection against clinical endotoxemia in horses by using plasma containing antibody to an Rc mutant E. coli (J5)

Thirty-two horses with clinicopathologic evidence of endotoxic shock were randomly selected for a double-blind trial of hyperimmune lipopolysaccharide (LPS) core antigen plasma. Horses were suffering from acute toxic enteritis (n = 15), 360 degrees volvulus of the large colon (n = 9), proximal jejunitis/duodenitis (n = 6), or strangulating obstruction of the small intestine (n = 2). Plasma was harvested from suitable equine plasma donors (preimmune plasma) and horses were immunized with a whole-cell bacterin of an Rc mutant E. coli (J5). Plasma was again harvested from these horses when IgG ELISA titers recognizing LPS core antigen were greater than 1:32,000. All horses included in the trial received either preimmune or hyperimmune plasma in addition to traditional therapy (fluids, antimicrobials, antiinflammatory agents, etc.) as dictated by the attending clinician. The mortality rate in the group of horses receiving hyperimmune plasma was 13%; in the control group receiving preimmune plasma, the mortality rate was 47% (P = .045). Horses receiving J5 hyperimmune plasma had a significantly improved clinical appearance 48 hours after plasma administration (P less than .05) and a shorter period to recovery than control horses (P = .069).

Oak toxicosis in cattle in northern California: clinical and pathologic findings

Sixteen calves (3 to 8 months old) affected with oak toxicosis were studied. Clinical, laboratory, and pathologic findings during the peracute through chronic stages were documented. Of the calves studied, 1 died, and 9 others were euthanatized because death was imminent. To evaluate chronic effects, the 6 remaining cattle were euthanatized after 2 months. One calf with acute toxicosis was treated successfully with diuretics and fluid volume replacements containing sodium chloride and calcium. Clinical and laboratory data were compared between survivors and nonsurvivors. A statistically significant (P less than 0.02) difference was found only in serum creatinine concentration at the time of initial reexamination. A decrease in BUN and creatinine values during the next 7 days and the lack of anorexia after the acute phase were the best prognostic indicators for survival.

Acute myelomonocytic leukemia in a horse

A 7-year-old Quarter Horse stallion with a myeloproliferative disorder was examined because of colic, and an enterolith was removed surgically. The horse experienced secondary complications after abdominal surgery, and leukopenia and thrombocytopenia were detected. Five months later, the horse was examined for recurrent peripheral edema and for repair of an abdominal incisional hernia. Acute myelomonocytic leukemia was diagnosed, and treatment with low-dose (noncytocidal) cytosine arabinoside was unsuccessful. Necropsy revealed neoplastic infiltrate in the spleen, liver, lung, adrenal gland, testes, and eye. The persistent hematologic abnormalities before the onset of overt leukemia may represent hematopoietic dysplasia or preleukemia.