LAMINITIS IN HORSES AND PONIES

Why too much fresh grass might be dangerous for your horse or pony.


Valerie De Clerck, Doctor of veterinary medicine



Laminitis is a very painful and emergency condition of the feet in horses and ponies, caused by a problem elsewhere in the body. It is frequently seen in spring as it is often associated with high amounts of sugar and fructans in lush pasture and can be further complicated by many other factors such as obesity and insulin resistance.



WHAT IS LAMINITIS in horses and ponies?


Laminitis literally means "inflammation of the laminae", however damage to the laminae in the hoof is a better definition as the inflammation of the lamellae is often a consequence rather than a cause. 


The laminae have a very important function in the hoof as they attach the coffin bone to the inside of the hoof wall. These laminae bear much of the weight of the horse. In horses with laminitis, the lamellae are damaged and start to detach. In severe cases, the coffin bone and the hoof wall separate and the coffin bone sinks and can even penetrate the sole. 

drawing of the loosening of the laminae in the feet of a horse with laminitis

Figure 1: on the left: loosening of the laminae that secure the coffin bone to the hoof wall; on the right: the coffin bone sinks and penetrates the sole.


WHAT IS CAUSING LAMINITIS in horses and ponies?


Several conditions have been associated with laminitis and laminitis is always the consequence of a problem elsewhere in the horse's body. However, survey studies indicate that most laminitis cases (61%) occur in horses and ponies kept at pasture. Eating large amounts of grass is therefore not the direct cause, but it is often the trigger.


Certain horses or ponies tend to be affected more than others, and susceptible animals are prone to recurrent episodes. Below we list the most common causes for laminitis in horses and ponies.


1. Poor blood circulation


Poor blood circulation is often associated with laminitis in horses. The blood supply can be disrupted by vasoconstriction, damage to the small blood vessels in the feet, excessive pressure in the hoof that cuts off the blood supply, or small blood clots (microthrombosis). 


2. Increased activity of degrading enzymes


The lamellar basement membrane in the hooves is continuously built up and broken down by certain enzymes (MMPs), when this balance is disturbed and the breakdown takes over, things go wrong and we are faced with laminitis.


brown horse grazing in fresh grass

3. Inflammation of the laminae


Inflammation of the laminae is a consequence rather than a cause of laminitis. Inflammation leads to swelling of the laminae, vasoconstriction of the small blood vessels, activation of the destructing enzymes (MMPs) and the release of free radicals. All of these have a negative impact on the health of the laminae and worsen the disease process.


4. Metabolic disorders and hormonal changes


Metabolic disorders causing laminitis are often related to insulin resistance. Insulin is an important hormone that regulates blood sugar levels by pushing sugar from the bloodstream into the cells. When a horse is insulin resistant, the body cells do not "listen" anymore to insulin and do not take up enough sugar. The sugar remains in the bloodstream causing the blood sugar level to increase. The body responds with increased insulin production, converting the excess sugar into fat. The horse will eat even more because it is hungry due to the now decreased blood sugar level. Eventually the pancreas becomes exhausted and can no longer produce enough insulin.


Insulin resistance is also a consequence of the disease PPID (Cushing), administration of corticosteroids and Equine Metabolic Syndrome.


5. Excessive weight


Excessive weight placed on one limb due to injury to the opposite limb is another cause of laminitis. The laminae of the weight-bearing foot must bear so much weight that the blood supply is compromised which has a negative impact on the health of the laminae.


RISK FACTORS FOR LAMINITIS in horses and ponies?


As already mentioned, there are several theories and causes associated with laminitis in horses. An underlying cause is always present, but usually there is then a final trigger that gives rise to clinical laminitis.


1. Pasture-associated laminitis


Laminitis is often associated with excessive consumption of grass with high levels of sugars. Fructan is one of those sugars produced by plants in the presence of sunlight. It is used to grow the grass, but if growth is not possible due to a cold ambient temperature, drought or lack of nutrients, the plant will store the excess sugar for later growth. This "stressed" grass with high levels of fructans is very dangerous for sensitive horses and ponies.

61% OF LAMINITIS CASES OCCUR IN HORSES AND PONIES KEPT AT PASTURE.


2. Digestive upset


As mentioned above, the most frequent cause of a sugar overload in the diet is too much fresh grass. However, grain overload or a sudden change in the diet are also risk factors for laminitis in horses and ponies. 


3. Toxic substances in the blood (endotoxemia)


Toxic substances can enter the bloodstream due to a change in the permeability of the intestinal wall, which allows the passage of toxins from intestinal bacteria into the bloodstream. This is called endotoxemia. Endotoxemia is often a complication in horses or ponies with severe colic or retained placenta. Other possible toxins are pesticides, drugs (corticosteroids), fertilizers, contaminated water, poisonous plants (e.g. Acorns), fungi in hay, ...


4. Overweight


Obesity and overweight in horses and ponies is often associated with insulin resistance. Obesity is therefore an important risk factor for laminitis in horses.


5. Genetic predisposition


Some breeds are at higher risk for laminitis such as the Appaloosa, the Welsh pony, the Shetland pony, the Dartmoor pony, the Exmoor pony, the Icelander, the Cob, the New forester, the Paso Fino and the Arabian.

Drawing of a horse with a typical stance of laminitis

Figure 2: typical stance of a horse with laminitis with the forelimbs placed abnormally far forward to release pressure on the forefeet. The weight is shifted towards the hind limbs.



HOW DO I KNOW IF MY HORSE OR PONY HAS LAMINITIS?


Clinical signs of laminitis usually start 24 to 72 hours following the onset of a septic disease process or after excessive grass or grain consumption. 


Laminitis is most often seen in the front feet, but it can affect all feet. 


The most common sign of acute laminitis is lameness and a very hesitant gait ("walking on eggs"). The horse or pony will often stand with the front feet stretched out to alleviate pressure on the toes (see figure 1). The temperature of the affected hooves will increase, and an increased digital pulse is palpable.

horse leg fingers measuring the digital pulse

Figure 3: How to feel the digital pulse in a horse (inside front leg)?


How can I feel the digital pulse of my horse or pony?


You can feel a horse's pulse on both his front and hind legs. 


 • In the front legs you can feel the pulse at the INSIDE of the fetlock or just below (see figure 3). Place your three fingers on the inside of the fetlock and try to feel a large vein. Just next to it you should be able to feel the blood pressure (digital pulse) of your horse or pony in the artery. Do not press too hard and do not use your thumb.


 • In het hind legs you can feel the pulse at the OUTSIDE of the leg just below the hock.

What to do when my horse or pony has laminitis?


1. Call your veterinarian!!


Laminitis is a medical emergency and very painful disease for your horse or pony so the first goal in the treatment is managing the pain (NSAID'S) and stabilising the feet


Your veterinarian might take x-rays to assess the position of the coffin bone and estimate the severity of the condition.

If your horse is older than 12 years it is recommended to have a blood test done to test for PPID.


2. Put your horse on soft bedding


Put your horse on soft and conforming bedding, ideally sawdust (soaked wood pellets), wet sand or shavings. If you put your horse on sand, make sure your horse does not eat the sand as this will cause sand colic!


You can provide additional support of the feet with special boots. Do not move your horse if he does not wants to walk himself.


3. Cool the feet of your horse


Acute laminitis is associated with inflammation of the laminae. Cooling of the feet is needed to reduce the inflammation and prevent loosening of the laminae. Put some ice cubes in a (plastic) bag and hang them around the feet. If you do not have any ice cubes, you can spray the hooves with cold water.


4. Change the diet of your horse


Remove your horse from grass (support the feet before moving!) and feed a low starch diet. Soak the hay and put it in a hay net or slow feeder. Adapt the amount of hay to the needs of your horse and remove grain from the diet. Supplement your horse with a good mineral supplement (with magnesium) and provide him with a salt block. 


 Make sure to always respect the daily nutrient requirements of your horse and consult your veterinarian or nutritionist to compose the diet. You can contact Ghent University for a detailed analysis or you can use the following website to estimate the concentration of different nutrients in the diet.



NEVER STARVE YOUR HORSE, BUT LET HIM LOOSE WEIGHT GRADUALLY.


STARVATION LEADS TO EXCESSIVE BREAKDOWN OF FAT, OVERLOADING THE LIVER AND RESULTING IN HIGH AMOUNTS OF FATTY ACIDS IN THE BLOODSTREAM. THIS IS A LIFE-THREATENING COMPLICATION!

It is also recommended to feed a supplement to balance the sugar- and fat metabolism and to support the liver. You can also support the blood circulation and strengthen the collagen in the laminae of the hooves. METABOLIC CARE is a plant-based feed supplement that combines these four features.


5. Hoof care


Hoof care is very important in horses and ponies with laminitis. The most important goal of proper hoof care is to redistribute the force of weight-bearing away from the hoof wall to the sole. This can be done by placing frogs or bars underneath the foot of the horse or pony and by placing your horse or pony on a soft surface. Sometimes it also helps to remove the shoes of the horse or pony. 


Consult your veterinarian and farrier to decide what the best solution is for your horse or pony.




how can i prevent my horse or pony from developing laminItis?


1. Pay extra attention to horses who had laminitis in the past


35% of the horses that had laminitis in the past relapse and often multiple times per year. 


2. Keep your horse in a good body condition


Aim to keep your horse or pony at a moderate Body Condition Score and prevent your horse or pony from becoming too fat, as obesity is a risk factor for laminitis.


3. Maintain a low-sugar diet (limit grain and grass intake)


Feed your horse a grain-free diet and limit the grass intake. Support your horse with a feed supplement to balance the sugar and fat metabolism, like METABOLIC CARE.


You can limit the grass intake by

1. limiting the time in the pasture; and 

2. using a grazing muzzle.


You should also check the fructan-index, before leaving your horse or pony in the pasture. Be very careful when the fructan-index is high! 

drawing of a horse with a muzzle

BEST TIME TO GRAZE


AVOID GRAZING


WINTER

BEST TIME TO GRAZE

AVOID GRAZING

 • when the temperature during the day and night is > 5°C and when it's cloudy.

 • when the temperature is < 5°C, especially when it's sunny; and

 • on a sunny day (< 15°C) after a frosty night.

SPRING & AUTUMN

BEST TIME TO GRAZE

AVOID GRAZING

 • Temperature between 5 and 15°C: best to graze in the morning

 • Warm & cloudy (> 15°C): afternoon & evening

 • Warm & sunny (> 15 °C): night and morning

 • on a sunny day (<15 °C) after a frosty night (0°C). The risk is highest in the morning;

 • on short and stressed grass; and

 • in the afternoon and evening when the temperature is between 5 and 15°C.

SUMMER

BEST TIME TO GRAZE

AVOID GRAZING

 • Warm & cloudy (> 15°C): afternoon & evening

 • Warm & sunny (> 15 °C): night and morning

 • in the afternoon and evening when it's warm (> 15°C) & sunny;

 • during periods of drought; and

 • on very short / stressed grass.

Based on info from hoefnatuurlijk.nl. This table only shows the influence of weather on fructan levels. Keep in mind hat there are other factors that have an impact on fructan levels, such as the type of grass, the soil, the availability of nutrients (more is more favorable) and the time of year.




SCIENTIFIC REFERENCES


1. Ivey JL. Pasture-associated laminitis.

2. Baxter GM. Lameness in Horses. Sixth edit. Wiley-Blackwell; 2011.

3. Bowe A. MSM and Healthy Hooves. Horses and people.:53-59.

4. Geor RJ. Current concepts on the pathophysiology of pasture-associated laminitis. Vet Clin North Am - Equine Pract. 2010;26(2):265-276. doi:10.1016/j.cveq.2010.06.001

5. Remco Sikkel, Hoefbevangenheid begrijpen, genezen, voorkomen

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