Professor Andy Durham discusses the links between laminitis and underlying hormonal diseases
Laminitis is a particularly upsetting disease for so many reasons. It is common, it is painful, it may result in euthanasia, and perhaps most upsetting of all is that, for the most part laminitis is preventable.
The vast majority of laminitis cases are associated with equine metabolic syndrome (EMS) and pituitary pars intermedia dysfunction (PPID – usually referred to as PPID or equine Cushing’s disease). EMS sufferers are susceptible to laminitis as a result of varying combinations of breed, excess body fat, inappropriate diet and lack of fitness.
Horses and ponies with equine cushing’s disease have an overactive pituitary gland, with laminitis as a possible consequence. Identification of these conditions enables specific control measures to be applied to reduce the future risks of laminitis.
This article will explain how these conditions relate to laminitis, how to recognise them and how to control them.
Laminitis has been recognised for centuries and it has long been known that certain common features are shared by many affected horses and ponies. Increased risk of the disease is apparent in, for example, native types and those that are overweight, receiving little exercise and grazing lush pastures, especially in late spring and early summer when grass is richest.
Awareness of these characteristics might not be new, although a surge of research over the last 10-15 years has brought much attention to these causal elements and attempted to explain how they relate to the risk of laminitis in susceptible individuals.
A focus on the causes of laminitis, rather than just dealing with the consequences, will hopefully allow us to prevent many more potential future cases. It would be wrong to suggest that this job is now done and we have all of the answers to eradicate the disease. However, it is fair to say that with a firm will, determination and some effort, we should be able to greatly reduce the occurrence of laminitis and lower the chances of it recurring in affected horses and ponies.
We like to see our horses and ponies grazing rather than confined to their stables. It is surely more natural – they enjoy it, their health improves from the fresh air and grass and it is also good for their psychological wellbeing. These general benefits may be true for most equines but, in marked contrast, turnout can be incredibly harmful or even fatal in those susceptible to laminitis. It is a remarkably strange scenario where the same grazing for two members of the same species could be a benefit to one and a killer for another.
Identifying risk factors
Clearly, grazing plays a role in triggering laminitis. But the fact some are susceptible (for example a fat, unfit native pony) whereas others appear not so (such as a fit and lean competition horse), tells us there must be factors within each individual that affect whether or not he might get laminitis.
It is up to you and your vet to identify and control these factors in your horse or pony. So what does increase the risk of laminitis in a grazing horse or pony? The risk of laminitis increases with age, at certain times of year (late spring/early summer) and is also increased in certain breeds and types due to genetic factors, although there is little you can do to change those in your pony!
The main specific causal factors that are within your power to control include diet, body fat, lack of exercise and additional problems such as PPID. What appears to link these factors with laminitis is the hormone insulin. Insulin is produced after eating sugary feeds and is an important hormone with many actions around the body. However, following several key studies conducted by researchers in Australia, it is clear that abnormally high blood insulin concentrations are harmful and will directly trigger laminitis in horses and ponies. As blood insulin levels are known to be influenced by factors including age, season, breed, diet, body fat, fitness and PPID, this makes sense in understanding why these are commonly associated with laminitis.
“It is a strange scenario where the same grazing for two members of the same species could be a benefit to one and a killer for another”
Although the classic image of an EMS case is a fat native type, and a classic PPID case is an elderly individual showing an excessive hair coat or delayed seasonal shedding, neither of these pictures is very consistent.
EMS may arise in many different breeds and types (it is common in warmbloods, for example) that are not necessarily obviously overweight. Similarly, we now recognise PPID in remarkably young horses and ponies and their coats are often normal.
Thus, with few exceptions, horses and ponies suffering from laminitis are deserving of close examination and laboratory testing to determine whether EMS and/or PPID are actually present. This then allows focus on the specific underlying causes of the laminitis to reduce the risks of further attacks. Evidence indicates that at least 90 percent of laminitis cases will be found to have an underlying hormonal abnormality – so performing tests for these conditions is far from a ‘long shot’!
Action following diagnosis
When a diagnosis of EMS and/or PPID has been made, it is absolutely crucial that specific countermeasures are applied to reduce the risk of further laminitis attacks. Principles of PPID control are relatively simple as pergolide (marketed as Prascend) is the only drug approved for this purpose.
Dose rates are calibrated by veterinary surgeons on a case by case basis but pergolide appears highly effective in controlling PPID in the vast majority of cases. Occasionally, some horses might lose their appetites after starting the drug but this is generally only temporary. It can usually be avoided by a very gradual introduction and increase up to the required dose. Drug treatment with metformin and/or thyroxine might also be useful in EMS cases, although the most important aspect of dealing with this condition is dietary control and increasing exercise. Several research studies have enabled us to offer very specific dietary advice in EMS cases, which has been shown to help improve insulin regulation and reduce laminitis risk. This requires teamwork and veterinary supervision for careful monitoring and fine tuning of the diet according to response and also firm commitment from the owner. The important message is that weight loss and reduced laminitis risk can be achieved even in the toughest of ‘good-doers’. Control of EMS may not be easy, but it is possible! The stark choice is: deal with the problem and take on the challenge in a disciplined fashion, or let things carry on as before and accept the pain and distress of recurrent laminitis and ultimately the potential loss of the horse or pony.
Remember that if you always do what you have always done, then you will always get what you always got. If you want to prevent laminitis recurring, as hopefully all owners would, then things must change!
A variety of tests may be used to help diagnose EMS and PPID. Some tests are specific to each individual disease, whereas others are applicable to both EMS and PPID cases. In addition to diagnosing the diseases, the tests are also useful for monitoring the response to treatment and management changes. ACTH is one of several hormones produced by the pituitary gland and is the preferred test for PPID. This is measured in a simple blood test which detects most PPID cases, although there are some that the test might miss. Where doubts exist, a further test known as a TRH stimulation test can be used to confirm any cases of PPID not identified by standard ACTH testing.
Analysis of blood samples for a hormone called adiponectin, has become available at the Liphook Equine Hospital Laboratory. Adiponectin is a beneficial hormone released from fat that is involved in insulin regulation and inflammation. Failure to produce adiponectin appears to be an important link between EMS and laminitis.