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We take it for granted that when our horses suffer from a bacterial infection there is a straightforward way to treat it — with antibiotics.

But new research has shown the time has come to stop being complacent. A fresh threat has arrived — antibiotic resistance following a stay in equine hospital.

Why the cause for concern?

Bacterial populations are smart. Ever since penicillin was first developed in the 1940s, they have been evolving ways to resist the attacks they receive from antibiotic treatment.

Whenever new antibiotics are developed, bacteria are susceptible to their actions to begin with but, within a few months, more of them will start to develop resistance until, eventually, the medication will be of little value.

A recent experiment conducted by Adele Williams and her team of researchers at the University of Liverpool showed why we should be taking this issue seriously.

The study proved that while kept in a home environment horses are at a relatively low risk of meeting bacteria that are resistant to antibiotics — problems start when they are hospitalised with other horses.

The effects of hospitalisation

Funded by The Horse Trust, Adele Williams’ project aimed to highlight the problem of antibiotic resistance and the effect hospitalisation of horses has on this.

Samples of droppings from horses arriving at an equine hospital were tested for the gut-borne bacteria E.coli. The same horses were tested again seven days later.

E.coli was chosen because it is present in the gut of all horses and it has the potential to cause infections in certain instances, for example in wounds. Recording how many of these bacteria were resistant to antibiotics gave a measure of the amount of bacteria associated with the horse that could be resistant to treatment at any one time.

The results of the study were conclusive: they showed that while the levels of resistance in horses admitted to the hospital were low, after seven days of hospitalisation, the levels of bacteria resistant to seven of eight common antibiotics used to treat horses increased significantly.

Furthermore, this increase occurred in every horse, no matter whether they were treated with antibiotics. It was the fact they were hospitalised that was important.

Interestingly, one of the common antibiotics used in equine veterinary practice, trimethoprim-sulpha — the most commonly prescribed antibiotic as it can be given easily in the horse feed — showed a high level of resistance in both horses when entering the hospital and also after seven days of hospitalisation.

Nearly one in three horses that were admitted to the clinic carried bacteria that were resistant to trimethoprim-sulpha, but this increased to two out of three horses after they had been in an equine hospital for a week.

For the full article on antibiotic resistance, see the current issue of Horse & Hound (18 February, ’10)

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