We see a large number of horses at our practice that are overweight, and most of the time the excess weight is due to consumption of pasture grass. The concern about this weight condition is that a number of these horses have equine metabolic syndrome, and pasture consumption can lead to laminitis and founder. So it is important to decrease consumption of pasture grass, yet this can be difficult in some cases. The most obvious option is to just maintain the horse on a dry lot. However, this is difficult for many people to have a dry lot large enough that the horse can get adequate exercise. Another option is to allow the horse to graze just a short period of time every day. Unfortunately, studies have shown that horses consume a large amount of the pasture that they going to consume in a 24-hour period in the first three hours they are turned out on the pasture, so just turning the horse out for a short period is not going to work.
Another option that has been used successfully is a grazing muzzle. The advantage of a grazing muzzle is that the horse can be turned out on regular pasture to get exercise and be with the other horses and yet not eat too much pasture grass. One study indicated that a grazing muzzle decreased pasture consumption by 83%, which is certainly significant. However, a group out of Minnesota published a study in the Journal of Equine Veterinary Science that indicated the muzzle only reduced pasture consumption by 30%, which is really not enough to prevent weight gain and laminitis in susceptible horses. For this reason, you have to be concerned if you are using only a grazing muzzle with a horse that has foundered because depending on the specific muzzle used and the type of grass, your horses could still founder while wearing a grazing muzzle.
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