Dietary strategies to overcome compromised eating and chewing functions

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Dr Derek Cuddeford, Royal (Dick) School of Veterinary Studies, University of Edinburgh

The only true wild horses are the Tarpan and Przewalski, the remaining non-domesticated animals are feral horses, principally the Mustangs in North America and the Brumbys in Australia. Other examples of feral horses are the Banker Horses on the outer banks of North Carolina, the Chincoteague Ponies on the Assateague Islands off the coast of Virginia, the Misaki horse of Japan and the Welsh ponies found in the Carneddau Hills of North Wales. There are also semi-feral herds including the Konik, Camargue, Connemara and our own Exmoor, Dartmoor and New Forest ponies. The survival of these animals is threatened by mountain lions, wolf packs, man and vehicles among other things depending on their respective location but most importantly by compromised eating and chewing functions. All herbivores are reliant on maintaining the functionality of their teeth for survival be they a Zebra or a Scottish Blackface Sheep. It is impossible to overstate the importance of teeth and chewing to a herbivore’s survival. Loss of teeth equals loss of condition and ultimately death.
Our horses are under our control so we have the opportunity and responsibility to compensate any deficiencies in the eating process. This is composed of two parts, harvesting/ingesting food and then, processing it. The lips of the horse are wonderfully mobile particularly the top lip. If you feed your horse a coarse mix it is quite educational to then watch it and observe how it uses its top lip to sort out the ingredients. It flicks the mixture back and fro in order to find those particles that it likes most. In contrast, cows have a fairly immobile top lip although others such as sheep and giraffes have quite mobile lips allowing food selection. When grazing, a cow just grabs some grass and pulls being fairly non-selective whereas a horse sorts out what grass it wants to consume before grasping it with its incisor teeth and biting it off. This requires that the upper and lower incisors are in direct apposition. Parrot-mouthed horses or those with undershot lower jaws are unable to grasp or prehend their food easily and will thus starve to death in extreme conditions unless something is done. Thus, it is unrealistic to expect these animals to do well in a foraging situation such as at grass depending of course on the extent of the malformation. Providing chopped forage to these animals is the best way of ensuring they get enough fibrous feed. Normally they can ingest concentrate feed using tongue and lips but if they have difficulty, then moistening the feed facilitates intake. Loss of some incisors can reduce the efficacy of the animal’s harvesting ability so it is necessary to keep a close watch on body condition when such animals are kept at grass/fed hay. When sheep begin to lose their incisors at about 5/6 years of age (they only have a bottom row and a dental pad upstairs) they are doomed. In 1980 an Edinburgh dentist created false incisor teeth for sheep in order to lengthen their productive life but the project never became a commercial reality. As yet no one has attempted the same for horses in terms of making regular false teeth although some acrylic structures have been produced.
The horse’s lower jaw is narrower than the upper jaw so incomplete lateral movement results in uneven wear which is manifest by the formation of sharp enamel points. These form on the inside of the teeth of the lower jaw causing lacerations to the tongue and on the outside of the upper teeth resulting in damage to the interior of the cheek. If not recognised at an early stage the problem will become apparent when the horse starts to drop food from its mouth whilst eating (quidding). This problem is easily rectified by rasping (sometimes known as “floating”) the teeth so that the molar occlusal surfaces are all in contact. Hooks and shear mouth are other problems encountered in the horse population which can be solved by your veterinarian applying the appropriate dental techniques. Thus, there are various oral problems that can be overcome by dentistry alone once realised and no special dietary strategies are required.

 
In contrast to the above, the permanent loss of teeth and an impaired occlusal surface (the premolar and molar teeth generally known as the “molar battery”) require that special diets are used to avoid the animal fading away simply because it either cannot harvest food effectively or, it cannot process it properly. Dietary ingredients that are to be used in pelleted diets are ground to form a grist which then goes through a pelleting machine that uses steam, molasses or other binders to stick everything together. Because of this processing, pelleted diets are ideal for horses with a seriously compromised chewing apparatus. To make things even easier for the horse, water can be added to the pellets so that they disintegrate and can then be “hoovered” up. A coarse mix might be alright for a horse whose molar battery is not too badly compromised. It is a question of monitoring condition and observing the faeces for evidence of unprocessed dietary ingredients such as long fibre particles or whole grains in order to make sure that your feeding strategy for the horse is the correct one.
Many horses with compromised eating and chewing function do not need concentrate in whatever format because they are not in work. For these animals it is necessary to feed forage, the precise format depending on the extent of the problem and the forage quality required. As mentioned above prehension problems can be overcome using chopped forages but this might not work if there are significant food processing issues. Certain forages are available in a ground and pelleted form such as dried grass pellets or dried lucerne pellets; both high quality feeds. These forage pellets can be soaked in the same way as concentrate pellets and are suitable for horses that have very poor grinding capacity. In less severe cases it may be possible to feed low dry matter haylages in which the material has fermented and it is quite soft. This will be much easier to process than dry mature grass hay which can sometimes be more like straw. Fortunately, nowadays commercial feed manufacturers produce fibre cubes that have nutrients added to the processed fibre so they can represent a complete “package” for your horse. Depending on which product you use you will find the appropriate feeding advice on the bag or internet. These products can be fed dry or soaked to produce a mash which the horse can easily consume.
In conclusion, the domestically kept horse can be kept alive for a very long time even if its oral functionality is seriously compromised. Thus we have many horses living for up to 40 years now when otherwise in a natural environment they would have long ceased to exist. We must be grateful for the availability of modern manufactured feeds that allow us to keep our “seniors” going.

Author: The Editor

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