The proper transition to grass in spring

As soon as the first green shoots appear in the fields, horses can't wait to get at them. And we horse people feel our hearts swell when our darlings make their first dash across springtime pastures and then blissfully bury their heads in the grass. Even with all that joy, however, we should not forget that spring turnout can also have its drawbacks: transitioning to pasture grass too quickly can bring the risk of diarrhoea, colic, or worst case, laminitis. Learn here why this transition should be carried out slowly and how you can start the grazing season right.

When can my horse be turned out?

The grazing season traditionally begins in early May, "when the horse chestnuts bloom". Today, most pasture gates are opened when the grass is 20 to 30 cm high. The grass is quite juicy in this growing stage, and over 75% water. Leafy young grasses have a protein content of up to 35 g per kilogramme. What makes spring grass so tasty for horses is its sugar content: High yielding "performance grasses" contain around 23% sugar at the start of the grazing season. This means that a horse that eats 10 kg of grass consumes 2.3 kg of sugar, putting a strain on the metabolism.

Why must I transition my horse to pasture at all?

Most of our horses spend the winter in grassless paddocks to protect the pasture. In our region, few horse owners can turn their horses out to graze during the winter. This is because rain and weather fluctuations make the earth soft, and horses galloping across a pasture will leave deep divots in the turf.

If there is sufficient pasture for turnout, horses will feed on everything left standing from autumn. They will nibble on undergrowth and matted tufts of grass, eat leaves, and gnaw on tree branches and bark. After February they may find a blade or two of grass, then a few more in March. By the time the grazing season begins they will have had weeks to adjust, and their digestive tracts will be accustomed to pasture grass.

Most horses in this region are given primarily high-fibre hay in winter, and receive concentrate feed as well. These dry feeds must be sufficiently chewed and salivated before they are swallowed. The saliva neutralises the pH value in the digestive tract. The horse's digestive system grows accustomed to this feed over the winter months. When the horse is first turned out to graze in the spring, it will scarf down the juicy new grass without much salivation. If the horse consumes a large amount of pasture grass at once, the digestive tract's pH value sinks and the gut milieu is knocked out of balance. This results in faulty fermentation with gas formation in the gastrointestinal tract, leading to colic, watery stool, and diarrhoea.

The excess protein in the young grass is generally not a problem for healthy horses. But a sudden oversupply of protein can cause abrupt changes to the gut flora, leading to digestion problems like soft, foul smelling faeces, bloating, and diarrhoea.

Protein requirement of a 600 kg horse = 363 g pcdCP*/day
Protein requirement of a 300 kg horse = 216 g pcdCP /day

* [precaecal (before passage through the caecum) digestible crude protein]

If one assumes that 1 kg of spring pasture grass contains up to 35 g crude protein and that upwards of 50 kg can be consumed, this results in considerable excesses which present massive challenges to the liver and kidneys! Excessive protein produces harmful metabolites during digestion – hydrogen sulphide, ammonia, and histamines – which must be broken down in the liver and excreted via the kidneys. If a horse's metabolism is already stressed, it will become susceptible to swelling in the legs, eczema, and allergies. Horses that suffer from liver or kidney ailments must, unfortunately, stay out of pastures altogether.

Going "from nought to sixty" with pasture grazing will have serious consequences on the large intestine. The large intestine is populated with microorganisms that can break down crude fibre from plants with help from fermentation processes. The complex carbohydrates cellulose and pectin are used to produce energy in the form of volatile fatty acids, which enter the blood via the intestinal mucosa. This microbiome (gut flora environment) needs to be fed crude fibre regularly. A sudden switch from hay to pasture grass will kill off the microorganisms in the large intestine, with fatal consequences for the horse's metabolism.

How does young grass cause laminitis in horses?

It wasn't all that long ago that laminitis was thought to be caused by the high protein content of spring pastures. Grass was cut short, or susceptible horses were only allowed on areas that had already been grazed.

Today it is believed that the grass's fructans, the substances which store sugar, are responsible for causing laminitis. Fructans are water-soluble sugar molecules that are stored in the plant when there is an energy surplus, in order to then make use of them for growth. A grass's fructan content varies greatly depending on its type, the weather, temperature, and time of day. High and low temperatures mean stress for the plant, temporarily stagnating growth and causing a build-up of fructans. Peak values are measured in spring when the sun is shining but the temperature is too low to facilitate plant growth. Nights in spring are often still quite cold, with the temperature rising significantly in the morning. Consequently, it's not until later in the day that the fructan stores are broken down and fructan levels drop again. It was for this reason that stable masters of old warned against letting the horses out to pasture on frosty spring mornings: although they knew nothing about fructans, they were well able to observe that some horses would contract laminitis.

Contrary to what is often assumed, fructan itself is not harmful to horses. Wild horses have no problems grazing on high-fructan grass. Moreover, the sugar content of the lean steppe grasses on which the wild horses feed is less than 4%, with grasslands drying early in the year to offer little more than "hay on a stalk". But the digestive systems of our well-fed domestic horses are often strained by our feeding practices, and when they ingest the high amounts of fructan in high-sugar grasses, tragedy occurs: If the horse is fed silage, haylage, or high amounts of concentrate feed, the fructan will cause the lactic acid bacteria entering the digestive system to multiply rapidly. However, the horse's large intestine cannot break down lactic acid – it was not designed to, as its ancestors had virtually no lactic acid bacteria in their intestines. A hyperacidity of the chyme occurs, the pH value in the gastrointestinal tract falls, and the "good" gut bacteria die off in large numbers. The released endotoxins pass through the intestinal wall into the bloodstream and into the capillaries of the hoof corium where they trigger inflammation. Horses that are overweight or that suffer from metabolic disorders like Cushing's and EMS are especially susceptible.

Recent studies suggest that a combination of several unfavourable factors must occur to cause an episode of laminitis. Endophytes, for example – moulds that have been "bred into" high-performance grasses to make them particularly hardy – increase the risk of laminitis.

A still-unexplained occurrence is that of equine atypical myopathy. This disease, almost always fatal for the affected horse, is still very rare in our regions. The disease is presumably caused by a soil bacterium that releases toxins especially in spring and autumn after frosty nights with high humidity. Even horses that are let out to pasture for a few hours at a time can contract it.

How can I prevent problems during the transition period?

Take it slow!

Horses can be turned out for short times in February and March, ground conditions permitting, to avoid "forage shock" in April and May. If your horse is greedily eyeing the first blades of grass, it's fine to let him graze for a few minutes in hand. A little bit of grass nibbling in the early months of the year is in any case better than a serious problem at the start of the grazing season. Some horses will eat more grass in a half hour than they did in three hours grazing on winter pastures!

The often-heard solution of extending the horse's turnout by ten minutes each day isn't feasible for larger yards. When the last of 30 horses is let out to pasture, the first must be brought back inside! But perhaps a small, not-too-overgrown patch of grass can be found which can be enclosed with a mobile fence to get the horses accustomed to pasture grass slowly.

Private horse owners will find a gradual lengthening of pasture times easier to implement. Ideally, allow the horses to graze for ten minutes after they've frolicked a bit – which they are sure to do. The best time of day for this is the afternoon, when the grass's fructan content has fallen. The next day, allow them 20 minutes, continuing to lengthen their turnout in this way. Slow adjustment time is key when transitioning to grass. After four to six weeks, the horses can be stay out continually.

Important tip: Don't turn out the herd on a very large pasture! It may well be that even your most obedient horse will have no interest in returning to the barn! A small area defined by mobile fencing will do the trick.

Timely monitoring of the paddock fencing will also save you much trouble. Once the horses get a whiff of the pasture air, they'll test the electric fence in the run and take down boards with skill or brute force. Particularly resourceful horses will also find ways to sneak under the fence or unlatch the gate. Uncontrolled feasting on spring pastures can have negative consequences.

Feed your horse adequate hay

Important: before turnout, feed your horses adequate hay so that they don't gorge themselves on young grass. Hay also acts as a buffer for high-energy forage and keeps the digestive system's pH levels stable. Extra portions of hay can also help a horse suffering from watery stool, bloating, or diarrhoea at the beginning of the grazing season. It is not uncommon for a horse to have watery stools when switching from dry hay to juicy forage. However, consult your vet if the horse's condition does not improve or persists for longer than six weeks despite extra portions of hay!

Caution: it's important that you keep an eye on your horse's weight! Overweight horses can be given hay rations that are 1/3 straw.

Concentrate feed should not be given until after turnout. Spring turnout is the time when minerals should be added, as young grass contains little calcium and magnesium.

Grazing muzzles – yes or no?

There are certainly advantages to muzzles: horses can stay out longer, the herd need not be separated according to weight, horses with sensitive metabolisms can enjoy turnout, no one must stay back in the barn, pawing and feeding from the manger alone. Some horses benefit well from "food brakes". For others, wearing a grazing muzzle is simply stressful, even when everything is done to help them get used to it. Grazing muzzles impede social interactions like grooming and hierarchy behaviours, and conceal the facial expressions of "masked" colleagues. If the horse has real problems wearing a muzzle and falls into deep resignation, it must be decided individually whether the muzzle isn't doing more harm – from stress and frustration – than good.

Caution: some of the "flowerpot with hole" varieties can slip easily. If the muzzle slides out of its correct position, the horse may not be able to eat at all. Make sure the muzzle sits properly to avoid frustration!

Reduce stress

Not just young grass in excess, but also turnout itself can stress a horse's stomach. The new, unfamiliar environment and a newly formed group can raise a horse's stress levels significantly. Fights for dominance and chases also pose a high risk of injury in large pasture areas.

How long may my horse stay turned out after transitioning to pasture?

Extending the grazing period in spring will depend on the vegetation in the pasture and the individual horse. A frequently cited study found that horses are able to anticipate the time they are allowed to spend at pasture, and adapt how quickly they eat accordingly. Horses with severely limited pasture time can eat four times as much grass in one hour as those turned out 24/7 will eat in four hours! Determining whether the grazing period should be extended after the transition will require close observation.

One thing should always be kept in mind, however, and that's the value of turnout. Horses are designed to move about slowly whilst continuously grazing. Tendon problems and gastric ulcers often heal themselves in turned-out horses, and their stress levels sink. The pasture approximates the horse's natural habitat. It is up to us to make our horses' transition from stable to pasture as smooth and enjoyable as possible!  

How can I support my horse's digestion during the transition to grass?

The change in feed and any stress experienced at pasture will put strain on the horse's digestive system. During this transition, stomach ailments that may arise from the transition to pasture can be treated with herbs that have a protective and calming effect on the stomach mucosa.  Liquorice and marsh-mallow contain mucilaginous substances that help an irritated stomach lining. Camomile is anti-inflammatory and analgesic. Fennel promotes peristalsis in the gastrointestinal tract and helps to relieve bloating.

A stable gut microbiome helps the horse adapt to feed changes more easily and protects the horse at pasture from "side effects" of transitioning to grass! A healthy intestinal environment can be supported through herbs containing bitter substances and tannins. The bitter substances in yarrow increase the production of saliva and gastric juices and inhibit the growth of harmful bacteria. Oak bark contains high amounts of tannins which regulate the gut, have astringent effects, and can help relieve diarrhoea and watery stool. Feeding linseed and brewer's yeast has proven effective for diarrhoea: linseeds bind the liquid in the large intestine and slow down the passage of faeces. Brewer's yeast supports and regulates the natural function of the digestive system.

Long-term preventive feeding of herbs such as stinging nettle can reduce the strain to the metabolism caused by the transition to pasture. "Kidney herbs" increase the amount of urine, flush the kidneys, and accelerate detoxification. Plant components that protect the liver, like milk thistle seeds, improve the organ's ability to regenerate and strengthen the liver cells to inhibit the penetration of toxins.

Sources and further reading

• Coenen, M., & Vervuert, I. (2020). Pferdefütterung (6. Ausg.). Stuttgart: Georg Theme Verlag KG.
• Fritz, C. (2002). Pferde fit füttern. München.
• Fritz, C. (Dezember 2020). Tipps für einen optimalen Start in die Weidesaison. Von Pferdegewieher.com: https://pferdegewieher.com/podcast8 abgerufen
• Hecker, B. (Dezember 2020). Opti-Ration. Von https://opti-ration.de/rationsberechnung-fuer-die-fuetterung-in-der-weidezeit/ abgerufen