Equine veterinary discoveries: intellect, hearing and eyes including one cure *H&H VIP*

Peter Green MRCVS presents the latest scientific research — from inherited intelligence to problems with eyes and ears

Brainy at birth

Behavioural scientists in Pennsylvania have shown conclusively that the speed and ability to learn from new experiences is firmly linked to a pony’s parentage.

They took more than 100 semi-feral native ponies from a large herd and measured how long it took them to learn that touching a flat, plastic fly swatter with the muzzle resulted in a food reward. The youngsters were all unhandled, except for basic halter training.

Some ponies took a long time to make the connection, while others picked it up really quickly.

The scientists then analysed their breeding and found a strong correlation with both sire and dam lines. This shows that learning ability is significantly inherited. If the pony’s parents were bright and clever, he was likely to show such traits too.

Such results indicate that selection for temperament and learning played an important part in the domestication of horses — and continues to have a significant role in the way in which closed breeds develop over succeeding generations.

Is he deaf?

The hyoid bones make up a bony “hammock” slung from underneath the skull, supporting the larynx in the throat (diagram, top). When a horse swallows and as he breathes deeply at exercise, the suspended larynx swings backwards and forwards.

Unfortunately, in some horses — and especially in ponies — the joint between the hyoid bones and the base of the skull can become arthritic, a condition called temporohyoid osteoarthropathy (THO).

This gives rise to a variety of clinical signs: some horses headshake and some have difficulty eating, while others resent the bit and cannot adopt a correct head position when ridden. In severe cases where the joints fuse together, forced poll flexion can cause fractures of the affected bones.

The site of the arthritis is complicated, with lots of blood vessels, nerves and lymphatics all squashed into a small space. No wonder that some horses with THO show nerve signs such as facial paralysis.

Treatment can involve painkillers and even surgery to cut out affected joints. Some cases respond very well, regaining function and flexibility.

But vets in California have just published work highlighting another side effect of THO. Using the latest neurological instruments they showed that most animals with THO become deaf. Cases that had apparently “recovered” after treatment were still deaf, with no prospect of regaining hearing.

Owners of recovered patients must be told that their horses will be unaware of loud noises, such as approaching traffic, or respond to voice commands.

A cure for runny eyes

Many horses suffer from perpetual runny eyes.

In summer this can be made worse by flies, which introduce infection and make the eye secretions more sticky and gummy.

The tears that lubricate the eyes should drain down the nasolacrimal duct, which runs from the lower corner of the eyelids down through the skull to the nasal chamber. When open and clear, this tube functions well and there is no overspill from the eye.

If it is blocked, however, tear spillage and secondary infection are common.

The duct is long with some sharp bends where blockages can easily occur. Vets frequently have to flush out the ducts with sterile solution to try to re-establish proper drainage, but this often provides only temporary relief and the procedure needs doing repeatedly.

Vets in Sweden and the US have just reported a new and simple surgical operation that offers a permanent cure. They have developed a technique to dilate the first part of the duct, before passing a sterile synthetic tube through this dilated portion and the thin bone between the eye socket and the maxillary sinus.

The tube is left in place for six weeks and then removed. The diverted nasolacrimal duct must no longer transport tears all the way down to the nose, but can drain directly into the sinus.

Ref: Horse & Hound; 3 March 2016