Professor Andy Durham, a vet from the Liphook Equine Hospital in Hampshire, discusses the links between laminitis and possible underlying hormonal diseases.
Laminitis
The vast majority of laminitis cases are associated with equine metabolic syndrome (EMS) and PPID (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 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.
Disease prevention
Increased risk of laminitis 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.
Identifying risk factors
Grazing plays a role in triggering laminitis and the risk increases with age, at certain times of the 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 factors 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, 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.
What horses are affected?
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 tests 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 measures 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.
Important tests
A variety of tests may be used to help diagnose EMS and PPID. 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.
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.
The Talk About Laminitis disease awareness initiative, which is supported by Redwings, The British Horse Society and World Horse Welfare, is offering free laboratory fees for the ACTH test until the end of October. For further information click here.
About the expert
Professor Andy Durham has been in equine practice for 28 years and has always had a particular interest in laminitis and the hormonal abnormalities that can cause it. For the last 22 years, Andy has worked at Liphook Equine Hospital in Hampshire.