Pasture Laminitis

Grazing on grass, especially in spring/summer can be a major problem for some horses, from catastrophic life threatening laminitis to lower grade separation. What does ‘pasture laminitis’ mean?

When we gaze out the window at our horses playing and grazing together in spring (or winter) on plenty of grass we may feel pleased to see our horses doing so well. Yet appearances may be deceiving and down the track we may find our horse’s hooves showing clear signs of separation and tenderness.

On top of the separation, there may be abscesses and seedy toe. The question comes to mind, why is it more likely in spring (or winter)?

Grass is by far the best feed for horses, with the largest range of nutrients. Not one product, in a bag or container can compete. Horses evolved on a fairly continuous intake of low fat and high fibre forage. Fibre is essential for healthy functioning of the digestive tract, it is not surprising to find horses on high grain/low fibre diets with hours between feeds are more likely to suffer from colic, ulcers and digestive upsets. All horses, even those on very heavy workloads need as much fibre in their diet as possible, and grass is an excellent source of protein, minerals and vitamins. All grass species, regardless of the quality of the soil they are grown in contain varying levels of these nutrients, without those nutrients the plants wouldn’t be able to function and survive.

The ideal, able to eat grass and not be laminitic prone

Though grass (and hay) is a nutritious feed it can also be a health hazard to some horses, especially  pasture improved species of grass developed to maximise growth rates in cattle. In spring, warmer temperatures and cooler nights produce a lot of new growth, timed beautifully for the higher needs of pregnant and lactating mares. This new growth can be very high in easily digestible carbohydrates called sugars and starch which in some horses, will cause insulin to rise. These horses are metabolically insulin resistant (IR), or due to high levels of gut incretins produced, have high insulin. It’s the high levels of insulin that can cause laminitis in these horses with theses metabolic conditions. The first sign of a horse not dealing well with a high sugar + starch intake can be low grade laminitis. Dr Eleanor Kellon VMD and the Equine Cushings and Insulin Resistance group, ECIR recommend sugar (ESC) + starch to be under 10%.

Low grade laminitis, as the name suggests, is a mild form of laminitis where the horse shows little of the symptoms associated with laminitis and is far more common than many horse owners realise. Often the horse owner is unaware of any episodes of lower grade laminitis yet the typical changes are there in the feet. If the cause is not removed then initially the horse may not show a lot of pain or discomfort in the hooves yet the hooves may undergo the following changes:

  • Horizontal ridges (rings) on the exterior of the hoof

  • Inflammation and eventual separation of the laminae or leaf like folds in which the pedal bone is normally suspended leads to a separation of the hoof wall from the hoof. This is seen as a widening of the laminae particularly at the toe and has the effect of making the horse more susceptible to hoof abscesses.

  • Rather than standing normally the horse will shift his weight from one foot to the other. If the hind limbs are more affected, the horse will stand with its front limbs back underneath to take more weight.

  • Demonstrate a reluctance to step out when ridden.

  • Reluctance to pick up feet.

  • In time the laminitis could develop to tenderness on any surface with a strong ‘bounding’ pulse to the feet indicating increased blood flow and inflammation (heat) of the area. This chronic laminitis may then develop further with pedal bone rotation and solar penetration, known as ‘founder’.

Dietary laminitis is a very complex condition, and the likelihood of any particular horse getting it from excessive sugar and starch in the diet is influenced by numerous factors:

  • Seasonal variation, with early spring grass being the big risk. New shoots of grass are higher in sugar + starch.

  • Type of grass – legumes such as clover and lucerne being particularly rich.

  • Grass stressed from drought or frost is higher in sugar and starch. Cold overnight temperatures can mean that the grass is very high in sugar + starch first thing in the morning.

  • Horses that have had previous laminar disease (whether from laminitis, puncture wounds or severe sole abscesses) seem more susceptible to subsequent bouts of laminitis.

  • Overweight IR horses can have a higher predisposition to laminitis.

  • A horse in regular work is less likely to be affected.

What actually causes the separation of the laminae that support the pedal bond is under investigation. A RIRDC study showed that high levels of the hormone insulin triggers lamellar separation. Carbohydrates like sugar and starch are broken down into glucose. As glucose rises in the blood, the pancreas secretes insulin in response to the increased glucose. Insulin enables glucose to move from the blood into cells. A large and prolonged influx of sugar and starch will cause a large and prolonged rise in insulin and this has been demonstrated to trigger separation of the lamellae in the hooves though the actual mechanism is still unknown.

Sugar and starch are broken down in the stomach and throughout the length of the small intestine but if a significant amount makes it to the large intestine then the delicate balance of bacteria can be upset. The large intestine becomes more acidic, potentially damaging the intestinal wall so that it becomes ‘leaky’. This acidity may cause many of the fibre fermenting bacteria to die and release toxins that pass into the bloodstream through the breaks in the wall. The toxins are thought to alter the blood circulation within the hooves, or trigger the separation of the lamellae. Another theory suggests that when the intestinal environment changes, bacteria that produces laminitis triggering factors may overwhelm others.

How to manage horses prone to lower grade laminitis

The prevention and rehabilitation of laminitis is all about removing the cause – in this case the source of the excessive sugar and starch in the diet. To minimise the risk, regular exercise is highly effective and can make all the difference between a horse that has to be deprived of pasture and one that can handle the high sugar + starch content. Domesticated horses kept in small paddocks are at far higher risk than non domesticated horses as they would be covering large distances rather than grazing and gorging themselves in a small area with little movement.

Ensure your horse isn’t overweight. It isn’t clear as yet whether it’s the obesity that can reduce a horse’s ability to handle a high level of sugar + starch or the high grain and often high fat diets. At an extreme this can develop into insulin resistance where an inability to respond to insulin occurs. A greater than normal amount of insulin has to be secreted to move glucose into cells, triggering laminitis.

For managing horses on pasture that are susceptible to low grade laminitis it is useful to know when sugars and starch are at their highest. Generally, the safest time for horses to graze is between 3am and 10am in the morning as this is when sugars and starch are at their lowest though this won’t apply if overnight temperatures are very cold. Grass growing in the shade is safer compared to grass in full sunlight and ditto for a cloudy day compared to a day without clouds to obstruct the sun.

If you need to prevent horses from grazing later in the day there are two methods that can be adopted.

One option depending on your property is the implementation of a paddock paradise arrangement. Jaime Jackson, a hoof care practitioner in America published ‘Paddock Paradise, A Guide to Natural Horse Boarding’. The paddock paradise idea is where a laneway is fenced off around the perimeter of a paddock using electric tape or around the perimeter of the whole property. Depending on the insulin resistance of the horses, either the grass may need to be removed or their grazing may limit the grass sufficiently. Never underestimate how efficient a horse can be at nipping at the new growth, even when very short. Low sugar + starch hay could be distributed in the laneway.

Paddock Paradise or laneway system

This would entail some initial effort and expense but it would mean that the horses could graze in paddock in the morning when sugars and starch are at their lowest and then later placed in the laneway for plenty of movement which a small dirt yard cannot provide. An extra benefit is that time in the laneway means the paddocks can be rested. Another benefit is that horses kept in paddock paradise type laneway are reported to move far more than horses in paddocks. Read more about paddock paradise, an Australian example.

Another option is a well fitting and padded grazing muzzle. A muzzle will restrict grass intake late in the day when sugar and starch is highest but still allows drinking and socialising with other horses in the paddock. A little bit of grass can still be eaten in a muzzle. However, ensure the opening is not too small, and isn’t going to damage the teeth surface.

The worst option that cannot be recommended is locking a horse up without feed. It means the horse is prevented from moving and getting exercise, no food can lead to digestive upsets and separation from the rest of the herd is distressing. Horses tend to gorge on grass when released if locked up for a period of time.

Grazing muzzle controls intake

Is slashing a paddock a good idea?

Slashing a paddock or mowing a paddock for hay and allowing a horse to graze the new growth is asking for trouble. The best growth stage for the lowest sugar and starch is when the grass has flowered and seed is spread. If any of the grass stills has seeds this may not present a problem even though the seeds like grains are high in starch but their proportion of the grass biomass is small and soluble carbohydrates in the above ground portion of the grasses drops dramatically after the seeds are set. Unfortunately though, some horses are so sugar sensitive that even the seeds will cause harm. Many insulin resistant horses cannot tolerate any grass, let alone mature grasses.

Ideally, allow the grass to be grazed when mature and once eaten down to about 8 cm move the horses onto another section or paddock of mature grass. If you do need to slash to manage large areas of pasture, larger than what the horses can eat then slash and wait 2 to 3 weeks for the regrowth to reach a height of about 25 cm. The regrowth will use up a lot of the sugar and starch for growth and turn it into protein and fibre. Rotational grazing is the best way to manage your paddocks and sugar sensitive horses who can tolerate some grass. The heights given are a guide only, it will depend on the species of grass.

What about hay?

Hay can also be very high in sugar and starch. Growing conditions, time of day when harvested and stage of growth are most important. Sugars rise through the day on a sunny day, and decrease overnight when nights are warm. Mature stands of grass are safer than young, growing grasses. This means that unstressed mature grass cut early in the morning will be safer than grass harvested late in the day. Drought or nutrient deficient stressed grass will be higher in sugar + starch.

Many people who own horses sensitive to high levels of sugar + starch on predominantly hay diets often like to get their hay analysed at a laboratory to find out how safe the hay is to feed. Soaking hay for up to 30 minutes in hot water, 1 hour in cold water can remove a significant amount of soluble sugar but won’t reduce the starch levels. Dr Eleanor Kellon VMD, an equine nutrition specialist in America was one of the first to be concerned about iron overload as a risk factor for insulin resistance in horses as it is in people; hence any feed or supplements with high levels of iron should be avoided.

Article originally published in the September – October 2009 issue of Equine Excellence magazine with the title of ‘Grass and subclinical laminitis’, updated since.

Further information:

Links may change over time. If a link doesn’t work, search the title in your search engine.

ECIR website

Equine Cushings and Insulin Resistance discussion group. Dr Eleanor Kellon VMD oversees.

Dr Eleanor Kellon VMD

Jaime Jackson (2007) Paddock Paradise, A Guide to Natural Horse Boarding

Professor Chris Pollitt

L. R Turner, D. J Donaghy, P. A Lane and R. P Rawnsley (2007) Distribution of Water-Soluble Carbohydrate Reserves in the Stubble of Prairie Grass and Orchardgrass Plants Agron. J. 99(2):591-594 with Katy Watts

M Sillence, K Asplin, C Pollitt and C McGowan (2007) What Causes Equine Laminitis? RIRDC

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