Sometimes, I get a little concerned when research papers get picked up by the press. It's not necessarily because the research is weak, it's just that results sometimes get overstated or misinterpreted when they work their way outside of scientific forums.
A paper published in the latest edition of the American Journal of Veterinary Research is one of those. The paper (Tsuchiya et al. 2012) describes a study that looked at the impact of interferon-alpha (used to stimulate the immune system) and enrofloxacin (an antibiotic) on body temperature and lung fluid white blood cell counts in 32 horses that were shipped for approximately 26 hours in commercial vans. Horses either received just interferon or interferon and enrofloxacin before being shipped.
- After shipping, 3 antibiotic-treated and 9 untreated horses developed fevers. That's actually not statistically significant, by my calculations, and it's quite strange that the authors didn't do that analysis (and that the reviewers didn't pick that up).
- Two antibiotic-treated and 7 untreated horses were treated with antibiotics after arrival because of concerns about infections. Again, that's not statistically significant and it's surprising (and concerning) no one pointed that out.
- Overall, the average temperature of horses in the treatment group was significantly lower after arrival, but the clinical relevance of that is questionable since it was only a 0.4 C difference. Further, it's hard to say what a temperature immediately after arrival really means, since that's pretty early for a bacterial infection to have developed.
- There were significant differences in tracheobroncial fluid (fluid collected from the airways) between the groups, with lower white blood cell counts in the treated group. That's an interesting finding and is consistent with less inflammation. What that means in terms of disease prevention is harder to say, but it's something worth investigating further.
- There does not appear to have been any difference between the two groups in the ultimate health status of the horses.
This study provides some interesting information to help us think about how, when and why infections and inflammation develop after shipping. Results suggest that antibiotics might be useful in certain situations, but many questions remain. Any antibiotic use runs some risk of complications such as antibiotic-associated diarrhea. It also increases the risk of antibiotic resistance (and ultimately more problems trying to treat disease). We have to remember these issues when considering these results. Further, while it is typically much better to prevent disease than treat it, in situations like this, it's hard to say whether mass prophylactic treatment is actually preferable to early treatment, since horses can be observed closely after arrival and treated when early signs of disease develop. Ultimately, it's still not even clear from these data whether pre-treatment with antibiotics actually does have a positive clinical effect.
It's important to remember what this study tells us, and what it doesn't. Despite what some lay articles that have picked up the story say, it doesn't mean that antibiotics are broadly useful for keeping shipped horses healthy. The authors address this by stating "The use of enrofloxacin raises concerns regarding the emergence of antimicrobial-resistant bacteria, and it is important that antimicrobials such as enrofloxacin are not used inappropriately. The guidelines for enrofloxacin use in the Japan Racing Association’s medical office require that it is only administered as prophylaxis against transportation-associated fever when the duration of transportation is expected to be ≥ 20 hours and the horse has had clinical signs of transportation-associated fever before or is considered to be at risk for developing transportation-associated fever (eg, if the horse has undergone laryngoplasty or has a history of pneumonia)."
Regarding the big picture, however, this should make us think again about how we manage horses. Antibiotics should never be used as a crutch in place of good management. In a situation like this, where 19% of horses treated with interferon and enrofloxacin and 56% of horses treated with interferon alone get sick, something's wrong. Antibiotics may be an easy way to try to reduce the likelihood of disease in some situations, but that doesn't mean it's a good idea. Considering the number of horses that get sick (and die) every year from shipping-associated illness, maybe we need to rethink how they are transported. Is lack of antibiotics the problem, or is it how (and how long) horses are shipped? Maybe long, interrupted trips aren't a good idea, antibiotics or not.