One method of decreasing weight in overweight horses is to restrict pasture access by using a grazing muzzle or confine the horse to a dry lot. However, it has been shown that restricting pasture access only results in accelerated pasture intake when grazing is eventually allowed. One study found that consumption of dry matter intake doubled for a 4-hour period after pasture restriction compared to another 4-hour period when pasture was not restricted. It has been shown that accelerated intake of grain in horses can decrease pH of the hindgut, alter fluid balance, and lead to digestive upset.
Horse's digestive systems were designed to be periodic grazers and the health of their GI tract depends on this manner of eating. A lack of pasture has been linked to increased incidence of colic in horses so pasture is important and horses spend about 60% of their time grazing while on pasture. Because horses accelerate pasture consumption after their grazing restriction ends, veterinarians at North Carolina State performed a study to determine if accelerated pasture consumption affected the horse's hindgut health the same way that accelerated grain consumption does. Horses used in the study and were allowed to graze for 24 hours while some were restricted for 12 hours and then allowed to graze for 12 hours. Results indicated that horses grazing for 12 hours on and 12 hours off have similar hindgut and fluid balance as those grazing 24 hours a day, so unlike the increase in grain eaten after restriction, there are no health concerns about accelerated pasture consumption.
Consequently, it should not be a health risk to restrict pasture access although this study did not look at all parameters. Also realize that restricted pasture access alone may not prevent obesity or laminitis.
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