When Pasture is Too Much of a Good Thing

Also see Sidebar "Fit and Comfort of a Grazing Muzzle" below.

Dr. Tania Cubitt and Dr. Stephen Duren

The horse has evolved as a grazing animal, hence, pasture plays a pivotal role in equine nutrition. Reported intakes of fresh pasture by horses can range from 1.5 to 5.2 percent of body weight per day. With such a large intake of pasture possible, can horses overconsume? What components of pasture grass can cause problems if taken in at excessive levels?

What’s in the grass?

Pasture has been implicated in the onset of several metabolic disorders in horses. During photosynthesis, green plants ‘fix’ atmospheric carbon dioxide in the presence of light, resulting in the production of simple sugars. When sugars are produced in excess of the energy requirement of the plant for growth and development, they are converted into storage, or reserve carbohydrates. These carbohydrates make up the non-structural carbohydrate (NSC) fraction of the plant. These non-structural carbohydrates follow a seasonal pattern with highest values in spring compared to summer and winter, and intermediate values in the autumn. The overconsumption of non-structural carbohydrates by grazing horses have been implicated in disorders including insulin resistance and laminitis.

Excess grass consumption and obesity

In addition to non-structural carbohydrates causing metabolic issues, the sheer overconsumption of pasture grass can cause obesity in horses. Obesity can result in further problems with insulin sensitivity as body fat mass increases. All of these overweight conditions result in a cascade of problems that at the very least leave your horse fat and intolerant of exercise, to far more severe conditions such as insulin insensitivity and laminitis. It has been reported that excessive pasture intake accounts for nearly 50 percent of all reported cases of laminitis. Obesity, therefore must be corrected.

First step is calorie control

The first step in any weight reduction program is calorie control. Elimination of all grain from the diet is a logical step for overweight horses. A low intake vitamin and mineral supplement pellet should be added to the diet as a means of supplying key nutrients to the horse without excess calories. 

Another key to success is limiting or eliminating access to pasture. Pasture grazing represents an unregulated source of calories that cannot be easily quantified. It is therefore necessary to limit pasture access until weight loss has been achieved.

Photo: ©Chelle129-Fotolia.com

How grazing muzzles work

Physical prevention of excessive pasture intake by horses can be achieved using grazing muzzles, which are commonly recommended for controlling grass intake in overweight and laminitis prone horses and ponies. The use of grazing muzzles reduces bite size and restricts intake to the tops of leaves, where the concentrations of sugar (NSC) tend to be lowest. Grazing muzzles may be favoured by owners over other methods of intake restriction that limit animals to very short turnout times or confinement to stables or small bare paddocks. The muzzles enable the animal to graze larger areas and for longer periods, and owners do not have to implement severe changes to their facilities. In addition, a horse that is allowed to graze with a muzzle continues to move around in the pasture and get at least some exercise.

Does my horse or pony need one?

Not all horse owners need to be concerned with pasture intake restriction. For the majority of horses, total restriction is not always a viable or desirable option for financial, welfare, and health reasons. It may also not be necessary for those animals that are not predisposed to a metabolic disorder. The first step in determining if your horse is a candidate for a grazing muzzle is to determine the laminitis risk.

There may be breed, age, and sex influences in the incidence of laminitis. Certainly it is generally accepted that ponies are more commonly affected by laminitis than horses. If you own a pony, buy a grazing muzzle because you will eventually need to use it. Thoroughbreds and Standardbreds have a lower risk of developing laminitis, but this is probably due to activity level rather than breed. Ponies and horses that have previously been affected with laminitis or are affected with certain other diseases (e.g. Cushing’s disease or insulin resistance) are at higher risk of developing laminitis. For those higher risk animals a grazing muzzle may be necessary. A less radical solution compared to using a grazing muzzle would be to restrict pasture access by controlling the amount of time they graze. Simply restrict the grazing opportunity to two hours or less per day. Further, grazing can be restricted during times of high risk, such as during the spring and fall.

When and how to use the muzzle

The pasture is the most dynamic and dangerous component of the diet if the horse has previously suffered from laminitis. If an affected horse is returned to pasture, use of a grazing muzzle is recommended to limit grass intake. Grazing muzzles can be worn every day or only during months when the pasture grass is more abundant and contains higher concentrations of non-structural carbohydrates. Turnout on pasture should be avoided when the pasture grass is growing rapidly in the spring after the weather turns warmer or during the summer after heavy rain. Temperate pasture grasses also accumulate sugar when they are stressed by drought or the onset of winter. When a horse is re-turned to pasture after being confined to a stall for several days, reintroduction should occur gradually, with no more than one hour of grazing at a time for the first two weeks. 

How well does a muzzle work?

While grazing muzzles are recommended to reduce pasture intake, there is limited data on their effectiveness. A recent study utilizing ponies aimed to determine the extent of intake restriction imposed by grazing muzzles. Ponies fitted with grazing muzzles on average ate approximately 83 percent less forage than those without grazing muzzles. Ponies with muzzles were only able to consume 0.14 percent of their body weight during three hours. The study indicates that grazing muzzles appear to be an effective means of restricting pasture intake by ponies. 

Guidelines for use 

• Make sure the muzzle fits correctly as this will help prevent your horse removing it, and check the fit often. The extra weight of the muzzle adds pressure to the bridge of the nose, and pressure sores can sometimes develop. Encasing the noseband in fleece may provide relief. The muzzle should be attached to a breakaway halter.
• Slowly introduce the muzzle by leaving it on for short periods in the stable and reward your horse with a treat through the hole in the muzzle each time you put it on and take it off. As you progress outside with your horse wearing the muzzle, feed grass through the hole so your horse gets the idea that he can still eat. Initially, leave the muzzle on for short periods gradually building up the length of time your horse grazes with the muzzle on.
• Make sure your horse is comfortable drinking with the grazing muzzle on. Try this in the stable first by offering a bucket of water directly to your horse in hand and you will find he is quick to investigate, especially if you have been offering treats through the hole in the muzzle.
• Don’t leave the muzzle on all day. 
• Move your horse off the grass when he is not wearing the muzzle, to prevent him from grazing freely and trying to compensate for previously restricted grazing.
• Be aware of herd dynamics and ensure that the horse wearing the muzzle is not being bitten by others in the group. 

Related: ThinLine Reinvents Grazing Muzzle

Fit and Comfort of a Grazing Muzzle

By Kathy Smith

Photo: ©Chelle129-Fotolia.com

While the horse may not welcome the restriction of his access to lush spring pasture, the horse’s owner may also become frustrated when trying to find a muzzle that provides a comfortable fit. 

Here are some tips to help:

• The grazing muzzle should fit snugly, with about an inch of space between the bottom of the muzzle and the horse’s nose. A poorly fitted muzzle – either too loose or too tight – can cause rubbing. A guideline width of two fingers between the bottom of the chin and the muzzle will allow room for chewing but not so much room that the muzzle may become stuck in the horse’s mouth or removed entirely.
• Pad the parts of the muzzle that come into contact with the horse with lambskin or synthetic fleece to prevent rubbing on top of the nose, and under the chin. If hair loss is noticed, apply zinc oxide cream.
• Reinforce the muzzle with straps attached with buckles if the muzzle won’t stay in place.
• If the muzzle is designed to be attached to a halter, choose a leather halter, or a nylon halter with leather crownpiece that will break should the muzzle get caught on something. Dedicate the halter for this use, and keep the muzzle and halter as a single unit once the muzzle has been fitted to the halter.
• Check the horse daily for rubs, and keep the grazing muzzle-halter combo free of dirt and debris.

To read more by Kathy Smith on this site, click here.

Related: Slower Feeder Safer Feeding

Main Photo: ©Shutterstock/Linda George