Antibiotic Use and Abuse: Example of Equine Asthma

The number of infections resistant to antimicrobial medications, or antibiotics, rises every year, as do patient deaths due to untreatable infections. Using antibiotics inappropriately contributes to antimicrobial resistance in both human and veterinary medicine. Because of this, a push is afoot globally to minimize and optimize the use of antimicrobials in both sectors.

“Antimicrobial stewardship is important in equine practice; however, inappropriate use of antimicrobials has been reported,” noted Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor.

A group of researchers interested in improving antimicrobial stewardship created and distributed a global online survey to equine veterinarians.^* The survey presented three different cases, each describing a horse with varying forms of equine asthma (i.e., severe, moderate, and mild). Veterinarians were asked if they would prescribe an antibiotic using a five-point verbal rating scale from 0 (never) to 4 (always) based on the details provided in the scenarios.

“Considered a noninfectious respiratory disease, equine asthma is characterized by airway inflammation and hypersensitivity. Common clinical signs include coughing, wheezing, and nasal discharge but no fever,” described Whitehouse.

Results of this survey showed that over half of the 249 survey respondents (53%) indicated they would use antimicrobials “at least sometimes” in one or more of the three presented asthma cases.

“That said, respondents that would ‘never’ use antimicrobials ranged from 63-70% depending on the case scenario,” Whitehouse said.

The most common reason cited by survey participants for selecting an antimicrobial was a suspected secondary bacterial infection. Trimethoprim sulfonamide combinations were most frequently prescribed (80% of antimicrobial-using respondents); however, drugs considered “critically important antimicrobials,” including the cephalosporins and fluoroquinolones that should be reserved for human medicine, were prescribed by a few veterinarians (7-11%).

Included in the survey was a knowledge test regarding the pathophysiology of equine asthma—i.e., how the disease develops. Practitioners who scored higher on the knowledge test used fewer antimicrobials in the mock cases. Survey respondents who worked in primary practice used antimicrobials more often than veterinarians working in academic hospitals or private referral hospitals.

Practitioners identified several factors that influenced whether they prescribed antibiotics. The most common factors included the results of a transtracheal wash culture, response to other forms of therapy, and whether stablemates had similar clinical signs.

“According to the research team, this is the first report of antimicrobial prescription behavior with a focus on asthmatic horses. Several areas to promote antimicrobial stewardship in equine practice were identified, including educational intervention and clear worldwide guidelines and regulations on antimicrobial use,” shared Whitehouse.

In summary, the researchers found a high number of veterinarians prescribed antimicrobials for equine asthma, even though bacterial infection is not considered a primary cause. Critically important antimicrobials were used by a small proportion of respondents. Veterinarians having an improved understanding of the development and progression of asthma prescribed antimicrobials less often.

“Allergen avoidance is a key management strategy for horses with equine asthma, and the respirable dust, endotoxins, and other antigens found in hay and bedding are important asthma triggers,” said Whitehouse.

One way of managing asthmatic horses is hay soaking or steaming to reduce the respirable load of the hay compared to dry hay.

“A recent study also reported benefits when feeding haylage compared to dry hay in reducing dust exposure,” Whitehouse shared.

In addition to minimizing dust exposure, asthmatic horses may benefit from receiving supplementation with long-chain omega-3 fatty acids to support a strong immune system. Look for a direct source of DHA and EPA, two omega-3s with the highest biological activity, such as EO-3.

^*Van den Brom-Spierenburg, A.J., A.N. Mureșan, and C.M. Westermann. 2024. Antimicrobial prescription behavior in equine asthma cases: An international survey. Animals (Basel) 14(3):457.