The well-known phrase “eating like a horse” does not always ring true. Sometimes, horses have trouble eating. This is a condition called dysphagia, which literally means “difficulty in swallowing”, but it is commonly used to describe a general difficulty in eating.
There are many reasons why a horse could have dysphagia. There may be a physical problem with getting food into the mouth – for example, instability of the mandible or jaw. Sometimes horses snag their lower jaw in a stable door catch, panic and then pull back, resulting in a fracture of the lower jaw – a readily apparent reason for dysphagia.
A systemic disease such as botulism can also result in poor eating. For example, ingestion of the botulinum toxin affects the conduction of impulses along the nerves and causes dysphagia. But it is not only the nerves involved in swallowing that are affected, so that other signs such as generalised weakness may be present.
The process of eating can be broken down into several steps. The initial stage is getting the food into the mouth. It then has to be chewed or masticated, swallowed and passed on to the stomach. Problems can be encountered at any of these stages. In equine practice, the most common problem is choke, which occurs when a soft ball of chewed food (a bolus) gets stuck in the oesophagus and fails to pass into the stomach.
If we consider each stage of eating separately, we can understand how problems arise in this everyday but complex, carefully co-ordinated activity. These are as follows:
The upper and lower lips are the main structures involved in grasping food, aided, to a lesser degree by the incisor teeth and the tongue. Horses are usually very careful and particular about what objects they take into their mouth when grazing: it is surprising how the horse’s relatively large, clumsy-looking lips can pick up individual pony nuts from the ground. It is obvious how wounds to the lips or tongue, fractures of the upper or lower jaw and neurological diseases affecting the nerves of the lips, will cause difficulty in getting food into the mouth.
Problems in this stage are usually caused by dental disease – for example, fractures of the teeth, gum disease, damage to the soft tissues of the mouth, occasionally, tumours in the mouth or, rarely, damage to the temporomandibular (ie jaw) joints.
This is a very complicated procedure. One of the first signs of a problem is the return of saliva and chewed up food from the nostrils as well as coughing, due to food being aspirated into the lungs.
Difficulty swallowing may be caused by congenital (present at birth) or acquired problems. The former includes cleft palate and developmental problems of the structure of the larynx (voice-box) or pharynx. Animals with these deformities will have problems from early life, so the age of the horse when the problem was first noticed may give a useful clue as to the possible cause.
Acquired causes include “space occupying lesions” of the pharynx, for example polyps, abscesses, neoplasia or foreign bodies. Sometimes, swellings on the head which exert external pressure on the pharynx, such as snakebites or a strangles abscess, can cause a problem with swallowing, but the first sign with these lesions is usually a marked respiratory noise.
Diseases affecting the nerves that co-ordinate swallowing, such as grass-sickness or a fungal infection in the guttural pouch – also have a role to play.
Choke is a common problem which occurs when an accumulation of food material blocks the oesophagus. Classical, unsoaked sugar beet is a cause, but choke can also occur with cubes, grain and any poorly chewed fibrous material, especially when the food is bolted down very quickly.
Dysphagia can be present from birth or occur suddenly. Whatever the case, it is important to consider all the possible causes and conduct a thorough veterinary examination. The sooner a diagnosis is made, the sooner treatment can begin, and the sooner your equine can be eating like a horse once again.