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Objective—To evaluate the effectiveness of a novel trimethoprim-sulfadiazine oral suspension for the treatment of naturally acquired Streptococcus equi subsp zooepidemicus infection in horses.

Design—Randomized, controlled field trial.

Animals—180 horses with S equi subsp zooepidemicus infection.

Procedures—Horses with lower respiratory tract infections caused by S equi subsp zooepidemicus were treated with a new formulation of combined trimethoprim-sulfadiazine oral suspension at a dosage of 24 mg/kg (10.9 mg/lb) twice daily for 10 days (treatment group) or with an equivalent volume of saline (0.9% NaCl) solution (placebo group). Response to treatment, including clinical signs and fecal consistency scores, was assessed twice daily. Any adverse effects were recorded. The primary outcome variable was clinical response; the secondary outcome variable was eradication of S equi subsp zooepidemicus on study day 17 as determined by bacteriologic culture of repeated transtracheal-wash specimens.

Results—Of the 119 horses allocated to the treatment group, 69 (58%) had a positive clinical response. A significantly smaller proportion of horses in the placebo group (9/61 [15%]) had a positive clinical response. By day 5, 25 of 61 (41%) placebo horses had been withdrawn from the study because of negative clinical response, compared with only 10 of 119 (8.4%) treated horses. By day 10, 28 of 61 (46%) placebo horses had been withdrawn because of negative clinical response, compared with only 13 of 119 (11%) treated horses. There were few adverse events associated with the trimethoprim-sulfadiazine suspension. There were no significant differences in fecal consistency scores between treatment and placebo groups.

Conclusions and Clinical Relevance—The new oral suspension administered at 24 mg/kg twice daily effectively treated the clinical signs of S equi subsp zooepidemicus lower respiratory infection in horses and eliminated the organism from the respiratory tract. Adverse effects were minimal.

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in Journal of the American Veterinary Medical Association


Case Description—A sudden onset of extreme dysgalactia in gilts and sows in a 1,000-head farrow-to-wean herd was observed in December 2009. Signs of dysgalactia were identified in sows beginning 1 day after parturition and lasted 4 to 6 days. This resulted in a mean piglet preweaning mortality rate of 18% because of starvation.

Clinical Findings—Sows were neither off feed nor febrile. Udders were not inflamed or congested. Feed sample analysis did not find ergotamine, mycotoxin contamination, or ration formulation errors. Management practices were acceptable. Piglets attempted to stimulate milk production but none was elicited. Oxytocin (20 U) caused milk ejection but the effect was short-lived. Blood samples from sows with affected litters were positive for Mycoplasma suis (formerly Eperythrozoon suis) by PCR assay, and blood samples from sows with unaffected litters were negative.

Treatment and Outcome—Chlortetracycline fed to the entire sow herd at 22 mg/kg/d (10 mg/lb/d) for 2 weeks resulted in a near complete absence of dysgalactia in sows farrowing within 5 weeks after the start of treatment. Dysgalactia did occur in sows that received chlortetracycline > 5 weeks prior to farrowing. Currently, gestating sows and gilts receive chlortetracycline in feed at a dosage of 22 mg/kg/d for 2 weeks beginning 3 weeks prior to farrowing.

Conclusions and Clinical RelevanceM suis is spread primarily by blood contact from animal to animal, and diagnosis of infection with this organism can be easily missed by means of standard diagnostic protocols unless PCR assays or specific stains are used. Therefore, its current prevalence and impact are likely to be greatly underestimated.

Full access
in Journal of the American Veterinary Medical Association