Equine metabolic syndrome (EMS) and laminitis

Ponies are genetically predisposed to EMS. Obesity in ponies is common due to a thrifty genotype combined with rich food and less exercise, this leads to a high EMS incidence.

Pony origins and working background

• Originally, Welsh ponies, cobs and Shetland ponies were working ponies used to pull carts, carry people or for hard labour in the coal mines.
• They lived in harsh climates with lush quality pasture for a small part of the year and sustained themselves on poor nutrient, native pastures. 
• These ponies developed a thrifty genotype with this survival and selection pressure.

Ponies in Australia

• In Australia, these ponies experience a kinder climate, are often rugged and in the good years have access to quality, lush pastures for most of the year and are fed concentrates. 
• They no longer burn calories by pulling heavy carts daily or are used in coal mines. 
• They are ridden on weekends and shown for part of the year, or become paddock pets when outgrown by children.
• Their lifestyle is more luxurious and slow paced.

• The genetic predisposition for EMS in ponies means these individuals can't tolerate being overweight.
• When you combine a pony's genetic predisposition with obesity it can quickly lead them towards EMS and laminitis.
• It's important to know that laminitis can often be very insidious and subtle. You may even think 'he's a bit sore after farriery' where the pony may in fact be walking around on a barely hanging on toenail.
• Equids only have four toenails to walk on. If a 250kg pony is 50kg overweight it can make a difference to the toenail or hoof becoming permanently deformed or completely detaching.
• It is crucial to avoid overweight and obese ponies.
• Obesity is not the only trigger. Occasionally, we see EMS in leaner ponies and horses.
• We are still learning about the condition and its triggers. 

You can evaluate obesity in your pony or horse by measuring its:

1. Body condition score (BCS)

• BCS determines your horse's overall obesity.
• It is important to feel for the bones and how thick and squishy/firm the fat deposits are.
• Standard BCS is scored from 1-9. Ideal BCS is 5-6/9. Many show ponies have a BCS of 7-9/9.

2. Cresty neck score (CNS)

• CNS evaluates localised fat deposits (around the nuchal ligament of the crest).
• CNS is scored from 1-5. Ideal CNS is 2/5.
• Often stallions have a larger crest, and a higher score is acceptable for them.
• It's not uncommon for ponies and cobs in show condition to weigh more but it's important to note the difference in fat deposits vs muscle mass. Anything on top of the crest is fat and not muscle.

Detailed scoring systems are available from Queensland University of Technology:

• How to estimate a body condition score
• How to assign a cresty neck score

EMS is characterised by:

1. metabolic imbalances, especially in insulin regulation (known as insulin dysregulation or ID).
2. obesity
3. laminitis

Insulin dysregulation can be:

• insulin that is too high in the blood (hyperinsulinaemia) or
• insulin that is not working correctly on the body's cells to reduce blood glucose levels (insulin resistance).

Equine medicine specialists and many equine general practice veterinarians can evaluate your pony or cob and test for EMS.

At UQ VETS Equine Specialist Hospital, we test for EMS by:

• conducting a thorough clinical examination
• evaluating laminitis (often with X-rays)
• assessing BCS and CNS
• routinely performing metabolic testing to evaluate insulin and glucose dynamics.

Testing for insulin dysregulation

• As insulin dysregulation is the core component of EMS, we test for excessively high insulin and insulin resistance.
• A single blood sample can measure insulin, but it does not mimic what is occurring in response to a meal.
• We strongly recommend conducting more sensitive dynamic tests to evaluate what is occurring in response to food.
• Common tests we perform are the oral glucose test (OGT) and oral sugar test (OST) which involve giving glucose powder or sugar syrup orally and measuring glucose and insulin 1-2 hours later.
• These tests are very safe to perform and are performed almost daily by some equine veterinarians.

Testing for PPID

• A separate disease such as Pituitary Pars Intermedia Dysfunction (PPID) also known as Equine Cushings Syndrome, can also influence ID and compound the risk for endocrinopathic laminitis.
• If your pony or cob is older (>12 years of age), especially if they have any change in hair-coat shedding, we also recommend a conversation with your vet regarding testing for PPID.

There is alot you can do if your pony or horse is diagnosed with EMS to reduce the risk of laminitis. You can work closely with your veterinarian to reduce the laminitis risk but your pony or horse's diet is key.  There is no quick fix or magic pill. 

Diet

• Diet composition and obesity are the main drivers in your genetically predisposed pony's weight loss. 
• Feeding your pony a diet low in carbohydrates is crucial.
• As a general rule, we recommend feeding 1.5% of body weight in roughage that is low in non-structural carbohydrates (<10% NSC content).
• You'll need to weigh the hay. Luggage scales work really well. Every biscuit within a bale does not need weighing, but new bales or cuts definitely do because there can be significant variation in weight per cut of hay.

NSC content

• The NSC content in hay can vary significantly (see table below).
• Generally, Teff hay has consistently low NSC content, but if it is unavailable, soaking Lucerne or Grassy hay for an hour (and rinsing off after) is sufficient.
• It's best to completely remove ponies from pasture and grass because its hard to quantify how much they're eating at pasture.
• On good quality pastures, a pony can eat enough to fuel a racehorse in 3 hours.  Locking them up for only part of the day means they will often eat twice as fast when allowed back onto the pasture.
• It's important not to feed your horse or pony tidbits, apples, carrots, liquorice, or bread scraps because it all adds up.
• Ideally your feed stuffs can be tested which can usually be organised at your local Agriculture shop.
• These are general feeding recommendations, and a tailored plan is often needed by working with your veterinarian.

Exercise

• Exercise is proven to improve insulin sensitivity and can help reduce fat and build muscle mass.
• We do not recommended exercise during and in the recovery phase of laminitis.
• Working with a master farrier experienced with problem hooves can do wonders for the pony’s comfort and encourage healthy new hoof growth.
• Simple is often best and many horses and ponies do not need fancy shoes and boots.
• In many cases trimming based on hoof radiographs can make an enormous difference to successful return to an athletic career. 
• It's important that your farrier and veterinarian working together.

Medication

• If the diet is very strict, but your pony still has ongoing issues we may recommend medication.
• Your veterinarian may test the pony’s insulin values again after it consumes a new low-sugar diet to see if the medication is appropriate. Ideally insulin is again measured while your pony or horse is on medication to see if it is working.
• Medications used to help manage EMS include metformin and levothyroxine, both human drugs.
• Metformin is used to assist in reducing the amount of sugar absorbed from the intestine and levothyroxine helps to increase the pony’s metabolic rate and lose weight.

What we know

• Ponies are genetically predisposed to EMS.
• By managing dietary changes, reducing obesity and fat stores we can manage EMS in these individuals.  
• Reducing or eliminating laminitic episodes allows these ponies to lead a comfortable and sound life by being a competition pony, breeding stallion, brood mare, pony club mount or paddock pet.

We can only diagnose ponies for EMS using insulin testing at this time.  Genetic testing is a long-term goal but is years away.  UQ research is working to identify at risk individuals before they develop the disease to guide management, environmental and breeding decisions. 

UQ research 

• Our UQ research team is investigating if certain lines of ponies are more predisposed to EMS than others.
• Through large scale genetic tests, part of our United States team recently found a genetic mutation in the HMGA2 gene that was correlated with higher insulin values in Welsh ponies. 
• We are determining if this holds true for Welsh and Shetland ponies in Australia.

Changing show standards

• The ideal BCS for longevity and athletic performance is 5-6/9.
• Many have grown to accept a cuddly BCS of 7-8/9 as 'show condition.'
• Body fat in ponies can be used to hide conformation faults. 
• Many ponies have EMS and overfeeding leads to high blood insulin.
• Increased body weight on small feet puts these ponies at great risk of the devastating and painful condition of laminitis.
• It may be time to reset what is considered 'ideal' in the show ring.
• If 5-6/9 became the new ideal 'show condition' then our ponies would be more athletic and live happier and healthier lives.