Hoof Conditions and Problems Within the Hoof Capsule

10 Hoof Conditions and Problems Within the Hoof Capsule


10.1 Hoof Balance


To assess hoof balance, each foot needs to be examined from several different perspectives. First of all, looking from a lateral view the hoof pastern axis can be evaluated. The angle of the dorsal wall of the hoof should be the same as the angle of the first and second phalanges. If the dorsal wall has too low an angle the axis is said to be broken back; the reverse, when the dorsal wall is too steep, is said to be broken forward. This condition is so commonly seen in donkeys that it may even be considered to be normal. The coronary band should be examined from the lateral aspect; it should form a very gradual downward slope from the dorsal point to the bulb of the heel. Secondly, the foot should be examined from behind; the distance from the coronary band to the ground should be equal between the lateral and bulbs of the heel. Thirdly the foot should be examined from the front; a line through the foreleg should bisect the hoof and the coronary band should be parallel to the ground. Lastly, the bottom of the foot is examined; the weight-bearing surface should be symmetrical and the sole slightly concave. Practitioners should note that as many as 25% of horses will not have symmetrical feet, comparing left and right. This is not an unsoundness as such but should always be noted. Figure 10.1 demonstrates poor hoof balance.


10.2 Puncture Wounds of the Foot


These may be trivial but should never be treated in a cavalier fashion, for if deep tissues are involved these wounds can be life threatening (see Fig. 10.2). Clinicians need to be careful what they say; it is all too easy to let the owner think that the farrier is to blame, but it can be very difficult for the farrier if there is little hoof wall in which to place nails well clear of sensitive tissues. If the nails are too close to the sensitive tissue but not penetrating it the result is ‘nail bind’; the horse will show mild lameness within a few hours of shoeing and there will be pain around the offending nail when hoof testers are applied. The offending nail should be removed. Normally, the condition will settle down with a relatively low dose of NSAIDs. Clinicians must remember to determine the tetanus immunity status of the horse.


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Fig. 10.1. Poor hoof balance.


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Fig. 10.2. Careful examination of the foot.


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Fig. 10.3. Pus being drained from the foot with a hoof knife.


If there has actually been a shoeing prick there will be immediate pain, and there may be haemorrhage. If this occurs actual sepsis is less likely to occur but, if it does occur, the degree of lameness will get worse over 48 h until in many cases the horse appears to be fracture lame. The shoe should be removed and the foot poulticed. If possible the point where the sepsis has built up should be cut open carefully with a hoof knife to allow the pus to be released (see Fig. 10.3). Timing may be difficult, as from a welfare point of view the clinician wants to open the hoof as soon as possible. However, it is difficult to visualize the purulent tract if the approach is made too early. Obviously, NSAIDs will be helpful in this situation. The horse must be covered for tetanus. Pressure may be put on to the clinician by the owner to administer antibiotics, but these are rarely helpful unless the infection has spread up the leg, resulting in a painful swelling. This is not the case in the donkey, where an i/m injection of procaine penicillin is helpful.


The third problem associated with shoeing is when the shoe is too short, so that the end or ends of the shoe lie not on the wall but on the sole. A corn develops in the angle between the wall and the bars of the foot; this position is called the ‘seat of corn’. Lameness may be mild unless there is actual sepsis, and then it will be pronounced. Treatment for an infected corn is similar to that for a foot abscess, as described following shoe prick. It should be remembered that drainage is vital. Corns do not occur in the unshod horse.


Most abscesses in the foot are not related to shoeing, and in fact are more common in the unshod horse. The initial penetration often goes unrecorded, or the infection may be from haematogenous spread. Pus builds up between either the wall or the sole of the hard hoof and the underlying soft tissue. The pain is intense and is relieved only by releasing it with a hoof knife or by the pus breaking out above the coronary band. A classic history of an untreated horse would be lameness progressing in severity over 72 h and then suddenly improving. If the point where the pus is escaping can be found then the point of penetration will be directly below it. Ideally, a hole should be made in the sole. Sterile saline can then be irrigated into one hole and will flow out of the other. Both holes should be kept open to allow the soft tissue to heal within. If pus is allowed to build up again pain will return and the degree of lameness will increase. Therefore, it is advisable that a poultice is applied until healing is completed. The horse can be shod when the infection has dried up. NSAIDs can be given to reduce the pain. Once again, the horse must be protected against tetanus.


Clinicians should always be on their guard to detect serious foot penetrations. These may cause articular sepsis of the navicular bursa, the distal interphalangeal joint or involve the deep digital flexor tendon sheath. If the penetration is in the frog or the sulci the path of the penetration will be very difficult to follow. The whole foot will be very painful so hoof testers are not very helpful. Because of the pain strong sedation will be required, or even an abaxial sesamoid block. In the chronic situation it is important to debride all the affected tissue and then poultice the foot to allow continual drainage. This will occur for several weeks if there has been damage to the pedal bone. If there has been synovial penetration radical debridement is required. This can be performed with a general anaesthetic and an arthroscope. However, in field conditions a cure can be effected eventually by radical drainage. This operation is called a ‘street nail’ procedure. Welfare here is very important; high doses of NSAIDs will be necessary.


10.3 Thrush


Thrush is a degenerative condition of the horn of the sole and frog caused by anaerobic bacteria. It is made worse by poor hygiene, i.e. the horse continually standing in faeces and urine. None the less, thrush is not caused by bad conditions alone and so the practitioner should not be too quick to blame the owner. The condition will be recognized by the smell and the black, crumbling horn tissue. Rarely does the condition cause lameness unless the sensitive tissue is involved. If there is tracking of pus up in the middle of the frog, pain may be found in this area under digital pressure, and the horse will be seen to be lame when trotted up. Radical removal of the abnormal horn tissue is required. Hydrogen peroxide, as a cleansing agent, is useful on account of the anaerobic bacteria present. Formalin, vinegar, zinc and copper sulfate have all been used for treatment in this condition. It should be remembered that in all foot pain it is unlikely that the degree of lameness will be altered by flexion tests.


10.4 Keratoma


A benign but locally invasive tumour, keratoma is rare. Its initial manifestation will be seen as ‘pus in the foot’. The observant clinician will notice the white disc of abnormal horn. Once the pressure of the pus has been relieved the lameness will stop, although it will soon recur. Radical treatment is required to remove the wall of the hoof lying over the fat, worm-shaped tumour running up towards the coronary band. This has to be removed in total or recurrence will occur. The hole in the hoof must be packed with gauze soaked in iodine. The hole regenerates very quickly. The condition following radical removal carries a good prognosis.


10.5 Laminitis in the Horse and Pony


Laminitis is extremely complex, not only in its aetiology but also in its pathology. The classic cause in horses – and more commonly in ponies – is too much rich, green grass. Grass that is itself under stress, i.e. when the nights are cold but the days are hot, is more likely to bring on an attack of laminitis. There will be a higher level of fructans in the grass. Animals become overweight, with a rock-hard crest of fat and suddenly become acutely lame. This can occur in all four legs, but much more commonly in only the front legs. The animal will adopt a classical laminitic stance, leaning backwards and trying to take as much weight on its hind legs as possible. It will be very reluctant to move. However, if it is on soft ground it will move better once it has got started. This accounts for the old-fashioned treatment which was to make the animal work. This should not be done, however, as it is not only cruel but also it bruises the feet and makes the condition worse. Having stated this if the owner thinks that the pony or horse is about to get laminitis then exercise on soft ground is beneficial; animals being worked consistently rarely get laminitis. If a case is suspected the animal should immediately be taken away from any access to grass. In severe cases of laminitis the animal may well lie down; this is good and should be encouraged.


Diagnosis should not be a problem, though inexperienced clinicians must beware of mistaking the recumbent laminitic with the recumbent colic. Animals with laminitis will continue to eat but obviously, apart from a measured quantity of good-quality hay, that should be discouraged. The animal with laminitis will have marked bounding digital pulses, whether felt in the palmar digital position or in the abaxial sesamoid position. The laminitic will be reluctant to have a front foot picked up, as this puts a higher load on the already painful opposite front foot. If the clinician is able to hold a front foot up it will be found that the foot in the area of the sole halfway between the toe and the point of the frog will be extremely sore on hoof testing. In very severe cases of laminitis the sole of the hoof will be painful even simply on thumb pressure.


Sadly, in neglected cases clinicians will observe that the pedal bone has penetrated the sole. In these cases prompt euthanasia is advised. In other cases, particularly in heavy horses or cob types, the pedal bone will sink within the hoof capsule. This can be perceived by pushing a finger into the groove that will have appeared at the coronary band: this action will be acutely painful for the horse.


Acute laminitic cases should be treated as an emergency. As stated above, the diet must immediately be adjusted to avoid hard food and grass. The surface on which the animal is standing is also very important. Sand or a very deep bed of shavings are both recommended; straw is less suitable, since not only will the horse eat it and may then get an impaction, but also the straw may be scraped round by the horse until it is then standing on bare concrete. Deep manure might be considered, but it should be avoided as it tends to soften the feet excessively and may bring on other conditions (see thrush, above). Concrete or very compact earth are the worst possible surfaces: these should be covered with rubber matting. If this is not possible the feet should be covered with a clog of thick polystyrene. Another action which might be suggested is to apply ‘lily pads’, which are pieces of hard rubber approximately the same size as the frog. They should be taped on to the frog with gutter tape to apply ‘frog pressure’.


There is still an ongoing debate on what to do about shoes. One school of thought suggests that you leave the shoes in place, as they are at least providing some support. It is certain that removing shoes will be very painful for an acute laminitic. It is also certain that it will be impossible to replace the shoes. Another school of thought suggests you remove the shoes so that the animal can be more comfortable taking weight on its soles rather than on the walls of the feet. When the animal has become more stabilized, heart bar shoes may be fitted to apply frog pressure. These may be either solid-fixed heart bar shoes or more sophisticated adjustable shoes, the latter being capable of having more pressure applied by being tightened up twice a week. There are also modern malleable materials which can be fashioned to the shape of the hoof to give the horse more comfort. Obviously, once the initial acute pain is controlled, the feet will need to be trimmed by a skilled farrier. The toes should be radically shortened to try to make the angle of the hoof conform to the angle of the pedal bone. A skilled farrier will probably be able to do this by eye. However, a lateral radiograph will be very helpful here.


Apart from these husbandry aspects the main treatment is focused on providing pain relief and reducing the inflammation; NSAIDs will play a very pivotal role, the most commonly used being phenybutazone, but others described in Section 5.8 all have their followers. Clinicians should pay strict attention to the weight of the animal and dose accordingly. They should remember that with the husbandry advised above, the weight should be reducing rapidly, and doses thus must be reduced accordingly. Clinicians must remember that the dose rate of phenylbutazone for the donkey is twice that for the horse.


The other treatment aspect which may be considered is lowering the blood pressure by the use of acetylpromazine (see Section 7.1). This medicine is also a tranquillizer, and will have the added benefit that it will help encourage the animal to lie down. Owners should be told of this other effect so that they are not concerned if the animal appears sedated. Obviously, this medicine should only be used for a limited length of time, i.e. for a maximum of 3 days.


Laminitis is not only caused by overfeeding of green grass, it can also be caused by overfeeding of concentrates. The classic example is the horse which has broken into the feed shed and gorged itself overnight. The first task in treatment is to try to move the ingesta rapidly through the intestine to cut down adsorption. This can be achieved by giving magnesium sulfate (Epsom salts; 0.5 kg for a 500 kg horse) dissolved in water, by naso-gastric tube. Sodium bicarbonate can be added to this to act as an antacid, as well as bismuth and charcoal to act as adsorbents for the toxaemia. It is not only the excess carbohydrate that will cause the laminitis but also the toxaemia. The NSAID flunixin meglumate should be injected i/v to help counteract the endotoxaemia.


Toxins from other sources will also cause laminitis. Metritis from a retained fetal membrane, if not treated aggressively, will cause a toxaemia and laminitis. Equally, a mastitis if not treated with antibiotics and NSAIDs will cause a toxic laminitis. Any poison that causes a toxaemia may result in laminitis, e.g. acorn poisoning causing an impaction may well cause a bowel toxaemia by delaying ingesta transport time.


Severe pedal concussion, e.g. a pony galloping several miles on a tarmac road, will result in laminitis in all four feet. A horse with a fracture, if not fully supported by slings, may well develop laminitis in the opposite leg to the fracture on account of the excess weight load on that foot.


All these causes must obviously be avoided. However, in the event of laminitis the condition should be treated in a similar way as described above.


One other cause of laminitis is high levels of circulating corticosteroids. This may occur in Cushing’s disease (see Fig. 10.4), as described in Section 19.16, or it may occur iatrogenically by veterinarians injecting corticosteroids. These injections, e.g. for joint medication, should be limited to a very few at any one time. Steroids should not be injected to treat conditions such as urticaria in the overweight animal, which is a likely candidate for developing laminitis.


10.6 Laminitis in the Donkey


Donkeys, like horses, may become laminitic for a variety of reasons, but the most common are either too much lush grass or grain overload. Donkeys will also suffer laminitis as a result of Cushing’s disease. It is very important that donkeys are not starved, as this may result in hyperlipaemia, which should be avoided at all costs.


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Jun 11, 2017 | Posted by in GENERAL | Comments Off on Hoof Conditions and Problems Within the Hoof Capsule

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