Is your pony a ticking time bomb?

12:24pm Wednesday 14th March 2007

Laminitis has often been referred to as one of the cruelest afflictions horses and ponies can suffer.

The inflammation and pain in the sensitive laminae of the hooves has been compared to having 10 badly bruised fingernails then being asked to do a handstand on them!

Laminitis is a condition of the soft structures in the hooves: the laminae. Laminae are finger-like projections, which interlink to form a hammock. The "hammock" attaches to the inner surface of the hoof wall and slings the weight of the horse via the pedal bone. This is a terrible design fault because if the hammock should fail the pedal bone will drop and could even push through the sole of the foot.

Laminitis is a complicated physiological process but results in the laminae becoming inflamed or even dying off. Thus the "hammock" loses its strength and any movement (e.g. forced walking) can lead to catastrophic sinking and rotation of the pedal bone.

Laminitis is a veterinary emergency so don't delay and call your vet. In the meantime, if you can move the horse, transfer it to a deep bed (preferably shavings or sand) and do not move it further.

The classic laminitic stance

The signs and treatment for laminitis are multiple and generally well recognised by horse owners. I would like to draw your attention to a new concept called Equine Metabolic Syndrome and its links to laminitis.

Equine Metabolic Syndrome

Equine Metabolic Syndrome (EMS) explains exactly why obese horses and ponies are more prone to laminitis. Horses and ponies have evolved to use nutrients efficiently at times of scarcity (e.g. winter) and the over-feeding brought about by domestication often causes deposition of excessive fat stores.

It has been shown in the horse that certain fat cells (particularly those laid down in the crest and abdomen) are capable of affecting the action and manufacture of some important hormones and chemicals in the body. Not all fat horses necessarily have EMS. Just as the "apple-shape" in humans is more likely to lead to problems such as sugar diabetes and heart disease compared to the "pear shape", it's the type of fat cells and their location in the body that is important. The fat cells of the abdomen and crest are hormonally active leading to increased circulating cortisol and insulin resistance.

• Increased cortisol levels in the blood damages the laminae and also contributes to the development of insulin resistance. Increased cortisol is also a feature of Equine Cushing's Disease and hence EMS is sometimes referred to as Peripheral Cushing's Disease.

• Insulin resistance is the inability of the body tissues to react to the normal effects of the hormone insulin, released by the pancreas. Insulin normally causes certain body tissues to remove glucose from the blood and store it. If the body tissues do not respond to the actions of insulin, blood sugar remains permanently high (hyperglycaemia).

In addition, the body still recognises the high blood sugar and so more and more insulin is released- even though it is ineffective. This is similar to diabetes mellitus in humans.

• Insulin resistance and hyperglycaemia also causes damage to the laminae.

Diagnosis

In general, EMS horses are good-doers and owners find it hard to shift their excess weight. Fat deposition tends to be on the crest, behind the shoulders and rump. Some geldings develop swollen fatty sheaths. Quite often the ribs can be easily felt. Sometimes they have "sub-clinical" laminitis- i.e. evidence of changes in the hooves such as widening of the white line or divergent rings, without evidence of lameness.

Divergent rings on a laminitic foot

The new understanding of EMS has allowed us to develop a number of simple blood tests that will show if your horse or pony has underlying EMS and is therefore at increased risk of developing laminitis (even if he/she has not had laminitis before). The beauty of the test is that it is simple to obtain and allows us to predict a horse on the verge of laminitis and act accordingly to prevent the disease.

Treatment for EMS

A number of drugs have been trialled with varying degrees of success and this is an area of current interest for research. At present no wonder drug exists, so treatment of an EMS horse should be geared towards management and exercise:

Diet

• Maintenance requirements for a total forage-based diet is between 1.75-2.5 % of the horse's body weight., (e.g. a 500kg horse is likely to need 9kg of hay per day). Feed less than the horse's normal energy requirements to lose weight. Often this involves reducing the forage quality rather than the actual intake as horses do need a constant through-put of forage to ensure a healthy digestive system.

• Eliminate concentrates (if fed), giving hay of poorer nutritional quality (e.g. less leafy and more seedy/'stemmy') or making the horse work harder for the feed (double haylage net or pre-grazed fields).

• Remember to include a good vitamin and mineral supplement and/or protein feed balancer to make sure all essential nutrients are present in the diet. Do make sure the hay is of good hygienic quality despite its lesser nutritional value- mouldy hay is likely to cause respiratory disease.

• Avoid glycaemic foods with readily absorbable sugars e.g. carrots, apples, cereals, molasses, treats and fresh grass (particularly if grazed during the day).

• Feed hay soaked for 12 hours to remove soluble sugars, supplemented with low sugar chaffs.

Exercise

• This is an incredibly important part of the management of EMS. It has been shown that exercise increases the sensitivity of the body to the effects of insulin, therefore reducing the insulin resistance - pivotal in EMS.

• It also increases the body's energy demand and therefore aids weight loss.

• If it is impossible to ride the horse/pony, even lungeing or free-schooling for 30 mins twice daily is adequate.

• Remember, once the pony succumbs to laminitis it will be unable to exercise for at least four weeks after becoming sound without painkillers, and often recovery is much longer. In some cases, ex-laminitics are rarely sound again, so get into the exercise routine before it's too late!

If you would like more information about EMS and the tests involved, ask your veterinary surgeon. Charlie Briggs is available for your questions or comments at Garston Veterinary Group on (01373) 451115 or email cb@garstonvets.co.uk