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Abstract

Objective—To describe shiga-toxigenic Escherichia coli O157:H7 (STEC O157:H7) fecal shedding prevalence, seasonal fecal shedding patterns, and site-specific prevalence from the oral cavity, skin, and feces of dairy cattle.

Design—Cross-sectional study.

Animals—Adult dairy cattle from 13 herds in Louisiana.

Procedure—Samples were cultured for STEC O157 by use of sensitive and specific techniques, including selective broth enrichment, immunomagnetic separation, monoclonal antibody-based O:H enzyme immunoassay serotyping, and polymerase chain reaction virulence gene characterization. Point estimates and 95% confidence intervals were calculated for fecal shedding prevalence as well as site-specific prevalence from the oral cavity, skin, and feces. Logistic regression was used to assess seasonal variation and differences at various stages of lactation with respect to fecal shedding of STEC O157 in cattle sampled longitudinally.

Results—Summer prevalence in herds (n = 13) was 38.5%, with a cow-level prevalence of 6.5%. Among positive herds, prevalence ranged from 3% to 34.6%. Samples from 3 of 5 herds sampled quarterly over 1 year yielded positive results for STEC O157. In herds with STEC O157, an increase in cow-level prevalence was detected during spring (13.3%) and summer (10.5%), compared with values for fall and winter. Site-specific prevalences of STEC O157:H7 from oral cavity, skin, and fecal samples were 0%, 0.7%, and 25.2%, respectively.

Conclusions and Clinical Relevance—Our data indicated that STEC O157:H7 was commonly isolated from dairy cows in Louisiana, seasonally shed, and isolated from the skin surface but not the oral cavity of cows. (J Am Vet Med Assoc 2004;224:1151–1158)

Full access
in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Summary

Three doses of an α2-adrenoreceptor antagonist, atipamezole, were administered to reverse xylazine-induced sedation, bradycardia, and ruminal atony in calves. Once a week for 4 weeks, each of 6 calves was administered iv 1 treatment of: 0.3 mg of xylazine/kg of body weight, followed in 10 minutes by 1 ml of 0.9% NaCl; 0.3 mg of xylazine/kg, followed in 10 minutes by 3 μg of atipamezole/kg; 0.3 mg of xylazine/kg, followed in 10 minutes by 10 μg of atipamezole/kg; or 0.3 mg of xylazine/kg, followed in 10 minutes by 30 μg of atipamezole/kg. The order of the 4 treatments in each calf was selected at random. Xylazine alone caused lateral recumbency for 33.6 ±7.1 minutes (mean ± sem-). Atipamezole administered at dosages of 3, 10, and 30 μg/kg shortened xylazine-induced lateral recumbency to 20.5 ± 3.0, 10.2 ± 0.2, and 9.3 ± 0.5 minutes, respectively. Calves given xylazine alone stood at > 60 minutes after the onset of recumbency. Atipamezole given at 3, 10, and 30 μg/kg shortened the time from onset of lateral recumbency to standing to 40.2 ± 6.9, 12.8 ± 1.1, and 10.0 ± 0.7 minutes, respectively. Drowsiness was found in calves given the lowest dosage of atipamezole (3 μg/kg) after the calves stood.

Atipamezole given at dosages of 10 and 30 μg/kg reversed xylazine-induced ruminal atony in a dose-dependent manner. In addition, 30 μg of atipamezole/kg reversed xylazine-induced bradycardia, but the lower dosages of this antagonist did not. Results indicated that 30 μg of atipamezole/kg should be a useful antidote for xylazine overdose in cattle.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether the basis for recurrent exertional rhabdomyolysis (RER) in Thoroughbreds lies in an alteration in the activation and regulation of the myofibrillar contractile apparatus by ionized calcium.

Animals—4 Thoroughbred mares with RER and 4 clinically normal (control) Thoroughbreds.

Procedure—Single chemically-skinned type-I (slowtwitch) and type-II (fast-twitch) muscle fibers were obtained from punch biopsy specimens, mounted to a force transducer, and the tensions that developed in response to a series of calcium concentrations were measured. In addition, myofibril preparations were isolated from muscle biopsy specimens and the maximal myofibrillar ATPase activity, as well as its sensitivity to ionized calcium, were measured.

Results—Equine type-I muscle fibers were more readily activated by calcium than were type-II muscle fibers. However, there was no difference between the type-II fibers of RER-affected and control horses in terms of calcium sensitivity of force production. There was also no difference between muscle myofibril preparations from RER-affected and control horses in calcium sensitivity of myofibrillar ATPase activity.

Conclusion and Clinical Relevance—An alteration in myofibrillar calcium sensitivity is not a basis for pathologic contracture development in muscles from RER-affected horses. Recurrent exertional rhabdomyolysis in Thoroughbreds may represent a novel heritable defect in the regulation of muscle excitation-contraction coupling or myoplasmic calcium concentration. (Am J Vet Res 2001;62:1647–1652)

Full access
in American Journal of Veterinary Research

Summary

After surgical removal of a primary intranasal neoplasm an implant device, designed to deliver 192iridium (192Ir) brachytherapy, was positioned in the nasal cavity of 8 dogs. Ribbons containing 192Ir seeds were placed in the device, using an afterloading technique. Dosimetry, to a dose of 7,000 to 10,000 centiGray (cGy), was calculated to encompass the site previously occupied by the tumor and a 1-cm margin of surrounding normal tissue. The quantity of 192Ir implanted varied between 16.69 and 100.80 mg of radium equivalent. The duration of implantation ranged from 90 to 168 hours. All dogs tolerated the implant well, but had a mucoid nasal discharge after radiotherapy. The implant device allowed rapid application and removal of the radioactive ribbons. Mean (± sd) radiation exposure to each radiotherapist during seed loading and unloading was 14.4 (± 5.3) and 4.5 (± 0.9) mrem, respectively. A uniform dose distribution around the intranasal implant device was achieved; however, dogs that received doses in excess of 9,400 cGy at the dorsolateral surface of the nose and/or hard palate had bone and soft tissue necrosis between 70 and 120 days after treatment. One dog was euthanatized 50 days after treatment because of metastatic disease, and 2 dogs were euthanatized because of local tumor recurrence at 125 and 212 days. Death, considered unrelated to treatment, occurred in 1 dog that was euthanatized 27 days after treatment and in 3 dogs that died 30, 93, and 456 days after treatment. Necropsy was performed on 3 of these dogs and evidence of intranasal neoplasia was not observed. One dog remained disease-free at 587 days after treatment.

Free access
in American Journal of Veterinary Research