A Silent Killer – Cushing’s Disease

We all know that the cause of laminitis in the vast majority of cases is an underlying hormonal problem in the endocrine system. The two endocrine problems that leave a horse susceptible to laminitis are equine metabolic syndrome and Cushing’s disease. But which would you associate with Cushing’s disease – the elderly pony with the thick curly coat, or the international grand prix dressage horse in full training?

Australian dressage rider Brett Parbery knows to his cost that Cushing’s is not restricted to the equine OAP – he lost his Olympic hopeful Victory Salute to the disease in late 2011. He was only made aware of the presence of Cushing’s once the warm blood gelding developed severe and incurable laminitis. With recent research indicating the Cushing’s victory salutedisease can affect much younger horses than previously though, it’s important to be aware of its deadly potential and how it can affect your horse.

Cushing’s; what is it?

Cushing’s disease is called by the abnormal function of the pars intermedia part of the pituitary gland, which is situated at the base of the horse’s brain. The disease’s acronym – PPID – stands for pituitary pars intermedia dysfunction. In healthy horses, this part of the pituitary gland is under tight control. A horse’s age, however, this control starts to fail, so the gland enlarges and produces abnormal levels of several hormones in the blood stream.

Laminitis is one of the most devastating clinical signs of the disease and has significant consequences for the welfare of the affected horse or pony. Other PPID symptoms include excessive hair growth or abnormal hair growth patterns, such as a delayed shedding of the winter coat, and fatty tissue redistribution throughout the body. You should look out too for increased thirst and urination along with lethargy, sweating and a greater susceptibility to infection.

Exactly how PPID causes laminitis has yet to be clearly established, although researchers have demonstrated that high blood levels of insulin will cause laminitis in horses and ponies. Studies at Liphook Equine Hospital laboratory this year identified that PPID cases often have disproportionately high blood insulin levels in response to eating feeds containing glucose, when compared with healthy horses. It is suspected that high levels of insulin also occur when these horses graze pasture – which leads to an increased risk of laminitis.

A geriatric disease?

cushing's'When a horse shows some of the typical PPID symptoms, a vet may be able to make a presumptive diagnosis simply by discussing the horse’s history and performing a clinical examination. It is suspected, however, that PPID may result in laminitis well before other clinical signs are apparent. An additional blood test is often used to reach a definite diagnosis.

Adrenocorticotrophic hormone (ACTH) is one of several hormones produced in increased amounts from the abnormal pituitary gland in PPID- affected horses and ponies. We can measure ATCH levels in a simple blood test and a positive diagnosis is made when these rise above a certain point.

A study by Victoria Copas and Andy Durham last year at Liphook revealed that ACTH secretion can vary from month to month. There are higher levels in non-affected horses during the months of August, September and October. This means we use higher cut-offs for diagnosing PPID from August to October compared with November to July. In the case of a borderline result, vets may consider dynamic tests to confirm a diagnosis. The most common of these is the TRH stimulation test, which triggers the release of especially high levels of ACTH from the pituitary gland in PPID cases.

Since PPID is caused by age-related nerve degeneration, it follows that as a horse gets older the likelihood of a positive diagnosis increases. Originally, researchers though that the disease only affected geriatric horses. Until recently, there were few reports of PPID in horses under 10 years old and it was debatable whether to bother testing horses in this age group. The latest research has altered this point of view. Post-mortem examination of horse in the under-10 age bracket has revealed that some do indeed have PPID. As simple diagnostic tests have become available, younger horses with the most subtle symptoms have been tested and confirmed as positive. Testing for all laminitis cases fir PPID should therefore be considered – no matter what the horse’s age.

Reducing the laminitis risk

We know that many PPID cases are at risk from laminitis. This risk is persistent if the xraydisease is left uncontrolled, so the treatment is aimed at reducing both the chances of laminitis and the severity of the other associated clinical signs. The only medication licensed for the treatment of PPID in the UK is pergolide mesylate, otherwise known as Prascend. Pergolide inhibits the abnormal development of the pituitary gland, which may stop further enlargement of the abnormal tissue present and reduces the hormone levels that are subsequently produced.

Pergolide is considered a safe drug. The most common side effect is a loss of appetite when the treatment is started. This often resolves when pergolide is stopped and then restarted at a lower dose before being increased more gradually. Concerns that the pergolide may cause liver disease have been disproven.

There is some individual variation in the response to pergolide therapy. When obvious PPID signs such as lethargy, excessive hair growth and increased thirst and urination are resolved, we might assume that the disease is under control. But where the clinical signs are less defined, we cannot rely on the outward symptoms to judge if the pergolide dose is correct. In all cases, follow up blood tests will give a good indication of the drug’s efficacy. If the ACTH levels remain high, an increased dose may be necessary.

There is no evidence at this time that any herbal supplements can effectively control PPID. So what is the prognosis for a horse diagnosed with PPID? Unfortunately, the degenerative, age-related nature of the disease means that it can only be controlled rather than reversed. But with early and appropriate treatment, the horse may have many active years ahead.

The most likely cause of death in PPID cases is the development of laminitis, so survival is more likely if the disease is treated effectively and the laminitis risk is reduced. Studies have also revealed that PPID survival rates are lower if high levels of insulin are also present. What’s reassuring for horse owners is that high blood insulin levels can be controlled with diet management changes made under the guidance of the vet.

Unblocking the pipes

If you’ve ever suffered from sinusitis, you’ll know it can cause anything from a runny nose to rotten headaches and painful facial tenderness. Sinus disease can affect horses, too, with varying degrees of severity. Some cope well, whereas in others in can cause considerable discomfort.

The disease is poorly understood, yet it has significant consequences for welfare. It’s runny noseeasy to imagine than an affected horse could feel uncomfortable when tacked up and ridden, or experience pain when he puts his head down to graze. Sinus disease has been suggested as a possible reason for headshaking, poor performance and behavioural changes. This makes prompt diagnosis and effective treatment all the more important. But why does sinus disease develop – and how should we tackle the condition if it takes hold?

Understanding sinusitis

If a horse’s skull were made of solid bone, it would be too heavy to lift off the ground. Instead, several large, air-filled cavities – collectively called the Para nasal sinuses – make the head a more manageable weight so the horse can move at speed. These cavities are lined with mucous membranes that continually secrete mucus; this clear discharge drains naturally into the nasal cavity through small openings. When sinuses become inflamed, however, the normal secretions become thicker and the drainage system starts to block up. The discharge then becomes infected and pus collects in the sinuses, leading to sinusitis and a horse with a sore head.

In an attempt to better understand sinusitis disease, vets from the Edinburgh and Glasgow veterinary schools last year published one of the largest studies to date. Over a 12-year period, they reviewed 200 cases of equine sinusitis referred to the equine hospital at the University of Edinburgh. These were not straightforward and easily treated cases but more complex problems that were therefore more likely to require surgery. Tackling the different types of sinus disease has historically been fraught with difficultly, with many cases requiring prolonged or multiple treatments.

trephineBut the study revealed that the long-term success rates for treating the majority of these disorders have improved markedly over the past decade. Researchers found that 87% of cases had complete and long-term remission of all symptoms. A further 6% experienced partial remission – proof that treatment methods for equine sinus disease are now more effective.

Primary sinusitis is the most common of all the disease variations. Its exact cause remains unknown, but it is thought that a viral infection or a bacterial disease such as strangles can damage the lining of the sinuses and interfere with the normal clearance of mucus. This was the most common of the case studies in the Scottish veterinary school survey. Dental disease is the most common cause, affecting almost a quarter of cases in the study. Because the tooth roots extend into the maxillary (upper jaw) sinus, an infected or damaged tooth can also compromise the sinus, the resulting sinusitis can drag on for months, unless the affected tooth is removed.

Sinus cysts were responsible for 13% of the cases studied, followed by trauma from an injury to the head. Tumours, which accounted for 5% of cases reviewed, usually have the worst outcome, as some are inoperable. The two most unusual causes are fungal infections of the sinuses and haemorrhagic polyps, otherwise known as progressive ethmoid haematoma.

Clearing the airways

With multiple cases, each with a different prognosis it is important to establish exactly scopywhat is wrong. An endoscope is a vital tool for confirming that the discharge comes from the sinuses. Sinoscopy, where an endoscope is used to examine inside the sinuses, is even more effective, a tiny hole, known as a trephine, is drilled through the bone of the skull overlying the sinus so the endoscope can be inserted. This can be done in the conscious horses with the aid of local anaesthetic and is tolerated surprisingly well.

Sinoscopy is only an option if the sinuses are not already filled with mucous. Otherwise, they’ll need to be emptied first by lavage (flushing) or suction. An X-ray is useful even when there is fluid within the sinuses. It will reveal dental disease and soft tissue masses such as cysts or tumours. A bone scan may be necessary, however, to differentiate between dental and primary sinusitis.

Treatments will vary depending on the cause. Around 60% of human bacterial sinusitis cases resolve spontaneously without antibiotics. It is likely that many acute cases of equine primary sinusitis will also need no medication. But the longer the condition persists, the more serious the problem becomes.

diagramMucolytics, which dissolve thick mucus and old-fashioned inhalations, are still sometimes used to help shift muck and pus and restore the normal drainage mechanisms. Light exercise helps encourage the sinuses to clear. If initial treatment fails to clear the nasal discharge a more radical nasal treatment is sometimes required. Flushing the sinuses several times a day with large volumes of fluid is commonly performed via a tube placed in the sinus.

In chronic cases, more invasive and surgical techniques may be necessary to remove solidified discharge. The vet will usually create a bone flap in the skill to gain better access to the affected sinus. Enlarged drainage holes are sometimes opened up surgically, too, which works well in most cases with surprisingly little scarring.

In the future, more widespread use of advanced imaging techniques such as CT and MRI may further enhance sinus examination and allow more focused early management. It’s worth contacting your vet if a runny nose remains present for any length of time, especially if the discharge is just from one nostril.

Nosebleeds – when to take action

The sight of blood dripping from a horse’s nose can cause panic. But nosebleeds are a common problem and not necessarily something to worry about. Very occasionally, however, a nosebleed can be an early sign of something more sinister. While a minor, one-off bleed from one nostril may not warrant calling a vet, anything persistent or more frequent definitely requires investigation by a vet.

A common cause of nosebleeds is trauma, such as a bang to the head or from the nosebleedpassage of a stomach tube up one of the nostrils. Typically, a moderate amount of blood will be coming out of one nostril and the flow will stop of its own accord within an hour or so.

Other causes of bleeding from one nostril include nasal masses. These can range from small polyps to large tumours and tend to cause intermittent and moderate bleeds. The amount of blood will be less in the cause of an ethmoid haematoma, but these small bleeds may recur frequently over a long period of time.

Frequent bleeding from either one of the nostrils, or both, could point to a more serious underlying illness, such as thrombocytopaenia – a low level of platelets, which help the blood to clot. The amount of blood will be variably, with no particular pattern to occurrence or length of bleed.

Another possibility is exercise-induced pulmonary haemorrhage (EIPH). This can produce a variable amount of blood, usually out of both nostrils, after a significant period of exercise. The most useful diagnostic aid in investigating the cause of a nosebleed is endoscopy, which allows us to see where the blood is coming from. Video endoscopy, in which the image is seen on a screen, rather than down the more basic fibre optic scope, can often be done at a yard or clinic. Recent advantages in diagnostic imaging mean that we can now glean a huge amount of information from a CT scan, although this would be reserved for less obvious cases.

Emergency scenarios

nosebleed1A nosebleed rarely requires immediate veterinary action, but one emergency scenario is an arterial bleed. If an artery has ruptured, blood will not be trickling from the horse’s nostrils – it will be pumped out at an alarming rate. A blood loss of more than 30% can be fatal. For a 500kg horse, this would equate to about 15litres, or a full water bucket.

Up to this volume, most horses can cope with a relatively large loss of blood. Blood will be diverted to essential organs, the heart rate will increase and the horse will also have the urge to drink substantial amounts of water to compensate. An arterial haemorrhage can occur if the horse falls over backwards and hits his head. This can tear or detach the longus capitus muscles attached to the base of the skull, fracturing the basisphenoid bone. A more common cause of this type of bleed, however, is guttural pouch mycosis (GPM).

GPM is a fungal infection in the guttural pouches – air chambers situated in the neck just behind the skull 0 that are unique to the horse and whose function is not fully understood. In GPM, the fungus frequently grows on the wall of the internal carotid artery at the back of the guttural pouch. As it develops it eats into, and then right through, the artery wall. It’s important that owners are aware of GPM and that any substantial nosebleed is investigated promptly. What starts out as a relatively harmless –looking bleed can be an early indicator that a massive and potentially fatal haemorrhage is about to occur. Left untreated, the horse can bleed to death.

Immediate action is crucial

Endoscopy of the guttural pouches is usually adequate to diagnose GPM. Once diagnosed, the horse should be taken immediately to a specialist equine surgical facility for treatment.

There are a number of ways to prevent the bleeding. The most straightforward is to nosebleed2ligate or tie the internal carotoid artery. The anatomy of the circulation in the region of the guttural pouch, however, is very complex and occasionally bleeding can continue, despite ligation.

More complicated techniques include transarterial coil embolization, where a small coil is inserted into the artery to encourage the blood to clot, and balloon catheter embolization, where the same effect is achieved using a tiny expandable balloon. Both techniques require fluoroscopy – or real-time X-ray imaging – and the use of highly specialised equipment available at only a few specialist centres.

Time is very limited with GPM. The emergency of these cases means that ligation of the artery is usually the most effective and practical treatment. Ligating the blood supply causes the fungus to die – a process that is not guaranteed, yet seems to happen most of the time. We also treat it topically with antifungals administered via a catheter into the guttural pouches.

Treatment and check-ups may be on-going for some months. While prognosis is guarded, most successful surgery results in the horse making a full recovery. GPM may be dramatic and potentially fatal, but thankfully it is not common. It is not infectious to other horses and there are no known reasons why one horse contracts it and another doesn’t. The fungus is present everywhere. As far as we know, there is nothing that can be done to reduce the chances of a horse developing the condition.

Owners can, however, be vigilant to the treat by seeking immediate veterinary attention in the case of a substantial nosebleed. Early action could be a lifesaver.

Tapeworm – the enemy within

This week, Horse and Hound magazine looked at tapeworm in horses, coming up with some interesting developments of it over the past couple of years.

Once thought relatively benign, the tapeworm is now known to be a potential danger. Ofanoplocephala-perfoliata-egg-7616 the three tapeworm species affecting horses in the UK, the most common is Anoplocephala perfoliata. The pale-coloured parasite has a flat, segmented body and measures around 5-8cm in length once fully grown. Unlike other worms in the horse, the tapeworms develop inside an intermediate host – the microscopic forage mite. Horses become infected when they eat hay or grass containing these mites, which are themselves infected with tapeworm larvae. These then develop into adult tapeworms inside the horse’s intestines.

Once laden with eggs, segments of the tapeworm’s body detach and are passed out of the intestines in the horse’s droppings. The eggs are released into the pasture where ingested by forage mites. The life-cycle takes from three to six months to complete. Owing to our temperate climate, the UK’s horses are particularly susceptible to tapeworms. Some horses are more prone to infection than others. In fact, 80% of intestinal parasites reside within just 20% of the equine population. While young and geriatric horses are at greater risk from heavy burdens, tapeworms can lurk within any animal. What’s worrying is than an apparently healthy-looking horse can be harbouring a large build-up of these potentially lethal visitors.

Blocking the intestines

tapewormsfAdult tapeworms can be found at the narrow intersection between the small and large intestine called the ileocaecal junction. Here, they attach themselves in clusters to the mucosal lining of the digestive tract, using four suckers located on their head. If they build up in large numbers at this junction, tapeworms can cause inflammation that alters the movement of the intestines.

It is now known that infection with tapeworms is associated with an increased risk of colic, particularly spasmodic colic (a type I have experienced when my own horse got it at a competition – very worrying! ) or a blockage at this narrow junction known as ileal impaction. Another risk is intussusception, in which one portion of the gut telescopes into another and becomes stuck. Surgery is sometimes necessary.

Research at the University of Liverpool revealed that 80% of ileal impaction cases and 22% of spasmodic colic cases were due to tapeworms. Ensuring your horse is free of tapeworms will therefore reduce the risk of colic.

A ticking time-bomb

Testing for tapeworms can be tricky. Horses can have large tapeworm burdens and lifecycleappear healthy on the outside. Counting the tapeworm eggs in a faecal worm count (FWEC) is unreliable. Egg numbers are usually low and encased in the segmented tapeworm part rather than distributed evenly throughout the droppings. A negative result on a FWEC does not therefore mean your horse is free of tapeworm.

Instead of a FWEC, we can use a blood sample for infection, a method known as the ELISA or tapeworm antibody test. A horse with a high level of tapeworm infection will produce a large number of antibodies, which can be detected in the blood. The test indicates a broad level of intensity, rather than tapeworm numbers. The amount of antibodies will indicate whether the burden is low, medium or high.

While the blood test is useful for assessing whether your horse has been infected with tapeworms in the past, it is not a reliable indicator of response to treatment. This is because it takes around four to five months for the antibody levels to return to normal after the worms have been killed. Therefore the test only needs to be carried out once a year.

Horses with evidence of a high tapeworm burden on a blood sample are likely to be susceptible to infection with tapeworms in the future. The should be treated a second time that year, before being retested 12 months later.

Treatment options

horses-grazingThere are two different approaches to tackling tapeworm. Treatment can be targeted, following a blood test, or administered within an annual worming regime.

With targeted treatment, your vet will combine information on the horse’s worming history with FWEC and blood test results to decide whether he needs worming – and the most appropriate treatment if this is necessary. Targeted treatment can reduce the likelihood of worms becoming resistant to treatment and identifies horses at risk of high levels of worm infection. Using this method, horses are blood-tested for tapeworms once a year. Those with a high burden are treated after the test and then again six months later. The blood sample is then repeated the following year.

New horses on a yard should have a blood test or a FWEC, or be treated for both tapeworms and roundworms, before they are turned out with others. In some yards, targeted worming may not be suitable nor practical. In these instances, it is best to treat for tapeworms every six months.

Tapeworm infection is not linked strongly to seasonality, so the time of year that treatment takes place is not particularly important. A risk is higher after prolonged periods of grazing, however, it seems wise to treat at the end of a summer out at grass.

It is important to be aware that not all wormers kill tapeworms. The parasites can be treated with one of two drugs – praziquantel and pyrantel. The latter must be at a double dose. Fortunately, both drugs are very effective and cause death and detachment of the tapeworms from the gut wall within 24-48hr following treatment. They are available as single products or in combination with other drugs that target different types of worms. Parasite populations on the pasture  can be reduced by regular removal of droppings, resting grazing and rotating sheep and cattle on to horse fields.

To conclude, careful pasture management  combined with correct testing and treatment will ensure that tapeworm infection is controlled. For me, having moved around to different yards, I found it very interesting that not once were my horses, or new horses coming onto the yard I was at, were testing for tapeworm. Upon  moving, you are subject to the current worming cycle that yard operates on, meaning that if new incoming horses are infected with tapeworm, the chance of them spreading is increased if they are turned out immediately with other horses.

Hope you found this article interesting, more next week!

Overcoming a bad start in life

After going through the breeding process, nothing is better than seeing a proud mother foal birthwith her healthy foal. However, despite the best management, problems can and do occur. In the case of a weak or a wonky newborn, the race is on to nurse the foal through the crucial early days when the chances of survival can be slim. But if the initial – and often costly – treatment is successful, what about the future? Can an ill or injured foal become a sound athlete, or must a shaky start mean problems later in life?

Counting the cost

When making decisions about treating a sick foal, owners need to have some understanding of the long-term consequences of the disease or condition – especially in the current economic climate. Most research into the subject has focused on thoroughbreds and whether foals that have been sick in the early months of their lives are less likely to fulfill their potential on the racecourse.

A study carried out at Anglesey Lodge Equine in Co Kildare in 2010, however, took a slightly different tack. It sought to assess whether hospitalisation of thoroughbred foals in the first four months of life would adversely affect future sales performance. The study involved 63 foals, 53% of which were admitted to hospital in the first week of life with common conditions including diarrhoea, septic joints and pneumonia.

Of the group, 30% went to auction as foals, 62% as yearlings and the remainder were sold as two-year-olds. Their sale prices were compared with 378 control animals of similar pedigree going through the ring at the same time. The previously sick foals reached comparable sale prices to animals with no history of early sickness. This indicates that poorly foals are not necessarily disadvantaged in later life.

The study did not look at whether hospitalised foals were likely to reach public auction. We can glean some indication of the chances of a sickly foal fulfilling early potential from previous research carried out in the USA. Studies there revealed that 6% of foals formerly hospitalised remained unregistered following discharge, compared with a population average in the region of 1%.

Most studies involving breeds of all kinds look at even shorter-term outcomes – that is, whether the foal survives until hospital discharge. Few consider the long-term outlook for sport horses, as opposed to thoroughbreds. In part, this is due to the fact that most thoroughbreds are destined for the racecourse. Their history at sales and in racing can be traced easily through Weatherbys. For sport and pleasure horses, however, intended use is diverse and performance and sale results are not readily available. This makes obtaining reliable, objective long-term data much more difficult.

The critical early days

The first weeks of a horse’s life is considered to carry the highest risk of mortality. the newborn foal is susceptible to a range of potentially life-threatening diseases including septic arthritis (joint ill), septicaemia – often associated with inadequate ingestion of antibodies from the first rich milk or colostrum – and congenital conditions such as severe limb deformity. The bones of a foal can heal surprisingly well and early fractures do not necessarily limit the future performance. The outlook is much worse, however, when the fracture extends on to the weight-bearing area of a joint or infection damages the joint cartilage.

Septic arthritis and the bone infection osteomyelitis can carry long-term implications. While aggressive treatment early in the condition can significantly affect outcome, a UK study indicated that even a single infected joint can adversely affect the long-term athletic potential of racehorses.

Some diseases produce alarming symptoms, as in the case of perinatal asphyxia syndrome, which can cause problems such as convulsions, diarrhoea and an inability to stand and suckle. As long as the case is uncomplicated by infection, howeverm around 80% of foals affected are successfully discharged from hospital. The condition is though to have little impact on the foal’s long-term prospects.

A difficult decision

Foals are remarkably resilient, the downside being that health problems can be difficult to spot. The horse’s evolution as a prey species means that the foal – the most vulnerable member of the herd – will rarely show obvious signs of illness until a disease process is relatively advanced.

Vigilance is key. Long-term prospects are greatly improved if a problem is detected in its early stages and appropriate treatment started as soon as possible. As this can also influence the size of the vet bill, it pays to act immediately if something seems amiss.

Although advances in veterinary and surgical techniques are giving many of these foals better chances, a particular vet’s experience with foal problems can play a crucial role. More complicated cases tend to fare better at equine hospitals with experience staff, so an early referral will help.

Deciding whether or not to persevere with a sick foal is not easy, Treatment is often labour-intensive and costly, with the added risk of complications. Foals are rarely insured for vets’ fees and there are strict conditions for a mortality claim. Consider, too, whether you can provide the facilities for convalescent care, such as an exercise pen or nursery paddock, and specialised farriery or physiotherapy where necessary.

While there’s certainly potential for a poorly foal to grow up into a fit and healthy adult, its wise to know what’s involved before embarking on the journey.

 

Hope you enjoyed this article, I previously knew little about breeding so it was interesting for me to look into. More next week 🙂