An ultrasonographic scoring method for transabdominal monitoring of ascarid burdens in foals.

REASONS FOR PERFORMING STUDY: Parascaris spp. infections can lead to life-threatening small intestinal impactions in foals. Currently available diagnostic techniques cannot estimate the magnitude of an ascarid burden, and hence identify foals potentially at risk of developing impactions. OBJECTIVES: To describe and evaluate an ultrasonographic transabdominal scoring technique for monitoring of ascarid burdens in foals and to perform a cost-benefit analysis of the application of this technique. STUDY DESIGN: A transabdominal ultrasonographic technique was validated against ascarid worm counts from 10 foals aged 162-294 days. In a treatment trial, 15 foals were randomly allocated to 3 treatment groups: ivermectin, oxibendazole and no treatment. Blinded ultrasound examinations were performed daily for 5 consecutive days following treatment. Foals were examined ultrasonographically twice by the same investigator, and by different investigators for intra- and interobserver agreement evaluation. Cost-benefit analyses identified threshold values for the probability of ascarid impactions above which the screening method becomes cost-effective. METHODS: The ultrasound technique used 3 locations along the ventral midline. An ascarid scoring system was established that assessed the magnitude of ascarid burden ranging from 1-4. The method was validated against worm burdens of 10 worms and above with calculation of diagnostic specificity, sensitivity, and predictive values. Treatment trial data were evaluated statistically using mixed model analysis. Kappa values were generated for intra- and interobserver agreement. RESULTS: Two consecutive examinations were found to detect worm burdens >10 ascarids reliably. Ascarid scores declined in response to both anthelmintic treatments, although differences were not statistically significant. Kappa values indicated fair to moderate intra- and interobserver agreements. The majority of cost-benefit analyses indicated that ultrasound examinations are cost effective when the probability of ascarid impactions is above a range of 0.0001-0.0082 (i.e. 1 in 10,000 to 8 in 1000 foals). CONCLUSIONS: The ultrasonographic screening techniques can be a useful tool for monitoring ascarid burdens in foals.

Anthelmintic resistance in equine parasites--current evidence and knowledge gaps.

Anthelmintic resistance is becoming increasingly prevalent among equine nematode parasites. The first reports documenting resistance were published in the 1960s, just a short time after introduction of the first modern anthelmintics phenothiazine and thiabendazole. Several factors are known to influence development of resistance, but evidence specific to equine parasites is limited. Most current knowledge and applications have been extrapolated from research with trichostrongylid parasites of sheep. The number of cyathostomin species co-infecting horses adds to the complexity of investigating drug resistance but, given their apparent limited biological diversity, viewing these in a unispecific context remains a pragmatic approach. Factors affecting resistance development in cyathostomins include parasite seasonality, life span and fecundity, host immunity, and the existence of encysted stages. Further, parasite refugia have been shown to play a vital role in resistance development in other parasites, and likely is also important in equine parasites. Specific genetic factors for drug resistance and possible modes of inheritance have been identified for trichostrongylid nematodes, but it is widely accepted that several more remain undiscovered. Current evidence with equine and ruminant parasites suggests that fitness is not significantly compromised in drug resistant strains. Attempts to develop in vitro and molecular assays for diagnosing anthelmintic resistance in equine nematodes have had only limited success, standardized guidelines are sorely needed for performing the fecal egg count reduction test in horse populations. Taken together, this review illustrates the complexity of understanding anthelmintic resistance in equine nematodes, and emphasizes the need for further research.

Antimicrobial-associated diarrhoea in three equine referral practices.

REASONS FOR PERFORMING STUDY: Although antimicrobial-associated diarrhoea (AAD) is the most frequently observed adverse effect of antimicrobial therapy in horses, few multicentred studies on the prevalence of AAD have been performed. OBJECTIVES: To determine the prevalence of AAD in horses that developed diarrhoea after antimicrobial treatment for nondiarrhoeic conditions and identify the antimicrobials used. METHODS: The 2009 database of 3 referral hospitals was searched to identify nonhospitalised horses (weanling age or older) treated with antimicrobials for nongastrointestinal conditions. Horses with these criteria that presented with diarrhoea during 2009 were included in the study. Additional information, including antimicrobial administered and results of faecal pathogen testing, was gathered on each hospitalised case. RESULTS: Of the 5251 horses treated with antimicrobials for nongastrointestinal signs, 32 were diagnosed with probable AAD, a prevalence of 0.6% (95% confidence interval: 0.43-0.86%). The AAD-diagnosed horses had an 18.8% (6/32) mortality rate. Horses with AAD had been treated for an average of 4.2 days. The most frequently used antimicrobials in horses with AAD were gentamicin in combination with penicillin (n = 7), enrofloxacin (n = 7) and doxycycline (n = 4). Clostridium difficile was identified in faecal samples from 4 horses, 2 of which died and Salmonella from 3 horses. CONCLUSIONS: Results indicated that the prevalence of AAD is low. Any antimicrobial class commonly used in equine practice is a potential cause of equine AAD. Other risk factors, such as opportunistic enteropathogens, may play a part in the development of diarrhoea secondary to antimicrobial usage. POTENTIAL RELEVANCE: Although the risk of equine AAD is low, this sequela of antimicrobial treatment is possible especially when opportunistic enteropathogens or other risk factors are present. Because drugs from any antimicrobial class can be potentially involved in AAD, clinicians have additional incentive to ensure the judicious use of antimicrobial agents.

Plasma and pulmonary disposition of ceftiofur and its metabolites after intramuscular administration of ceftiofur crystalline free acid in weanling foals.

The objectives of this study were to determine the plasma and pulmonary disposition of ceftiofur crystalline free acid (CCFA) in weanling foals and to compare the plasma pharmacokinetic profile of weanling foals to that of adult horses. A single dose of CCFA was administered intramuscularly to six weanling foals and six adult horses at a dose of 6.6 mg/kg of body weight. Concentrations of desfuroylceftiofur acetamide (DCA) were determined in the plasma of all animals, and in pulmonary epithelial lining fluid (PELF) and bronchoalveolar lavage (BAL) cells of foals. After intramuscular (IM) administration to foals, median time to maximum plasma and PELF concentrations was 24 h (12-48 h). Mean (± SD) peak DCA concentration in plasma (1.44 ± 0.46 µg/mL) was significantly higher than that in PELF (0.46 ± 0.03 µg/mL) and BAL cells (0.024 ± 0.011 µg/mL). Time above the therapeutic target of 0.2 µg/mL was significantly longer in plasma (185 ± 20 h) than in PELF (107 ± 31 h). The concentration of DCA in BAL cells did not reach the therapeutic level. Adult horses had significantly lower peak plasma concentrations and area under the curve compared to foals. Based on the results of this study, CCFA administered IM at 6.6 mg/kg in weanling foals provided plasma and PELF concentrations above the therapeutic target of 0.2 µg/mL for at least 4 days and would be expected to be an effective treatment for pneumonia caused by Streptococcus equi subsp. zooepidemicus at doses similar to the adult label.

Pharmacokinetics of probenecid and the effect of oral probenecid administration on the pharmacokinetics of cefazolin in mares.

The pharmacokinetics and bioavailability of probenecid given IV and orally at the dosage level of 10 mg/kg of body weight to mares were investigated. Probenecid given IV was characterized by a rapid disposition phase with a mean half-life of 14.0 minutes and a subsequent slower elimination phase with a mean half-life of 87.8 minutes in 5 of 6 mares. In the remaining mare, a rapid disposition phase was not observed, and the half-life of the elimination phase was slower (172 minutes). The mean residence time of probenecid averaged 116 minutes for all 6 mares and 89.2 minutes for the 5 mares with biphasic disposition. The total plasma clearance of probenecid averaged 1.18 +/- 0.49 ml/min/kg, whereas renal clearance accounted for 42.6 +/- 9.3% of the total clearance. The steady-state volume of distribution of probenecid averaged 116 +/- 28.2 ml/kg. Plasma protein binding of probenecid was extensive, with 99.9% of the drug bound at plasma probenecid concentrations of 10 micrograms/ml. The maximum plasma probenecid concentration after 10 mg/kg orally averaged nearly 30 micrograms/ml. The half-life of probenecid after oral administration was approximately 120 minutes. Oral bioavailability was good with greater than 90% of the dose absorbed. The effect of probenecid on tubular secretion of organic anions was evaluated by determining the pharmacokinetics of IV cefazolin (11 mg/kg) administered alone and 15 minutes after probenecid (10 mg/kg orally). Treatment with probenecid did not affect pharmacokinetic values of cefazolin. This failure of probenecid to alter the pharmacokinetics of cefazolin may be caused by insufficient plasma probenecid concentrations after the oral dose.

Retrospective analysis of 29 fractures of the olecranon process of the equine ulna.

Twenty-nine fractures of the olecranon process of the ulna in horses treated at The Ohio State University College of Veterinary Medicine from 1973 through 1983 were evaluated. The objectives of the study were to determine the prognosis for various configurations of fractures of the olecranon process of the ulna, to determine what preoperative factors influenced the prognosis, and to evaluate the efficacy of the treatment methods used. The fractures were placed in one of 4 categories on the basis of severity of the injury: type-1 fractures involved the physeal plate; type-2 fractures involved the olecranon at the level of the anconeal notch (narrowest cross-sectional area of the ulna); type-3 fractures involved the proximal portion of the olecranon without involving the elbow joint; and type-4 fractures were severely comminuted fractures. Three modes of treatment used were: (1) open reduction and internal fixation, using a tension band plate, (2) elbow to ground splinting, with stall rest, and (3) stall rest alone. Internal fixation with a tension band plate was 68% successful. Of those horses in which repair was considered successful, 84% returned to excellent function. Elbow to ground splinting with stall rest was used successfully for nonarticular and nondisplaced fractures in 2 horses. Stall rest alone resulted in 28% "pasture sound" horses, with none of the 7 horses so treated returning to athletic performance. On the basis of this study, the following conclusions were derived. (1) Nonarticular/nondisplaced fractures are candidates for nonsurgical treatment, using full-limb splinting, stall rest, and periodic reevaluation.(ABSTRACT TRUNCATED AT 250 WORDS)

Surgical correction of angular limb deformities in foals: a retrospective study.

The outcome of surgical treatment of angular limb deformities in 29 foals was evaluated through long-term monitoring of athletic performance. Foals were placed into 1 of 2 groups, depending on the site of the angular limb deformity. In group 1 foals, the deformity involved the carpus of distal end of the radius. In group 2 foals, the deformity involved the distal end of the 3rd metacarpal or metatarsal bone. Group 1 contained 20 foals and group 2 contained 11 foals. Two foals were in both groups. Sixteen foals in group 1 and 4 foals in group 2 progressed to some form of athletic use. The underlying reasons for the failures in both groups was poor selection of cases and inappropriate surgical treatment.

Blood chemical abnormalities in cattle with ruptured bladders and ruptured urethras.

A study was undertaken to determine the blood chemical variables and compare changes that occurred with ruptured bladders and ruptured urethras in steers and yearling bulls. The fatality rates were 10.5% in steers with ruptured urethras and 50.8% in steers with ruptured bladders. Both groups had significantly decreased serum sodium and chloride values and significantly increased serum creatinine, blood urea nitrogen, and plasma protein concentrations compared to the normal group. Steers with ruptured bladders were more dehydrated, had significantly lower serum sodium and chloride values and had significantly higher blood urea nitrogen concentrations than steers with ruptured urethras. The combination of a decreased serum sodium, a decreased serum chloride, and a decreased ratio of serum phosphate to blood urea nitrogen occurred consistently within the ruptured bladder group. Of the variables examined, serum phosphate was the best prognostic indicator in the steers with ruptured bladders as all of the steers that died had a serum phosphate in excess of 2.9 mmol/L. The fluid and electrolyte changes are discussed.