Most horses are turned out daily on grass pastures or sand paddocks. How long and often horses are turned out depends on the different seasons. During autumn and winter, horses spend more time indoors due to shorter days and worse weather conditions, compared to summer when the weather is better and days are longer. Turning out horses allows them to have social interactions with other horses and gives them the ability to move freely. This is important for the horse's health and well-being. During spring and summer, horses often have access to fresh grass in addition to hay. Grass has different nutritional values in comparison to other types of roughage, therefore it is important to take this into account when horses get access to grass. Managing grass intake avoids dietary imbalances and promotes optimal health and well-being of the horse.
Wild horses graze between 14 and 16 hours per day. The anatomy of the horse's digestive system requires the horse to digest small portions of food frequently 1. It is therefore important for horses to have daily access to sufficient roughage to carry out their natural behaviour. Allowing horses to graze on pasture, during seasons when fresh grass is available, is therefore ideal for performing natural behaviour and providing sufficient roughage. Horses, when provided with unrestricted access to a grass pasture, will graze until no grass is left. Fresh grass contains energy, protein, vitamins and minerals which are important for the body. For example, grass contains a source of Vitamin E which is required for healthy muscles, the immune system and functions as an antioxidant in the body 2. Determining the precise nutritional value of grass is challenging due to various factors, such as weather and growth stage. Unlimited access to grass can therefore lead to an imbalance in the horse's diet 3. Besides, fresh spring grass often contains higher levels of sugars which can affect the horse's health 4. Therefore it is important to regulate the intake of fresh gras when horses are allowed to graze on grass pastures during spring.
Sugar content in Fresh Grass
Grass, through the process of photosynthesis, produces glucose (or sugar) which is used as an energy source for plant growth 5. The process of photosynthesis requires oxygen, water and light. At night, when it is dark and the plant can no longer perform photosynthesis, the grass uses the energy produced during the day to grow, reducing the sugar content in the grass 5. But during spring, nights are often still cold which influences the growth process resulting in the grass retaining water and sugar to survive 5. As a result, the sugar content does not reduce and the grass still contains too much sugar in the morning when the horses are allowed on pasture 5. Especially during spring when horses have access to fresh grass again for the first time, the intake of too much sugar can affect the horse’s health. When the horse has access to (sugar-rich) grass, without regulating the intake and allowing the horse to get used to the spring grass, the horse's diet suddenly changes which can result in health problems such as colic, insulin resistance or laminitis 6.
To keep track of when the grass is high in sugars, the fructan index can be used as a tool. This is an index based on current weather information. It thus provides insight into the sugar content of the grass in your area and can be used as a tool during the grazing season.
Management Systems to Regulate Grass Intake of the Horse
Grass intake can be regulated by reducing the amount of grass available to the horse, limiting the time the horse is on pasture or ensuring that the horse can take in less grass.
To regulate the horse's grass intake, different grazing systems can be implemented 7,8. As indicated earlier, allowing the horse unlimited access to fresh grass is a possibility. But for horses susceptible to laminitis or suffering from other health conditions where high sugar intake should be avoided, this is not ideal and can affect the horse’s health 4. Especially when horses have not been able to graze during winter, unrestricted grazing will not be beneficial as grass contains a higher amount of sugar during spring. A sudden increased intake can cause a range of health issues which should be avoided.
A commonly used method to regulate the grass intake is strip grazing 9. By using a movable fence, grass intake is regulated by replacing the fence making a strip of fresh grass available to the horse 10. The movable fence can either be placed on one side or both sides of the pasture. By placing a fence on one side, the surface of the pasture available to the horse will increase every time the fence is moved. Placing two fences provides the horse with fresh grass but also allows the part that has already been grazed on to ‘rest’ by moving the back fence as well as the fence in front (Figure 1). Research has shown that the use of strip grazing has a positive effect on the Body Condition Score (BCS) and body weight 7,9. In addition, strip grazing causes the horse to ingest significantly less grass compared to when unlimited grass is offered 9. However, studies showed that horses, when given a new strip of fresh grass to graze on, ingested the grass faster than horses that have unlimited access to grass and thus graze more slowly 7,9. A study conducted by Dowler et al. (2012), showed that when horses graze for eight hours, during the first four hours they will ingest more grass in comparison to the second four hours. It's therefore important to consider the time of day when giving horses access to fresh grass, as grass tends to contain more sugar in the morning after cold nights. If horses have access to this sugar-rich grass for the first four hours during the morning, they will still absorb too much sugar. But, when used appropriately, strip grazing is an effective way to control a horse's grass intake leading to better weight management when compared to unrestricted grazing.
Figure 1 Pasture 1 has one movable wire, increasing the area of the pasture each time a new strip of fresh grass is added. Pasture 2 has a movable wire at the front and back, creating 3 strips. The light green strip is the grazed area that can now 'rest', the middle strip is where the horse grazes and a new strip of grass is added each time. The last strip (dark green) is the part that has not yet been grazed.
Another way to regulate grass intake is by limiting their access to pasture and allowing them to graze for shorter periods. However, it is essential for the horse's well-being to have enough daily free exercise. Grazing horses on a grass pasture enables them to move freely. To reduce the amount of grass a horse consumes, it is recommended to alternate between a grass pasture and a paddock where the horse has access to a different type of roughage such as hay. However, research indicates that horses adapt to the routine, leading them to increase consumption of grass in a shorter period 11.
During periods when grass contains high amounts of sugar, it is recommended that horses prone to laminitis or diagnosed with PPID, insulin resistance or EMS do not have access to fresh grass. However, these horses should also be turned out when possible. Instead of turning them out on grass pastures, they can be turned out on sand paddocks where they have access to low-sugar roughage.
If the nights are still cold during spring, it is advised to mow the grass in the morning before the horses are allowed to graze on the pasture. The sugars in the grass are used for grass growth. Mowing the grass stimulates the growth process of new leaves by allowing the stored sugars in the roots to be redistributed throughout the whole plant 12. However, it's important to avoid cutting the grass too short since in the lower portion of the grass most of the sugar is stored, which means that even short grass can still contain a lot of sugar.
Another option, which is used more frequently, is a grazing muzzle. Research conducted by Glunk et al (2014) showed that horses wearing a grazing muzzle ingested 30% less grass than horses without a grazing muzzle during this study. The grazing muzzle allows the horse to take in less grass but still have the opportunity to be on pasture 13. Studies testing grazing muzzles used pastures where the grass was at least 8 cm long and up to 20 cm high 11,13. If the grass is too short, the grass does not reach the mouth of the horse through the muzzle. However, long grass is harder to chew with a grazing muzzle than shorter grass. Some horses will not graze at all when wearing a grazing muzzle or find it difficult to drink water with the grazing muzzle on 14. Therefore, it's important to monitor a horse the first few times when it is wearing a muzzle to make sure they don't go too long without eating or drinking. Besides, the grazing muzzle is not made to be worn throughout the whole day. It can be used temporarily, such as during periods when sugar levels are high. Wearing a muzzle is also a suitable option, for instance, when horses are outside on grass pastures 24 hours a day. However, it is possible that once the muzzle is taken off, the horse will start grazing more rapidly and consume more grass. A grazing muzzle can therefore be combined with another grazing system such as strip grazing, to prevent the horse from ingesting too much sugar once the muzzle is taken off.
It is important to regulate a horse's grass intake during the transition from winter to spring to prevent excessive sugar consumption. Especially when horses have spent a lot of time indoors during the winter and have not yet had access to grass. There are several ways to regulate grass intake. It is important to consider which system can be applied to your horse's management. In addition, the timing of grass access significantly impacts sugar intake in horses. Good management is therefore essential to prevent health problems due to high sugar intake.
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