Grazing muzzles are a staple in the tack room of many pony and horse owners. These muzzles fit over the mouth and nose of a horse and restrict grass intake while allowing access to pasture.
Grazing muzzles have been shown to reduce dry matter intake by between 30 – 80%.  These devices can help prevent laminitis and obesity in horses or ponies by decreasing calorie and sugar intake.
If your horse is over-conditioned and needs to lose weight, using a muzzle while on pasture will help you manage your horse’s weight without needing to isolate them to a stall or dry lot. 
Grazing muzzles allow the horse to be turned out in a herd, enabling social interaction and providing more space to move around. These devices are safe when used properly and have not been shown to cause psychological or physiological stress in horses or ponies.
Why Use A Grazing Muzzle?
The image of a horse spending all day grazing on a lush, green pasture may seem idyllic but, in reality, those lush grasses could seriously harm your horse.
Horses evolved as efficient grazing animals, capable of deriving all the energy they need from relatively poor-quality pastures. But the pastures used for grazing horses in domestic management settings tend to contain improved grass species with significantly higher nutrient density.
Lush pastures or paddocks contain high levels of nonstructural carbohydrates (NSCs), consisting of simple sugars, starch and fructans.
If your horse has unrestricted access to high-quality pasture, they could end up consuming too much sugar, contributing to a number of health problems including weight gain, metabolic syndrome and laminitis.
This is particularly problematic in the spring and summer when horses naturally have a higher appetite. Horses respond to the increased length of daylight by eating more in preparation for decreased availability in winter. 
Although free-choice access to pasture can be a health risk for many horses and ponies, turnout onto pasture has several benefits, including the ability to express foraging behaviours and socialization.
Fitting your horse with a grazing muzzle lets you give your horse freedom of movement and contact with their social group without letting them consume unhealthy amounts of sugar.
A grazing muzzle slows down the rate at which your horse can consume grass. You should also consider good pasture-management techniques to keep your horses safe while turned out on grass.
Carbohydrates in Grasses
How do you know whether your pasture is safe for your horse to graze on or whether a grazing muzzle is necessary?
Some horses can tolerate a higher level of carbohydrates in their grass, whereas others such as those with metabolic issues, may need to avoid all but the lowest quality pastures.
- Stress conditions such as overgrazing and frost
- Time of day
- Time of year
- Plant maturity
- Fertilization practices
The only way to determine the sugar content of your pasture is to take a grass sample and submit it for analysis.
Pasture samples should be frozen until analysis to avoid fermentation, which can lower the sugar level and lead to an inaccurate test result.
Note that there can be significant variation in sugar levels between samples taken from the same field. Submitting multiple samples can increase the reliability of the results.
Consult with a nutritionist for help with interpreting the results of your grass analysis.
Preventing Weight Gain
For metabolically healthy horses, lush pasture can be a rich source of protein and energy. Carefully managed turnout on pasture can support healthy weight gain in under-conditioned horses following potential weight loss during winter.
However, excess weight gain is possible with free-choice access to lush pasture. Horses can consume 1.6-3.2% of their body weight in grass over a 24-hour period, supplying a lot of calories and sugar. 
On a mixed pasture providing 20% crude protein and 2.5 Mcal/kg digestible energy, a 500 kg (1100 lb) horse at maintenance could obtain 150% of their daily energy requirement and over 300% of their required protein intake. 
Over-consumption of pasture can quickly lead to weight gain and increase the risk for metabolic dysfunction. Especially for easy keepers or horses with insulin resistance, rapid weight gain can predispose the horse to equine metabolic syndrome and laminitis.
Grazing muzzles help to restrict calorie intake by reducing forage consumption by 30% on average for horses grazing on different types of grasses.  This can prevent weight gain in healthy horses and help to maintain an appropriate body condition.
Laminitis is a major concern with ponies or overweight horses grazing on lush pasture. This painful inflammatory condition is one of the leading causes of euthanasia in horses.
Laminitis causes swelling of the sensitive hoof laminae, which support the coffin bone. In severe cases, the coffin bone can sink and/or rotate leading to grass founder.
While the exact cause of pasture-associated laminitis continues to be investigated, it is known that high insulin levels (hyperinsulinemia) contribute to the pathology. In most cases, laminitis can be prevented with dietary changes and the restriction of high-NSC forages. 
Horses at risk of laminitis should be turned out with a grazing muzzle during periods of the day when the sugar content in grass is lowest, usually the early morning hours. Turnout on a dry lot with appropriately selected hay or straw may also be recommended to reduce the risk of a laminitic emergency.
Obesity and Insulin Resistance
- Exercise intolerance
- Poor heat tolerance
- Increase in visceral fat (surrounding organs)
- Joint pain and orthopedic issues
- Unsoundness due to increased weight-bearing on their limbs
- Reproductive issues
- Respiratory and cardiovascular problems
Additionally, the increased fat accumulation can make a horse susceptible to insulin resistance. Horses with insulin resistance are more likely to develop laminitis and other metabolic complications, including hyperlipidemia and liver dysfunction. 
Insulin is a hormone released by the pancreas to regulate blood sugar (glucose) levels and transport glucose into cells. When a horse consumes soluble carbohydrates, blood sugar spikes and more insulin is released to promote uptake of sugar into cells.
Insulin-resistant horses are not as sensitive to the effects of this hormone, causing the pancreas to secrete more insulin. When blood sugar levels are elevated in IR horses, they are slow to return to baseline. 
Emaciated horses need to be re-introduced to forage and feed gradually to avoid potentially fatal consequences. Grazing muzzles slow down pasture consumption and prevent the horse from gorging.
Refeeding syndrome occurs when emaciated horses suddenly consume high levels of nutrients, such as carbohydrates, resulting in metabolic and electrolyte imbalances.
A sudden influx of carbohydrates causes insulin to spike, moving blood sugar into cells. Insulin also moves electrolyte minerals including magnesium, calcium, phosphorus and potassium out of the bloodstream and into the cells.
Grazing muzzles allow the emaciated horse to consume the carbohydrates required for weight gain while potentially reducing the risk of refeeding syndrome.
How Do Grazing Muzzles Work?
Research studies show that wearing a grazing muzzle extends foraging time, reduces bite size and decreases overall forage intake when used correctly. 
These muzzles fit comfortably over the nose and mouth of a horse or pony, leaving holes for air circulation to allow for breathing. These holes allow only the tips of grass and forage to poke through, requiring the horse to take small bites.
In a crossover study involving seven horses, researchers from the University of Minnesota found that muzzle horses had 30% lower forage consumption compared to their normal intake. The average reduction in intake was not affected by the type of grass being grazed on. 
In a UK study of four ponies, wearing a muzzle for three hours reduced pasture intake between 75-88% compared to unmuzzled ponies. 
Benefits of Grazing Muzzles
As a method of restricting feed intake, grazing muzzles have a number of benefits.
Grazing muzzles enable horses to be turned out into a natural environment and to graze in larger areas. This promotes the expression of species-appropriate foraging behaviour, supports socialization, and encourages exercise.
Turning out horses on a dry lot and rationing forage can also help to restrict feed intake. However, these methods can result in long periods between meals, which can contribute to gastric ulcers and other digestive problems.
Grazing muzzles extend the amount of time spent feeding. This means your horse will spend less of the day with an empty stomach, reducing the risk of ulceration.
Weight Loss Results
Research shows that grazing muzzles worn continuously during the day can support weight loss. In two studies of miniature horses, wearing a muzzle for 24 hours a day was shown to result in lower body weight after three weeks. 
Weight gain can still occur in horses wearing a muzzle for part of the day because the horse compensates by eating higher amounts of pasture and other feeds when the muzzle is off. 
This suggests that to facilitate weight loss, muzzles should be worn whenever the horse has access to pasture. Equine behaviourists generally recommend limiting muzzle wearing to a maximum of 12 hours per day.
You may need to turn your horse out onto a dry lot with an appropriately selected low-NSC forage when not wearing a muzzle to prevent weight gain.
Not all animals lose weight while wearing a muzzle. In one study, a muzzled pony experienced weight gain at the same rate as unmuzzled ponies. 
Monitor your horse closely for changes in body composition. If your horse is not losing weight, other strategies can be implemented to promote weight loss.
Types of Grazing Muzzles
There are two main types of grazing muzzles used today: nylon web muzzles and plastic basket muzzles.
Nylon Web Muzzles
Nylon web muzzles are made from a strong fabric material woven into an adjustable, loose basket structure. These muzzles are the most common and are inexpensive.
These muzzles can come pre-attached to a halter that fits onto the horse’s head or as a separate basket that can be attached to the horse’s current halter. Usually, these grazing muzzles will come with fleece padding around the nose to prevent rubs.
Nylon web muzzles provide multiple holes for grass to poke through and are pliable enough not to bruise the horse if they happen to hit against a solid object.
Plastic Basket Muzzles
Plastic basket muzzles (such as the Shires GreenGuard Muzzle) are made of a hard, durable plastic and fit over the nose of the horse.
These moulded muzzles attach to the horse’s pre-existing halter and have open spaces for grass to fit through.
Plastic muzzles may outlast fabric models, but the downside is that the material is stiff and not as adjustable. Some horse owners report that these muzzles can cause rubbing and hair loss.
Are Grazing Muzzles Safe?
Studies show that grazing muzzles are generally safe, well-tolerated and do not cause psychological stress for the horse. There are some risks to be aware of, but when used properly the risk is low.
- Muzzled for 10 hours per day
- Muzzled for 24 hours per day
The horses were assessed in each study conditions for 21 days at a time and were observed for changes in behaviour, exercise and stress levels.
Saliva cortisol levels and heart rate were monitored as indicators of physiological stress. Signs of psychological stress were also assessed, including head-shaking, pawing, and rubbing the face to remove the muzzle.
Both of the muzzle conditions resulted in increased stress behaviours for the first day, but these behaviours quickly resolved as the horses became accustomed to the muzzles. No signs of physiological stress were observed during any of the study conditions. 
In another study of muzzled ponies, no abnormal behaviours were noted in ponies wearing the muzzles. 
Risks of Grazing Muzzles
Grazing muzzles are generally safe, but they can pose risks – particularly if the muzzle is not fitted properly or if the wrong muzzle is used.
Some potential adverse effects and ways to mitigate the risks are discussed below.
Risk of Hanging Up
One major risk of putting a grazing muzzle on your horse is the potential for hanging up. The muzzle may get caught on solid objects, such as on low-hanging tree branches, nails on fence posts, other environmental hazards, or even on other horses.
Many horses will panic when caught on something, potentially leading to a serious injury. This is why some horse experts suggest never turning horses out wearing halters. However, grazing muzzles require a halter to be worn to secure the muzzle to your horse’s face.
You can reduce the risk of injury by clearing your horse’s paddock of any unnecessary items that the muzzle could get hung up on. Also, use a leather or breakaway halter that will rip away if caught on an object.
Risk of Tooth Wear
Long-term use of grazing muzzles could contribute to accelerated wear and tear on your horse’s teeth, potentially resulting in dental issues.
Tooth wear occurs when the teeth press and scrape against the muzzle as the horse tries to ingest as much grass as possible. Although there is limited research data on the effects of muzzling and tooth wear, anecdotal evidence suggests a risk of incisor wear.
Many factors can affect the degree of tooth wear that occurs while wearing a grazing muzzle.
- The material of the muzzle: Stiff materials – such as plastic and molded kevlar – are more likely to damage teeth.
- The horse’s tooth health: Horses that have abnormally shaped or especially fragile teeth will experience faster tooth wear.
- The length of grass: Short grass is difficult for horses to grab through the muzzle, but very long grass can fold over and be difficult to pull through the muzzle holes. Mid-length grass pokes through the muzzle’s holes and is the easiest for the horse’s teeth to grab without needing to press down too hard.
- The number of holes: Muzzles with one or two holes may cause frustration, making the horse press down firmly with their teeth to grab more grass. Muzzles with many small holes allow more blades of grass to poke through while still restricting feed intake and reducing frustration.
Equine behaviourists suggest trying multiple muzzles to find the best fit for your horse. Ensure your horse’s teeth are regularly inspected and switch muzzles if tooth damage is apparent. 
Although dental wear is an unfortunate risk with grazing muzzles, most horse owners agree that the risk is worth it to prevent potentially debilitating conditions including colic, laminitis, and insulin resistance.
How to Fit a Muzzle
Fitting a grazing muzzle properly is crucial to reducing the associated risks. Most manufacturers provide a sizing chart to ensure you are purchasing the appropriate fit of muzzle for your horse.
Follow these steps to safely fit your horse with a grazing muzzle:
- Refer to the sizing chart for the specific brand of grazing muzzle you are purchasing. Most horses wear the same size muzzle as a halter, but there can be variation in sizing between different muzzle fits. After choosing a style and size, note the depth and circumference of the muzzle.
- Confirm the depth of muzzle required with a measuring tape. Stand to your horse’s side, looking at the profile of their head. Place the start of your measuring tape one inch lower than the tip of their lips and measure up towards their ears. Compare this value to the depth of the muzzle size you have chosen.
- Confirm the circumference size required by measuring around your horse’s muzzle two inches above the nose, keeping the tape snug. Add two inches to this measurement to accommodate for chewing.
- If the horse is in between sizes, choose the larger size to allow more room for jaw movement.
When putting the muzzle on your horse for the first time, make sure it is sitting one inch below the tip of their lips. This will promote comfort and provide adequate room for lip and tongue movement.
A small muzzle can restrict the horse’s chewing and lead to digestive issues and increased dental wear. You should be able to insert 3 or 4 fingers into the space between the hose’s face and the rim of the muzzle to ensure total freedom of movement of their jaw. 
Tips for Using Grazing Muzzles
To avoid frustration, introduce the grazing muzzle in short durations. Start with a period of 1-2 hours and gradually increase from there to an entire grazing period. 
Monitor your horse or pony closely after introducing a grazing muzzle to ensure it is well-tolerated and your horse is not displaying abnormal behaviours.
Clean the muzzle regularly and check it for damage. Observe your horse for any signs of skin irritation or rubbing where the muzzle attaches.
Keep a weekly log of your horse’s body condition score to ensure their weight is being properly managed. A rapid decline in bodyweight could indicate your horse is not getting enough calories and may lead to hyperlipidemia.
Some horses will still gain weight when wearing a muzzle. In these cases, you may need to restrict turnout time or turn your horse out into a dry or sparse lot to reduce calorie intake.
Make sure your horse cannot get out of their muzzle. If the muzzle falls off while your horse is unsupervised, it could gorge itself on pasture and cause a laminitic emergency.
Horses that require restricted forage intake still have the same requirements for vitamins and minerals. Feeding a concentrated vitamin and mineral supplement is essential to meeting nutrient requirements without adding calories to the diet.
If you have a horse or pony that is obese or prone to metabolic issues, work with an equine nutritionist to ensure their diet is fully balanced and is optimized for weight management. Submit your horse’s information online for a free evaluation and feeding plan.
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