By: Sam Potter (BSc(Hons), MPhilVSc (Equine Nutrition)

Resplendent though it is with butterflies, baby birds and long-awaited warm weather, spring can seem more than a little daunting if you own a horse who is prone to laminitis (we know exactly what this feels like). Spring can catch you unawares… You don’t implement management strategies soon enough and before you know it – after a few sunny spring days – laminitis strikes. Then follows the whole stressful saga of locking your horse off pasture and feeding hay (and googling everything ever written about managing laminitic horses).

But what if you could manage your horse on pasture AND avoid laminitis (and a lot of worry in the process)? It is actually possible and the key is using tools which help you limit how much pasture your laminitis-prone horse eats during Spring.

What causes pasture-associated laminitis in horses?

‘Pasture-associated laminitis’ refers to laminitis that occurs in horses who are grazing pasture.

Horses who experience this type of laminitis secrete higher than normal levels of insulin in response to the sugar and starch they consume in the pasture.

Insulin is a hormone whose main function is to control blood glucose levels. Just like in humans, when your horse eats something high in sugar or starch, their blood glucose levels go up. Their body then secretes insulin, to take up the glucose and store it away in the fat cells and liver.

Compared with normal horses, horses predisposed to laminitis tend to secrete much more insulin in response to rises in blood glucose. But unfortunately for horses, high levels of circulating insulin can cause laminitis through weakening of the hoof laminae tissue and changes in blood flow within the hoof structure.

Definitely not what you want.

It is believed that these horses are probably genetically predisposed to have higher insulin responses. Breeds considered most at risk include most pony breeds, Andalusians, Morgan horses, Quarter horses, Arabians and Warmbloods.

What makes Spring a high-risk time for laminitis?

With spring comes warmth. The sun shines and the soil warms up – in short, ideal conditions for super-charged grass growth.

Cast your mind back to science lessons at school and you’ll recall that during the process of photosynthesis, plants (including grass) use sunshine plus water plus carbon dioxide to produce sugar and starch – which they use to fuel their own growth. It’s one of nature’s magic tricks, but it means when it’s sunny, the amount of sugar and starch in grass gradually increases throughout the day. Then, once the sun goes down, the grass uses some of the sugar and starch for growth and stores the rest at its base for a rainy day (literally).

This means that the levels of sugar and starch present in grass are lowest in the early hours of the morning (before the grass has had a chance to photosynthesize). But there are times during spring when some grasses will always have high sugar and starch levels – literally all day – so they will be unsafe for laminitis-prone horses 24/7.

However, not all grasses are problematic for laminitis-prone horses. Grasses that are commonly found in Southern Australia and New Zealand (C3 grasses) are often at the highest risk of containing large amounts of sugars. These include ryegrasses, phalaris, cocksfoot, tall fescue and brome grasses and some cereals like oats, barley and wheat.

Subtropical and native grasses (C4 grasses) are often the safest, as they tend not to accumulate large amounts of sugar or starch. These include couch, kikuyu, rhodes grass, digit grass, panic grass and native grasses like spear grass, wallaby grass, mitchell grass, bluegrass, red grass or weeping grass.

Why is pasture such a problem?

For many horses, pasture constitutes almost all of their diet. A 300kg pony might consume 40-60kg of pasture per day. This can add up to a really big daily sugar intake and because horses at pasture graze for around 16 hours/day, all that sugary pasture causes a sustained increase in blood glucose and insulin for much of the day.

Is short or tall pasture safer for laminitis-prone horses?

Firstly, any horse that has active laminitis or is recovering from a recent bout of laminitis should NOT have access to any form of pasture – pasture height is irrelevant in this case. They just can’t have it.

But when we’re talking about prevention…

Pasture that is under 5cm high is classified as short and it can be especially problematic for laminitis-prone horses. This is because grass tends to store sugar and starch in the lower section of its stem, and hence short grass can have a higher concentration of sugars. While your horse may not be able to physically consume large volumes of short pasture, it can still be dangerous because the concentration of sugar is so much greater. Grazing pastures that are short also stresses the plant, which triggers even greater sugar production for increased growth (which is bad for both your laminitis-prone horse AND the grass).

Taller pasture – 15-20cm or greater in height – can often be lower in sugars compared to short pasture. The obvious downside though, is that horses can normally eat a whole lot more taller pasture each day, which can also result in them consuming quite a lot of sugar.

So there’s no one perfect answer. However, taller pasture is likely to be safer for your laminitis-prone horse, but the amount your horse eats of it should be limited. How do you do that?

How to limit your horse's pasture intake

Limiting pasture intake is the best management strategy you can use to minimise the risk of laminitis in horses grazing pasture in Spring. All 3 tools we’re about to look at can effectively limit pasture intake – what method you choose will depend on your facilities and your individual horse.

      1. Strip grazing

Strip grazing involves fencing off a small strip (10-20 m wide) in your horse’s pasture using a portable electric fence. The fence is moved daily to allocate a fresh strip of pasture to graze. Ideally a lead (front) fence and a back fence are used to prevent horses having access to the previously grazed strips (which also has the benefit of allowing your pasture to ‘rest’ and regrow before the next grazing).

Pros:

• Strip grazing has been shown to reduce intake of pasture by 20-30% compared to ponies with 24/7 access to pasture (Longland et al, 2020)
• Horses will tend to eat the bulk of the allocated pasture in a shorter period ie. within a couple of hours each morning when sugar content is likely to be lowest
• Low NSC hay can be provided in addition to allocated pasture to ensure adequate forage intake
• Horses can exercise and socialise freely
• An excellent pasture management tool to prevent overgrazing and improve soil health

Cons:

• There are some initial setup costs with portable electric fencing
• Need to consider a portable water source
• Can be time consuming to move fences daily

      2. Grazing muzzles

Pros:

• Grazing muzzles can restrict pasture intake by up to 80%!
• Horses can exercise and socialise freely
• Prevents overgrazing of pasture and limits the horse’s ability to eat the part of the plant that is often highest in starch and sugar – the lowest part

Cons:

• Horses need to be adapted to wearing a muzzle to be sure they are eating and drinking through the muzzle before being turned out for prolonged periods wearing the muzzle
• There is some anecdotal evidence of increased incisor teeth wear in muzzled horses
• Incorrectly or poor fitting muzzles can rub and cause discomfort
• Pasture height is important. Pasture that is too short or too tall can result in frustration and horses not being able to eat enough pasture each day to meet forage requirements to avoid risk of gastric ulcers and colic
• Pasture that is too short (<2.5 cm in height) the leaves don’t reach through the muzzle for the horses to effectively graze
• Pasture that is too tall (> 20cm in height) results in the grass leaves folding over rather than coming up through the holes in the muzzle
• Horses can’t eat supplementary hay that is provided while muzzled therefore forage intake must be adequate from pasture alone or time off pasture without the muzzle is necessary to feed supplementary hay

      3. Restricting grazing time

This works on the concept of grazing pasture for short periods when it is hopefully at its lowest starch and sugar levels. Generally, this is the very early hours of the morning and up until 2-3 hours after sunrise. The remainder of the day and night, the horse should be kept in dry yards with access to adequate, low sugar and starch hay.

Pros:

• Horses don’t have access to pasture during periods where starch and sugar levels are at their highest
• No tools or equipment need to be purchased

Cons:

• Some horses can gorge themselves and eat significant amounts of pasture in a short period – more problematic if energy restriction is required to control weight. Use of a grazing muzzle can overcome this.
• Free exercise is reduced as horses spend most of the time in a dry yard.

When to start limiting pasture intake to avoid laminitis?

Implementing management strategies early is the key to avoiding laminitis. There is no set date to start and timing will vary depending on your situation and the season. As a rule of thumb, start limiting your laminitis-prone horse’s pasture intake as soon as daily temperatures start to increase and days become mainly sunny. Also allow time for your horse to adapt to changes in management such as wearing a grazing muzzle or changing from predominantly pasture-based diet to a diet based on hay.

What else can I do for my laminitis-prone horse?

Be prepared! Have a supply of low sugar and starch hay on hand.

This applies to all horse owners but is particularly important if your horse is laminitis-prone. Limiting access to pasture often means that your horse will need extra forage in their diet - predominantly low sugar and starch hay.

And if laminitis does strike, you won’t have the luxury of time – your horse will need to be taken off pasture immediately and have access to an appropriate forage alternative. Low sugar and starch hay can be hard to come by, so having a stockpile of it in the shed is one less thing to worry about when managing a laminitis-prone horse.

Hay which is typically low in sugar and starch include Rhodes grass hay, Teff hay, other warm season grass hays, native grass hay and lucerne hay. Cool season grass hays should be tested to identify suitable options with non-structural carbohydrate (NSC = starch + water-soluble carbohydrates) content of less than 12% (dry matter basis).

Exercise your horse 3-5 times per week

Exercise has been shown to improve insulin sensitivity, which means your horse becomes better at secreting less insulin in response to elevated blood glucose levels. By improving insulin sensitivity, horses are at less risk of laminitic episodes. Low to moderate exercise (trotting and cantering) for 30 minutes 3-5 times per week is recommended. This is only advised for horses that have fully recovered from laminitis and after speaking with your veterinarian.

Support their gut health

A preliminary study has shown differences in faecal microbial populations in horses with Equine Metabolic Syndrome (EMS) compared with non-EMS control horses on the same diet. EMS is the term used to describe horses that demonstrate insulin dysregulation (what we’ve been talking about above), with regional or generalised obesity and history of or predisposition to laminitis. What was interesting about this study was that the EMS horses had a smaller diversity of faecal microbes (ie. not a very wide range of different types of gut microbes). While we don’t know the implications of these differences, it makes us think that gut health may also be playing a role in horses who have large insulin responses and who are laminitis-prone as a result.

We also know that fructans (indigestible sugars found in some grasses) are rapidly fermented in the horse’s hindgut, which can make the hindgut too acidic and upset the microbial balance. This, in combination with the possible underlying differences in microbial diversity shown in EMS type horses, might further increase their risk of laminitis when grazing high sugar pastures. It’s a double whammy.

Whilst restricting pasture intake is step one in reducing the risk of laminitis, we suggest that step two should be supporting good gut health. But how?

A diversity of ‘good’ microbes in the gut (because microbial diversity is what you want), can be encouraged by giving your horse access to a diverse range of forages or fibre sources. Feeding a good quality gut health supplement – such as Digestive EQ – to promote overall gut health is also likely to be beneficial.

A note from the Poseidon Team: This is a great time to try MetaboLize.

MetaboLize® has been clinically shown to quickly improve horses mobility, and reduce fatty lumps and cresty necks. Designed to assist the horse's body to effectively metabolise sugar, MetaboLize® is a useful aid for horses who need to lose weight. You can learn more here.

Summary

Excessively high blood insulin levels – secreted in response to grazing high sugar and starch pastures - is the reason for most cases of laminitis in horses at pasture. During spring, when growing conditions are ideal for grass, some species produce large amounts of sugar and starch, which makes it a high-risk time of year for laminitis.

You can limit how much spring grass (and hence how much sugar and starch) your horse eats, by using tools such as strip grazing, a grazing muzzle or restricting grazing time. These all have the advantage of still allowing some paddock turnout for your horse. Implementing these tools early is key, so that you avoid getting caught out.

Low sugar and starch hay is an important source of alternative forage during the high-risk periods and having a good supply of suitable hay is essential. You can also exercise your horse to improve insulin sensitivity.

Early studies in horses show us that gut health seems to play a role in EMS and predisposition to laminitis. Supporting gut health in combination with managing pasture intake may further reduce the risk of pasture associated laminitis.

Managing grazing, laminitis-prone horses in spring is definitely a journey, but it’s heartening to know that you do have some tools to help!

References
Longland, A.C., Barfoot, C. and Harris, P.A. Strip-grazing: Reduces pony dry matter intakes and changes in bodyweight and morphometrics. Equine Veterinary Journal, 2021, Pages 1– 8.
Elzinga, S.E.., Weese, J.S. and Adams, A.A. Comparison of the Fecal Microbiota in Horses With Equine Metabolic Syndrome and Metabolically Normal Controls Fed a Similar All-Forage Diet. Journal of Equine Veterinary Science, Volume 44, 2016, Pages 9-16.