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Pasture Quality and Abundance Affects Contribution to Horse DietsBy Kentucky Equine Research Staff · January 2, 2012

Pastures intended for horses are not always the lush, green expanses depicted in tourist brochures for central Kentucky.Those pastoral scenes are stunning, but not every horse has access to such bountiful grazing.

Forage should be of primary importance when considering the equine diet. Hay, pasture or alternate forage sources should often make up the majority of a horse’s total ration. The horse has a minimum requirement for forage intake equal to 1% of his ideal body weight. This is frequently lower than the suggested minimum intake recommended and will also likely differ from the typical intake.

It is the gaps left between what is supplied by the horse’s forage intake and the digestible energy and nutrient requirements of the horse that we seek to fill by adding grains and supplements to the ration. However, it may be difficult to determine how much forage the horse consumes per day and how much that forage contributes to the the nutritional and caloric requirements of the horse.

Horses allowed full-time turnout may spend up to 65% of their time grazing and will generally consume 1-1.4 lb (0.45-0.64 kg) of dry matter per hour if enough pasture is available. This is, of course, an estimate and your own horse’s behavior may differ. Spending time engaged in nongrazing activities such as cribbing or walking the fence will likely lower intake rate. Likewise, some individuals are highly motivated and may consume over 2.2 lb (1 kg) of dry matter per hour.

Fresh forage consumed from grazing pasture can make a significant contribution to the horse’s diet. For example, a 1,200-lb (545-kg) horse allowed constant turnout might consume anywhere from 16 to 22 lb of dry matter when turned out on well-managed, thick pasture. This amount is more than enough to satisfy the horse’s absolute minimum requirement (1% of body weight, equal to 12 lb or 5.45 kg) as well as exceed the recommended minimum forage intake (1.5% of body weight, equal to 18 lb or 8.2 kg) per day. Additionally, the amount consumed may meet nearly all or even exceed an idle, lightly worked, or pregnant horse’s energy needs. In fact, significant intake of this type of pasture can contribute over half of the digestible energy needed by horses engaged in moderately intense exercise.

Recent research has shown that limiting access to pasture, especially if part of a learned routine, can affect the rate of intake. A study with ponies revealed that limiting turnout from full time to three hours per day increased rate of intake to such an extent that ponies went from consuming 0.49% to 0.91% of their body weight, equivalent to an impressive 2.42 lb (1.1 kg) of dry matter per hour. The same study found that using a grazing muzzle was highly effective at lowering intake rate, lowering it to 0.37 lb (0.16 kg) per hour. Similar phenomena are likely observed in horses as well.

While it would make life easier and certainly lead to standardized calculations for forage intake from pasture and reduced hay expenditures, not all pastures are equivalent to the best-quality, lush pasture. In order to estimate the likely contribution of pasture to your horse's forage and other requirements, you should first evaluate the quality and abundance of the pasture available. This should be done with an eye toward grading the pasture based on the level of forage intake it has the potential to support.

Turnout spaces can be classified into five broad categories: drylot, poor, fair, moderate, and best. A description of each pasture type follows.

A drylot is any area where horses are turned out and are able to move about freely, but is free of any vegetative matter. This could be a sand or gravel run connected to a stall or turnout paddock. This area is for free exercise only and will not provide any forage intake. A drylot is ideal for horses that must consume carefully regulated diets such as easy keepers or those diagnosed with certain metabolic diseases. Horses with drylot turnout alone will be entirely dependent on supplemental forage sources such as hay, chaff, forage cubes or pellets, or alternative fiber sources.

Poor-quality pastures may contain a mix of grass and/or legume species. However, weeds or other nongrazed species may account for the majority of vegetative matter. Pasture will likely be overgrazed with areas of short-grazed species, bare spots, and rough, weedy areas. Height of grazed species will typically be consistently grazed very near to the ground. This pasture will not support the maximum dry matter intake per day. Horses could consume approximately 25% of maximum dry matter needed on this pasture.

Fair-quality pastures may have a mix of grass and/or legume species and may be more thickly interspersed with weeds or other nongrazed species. Pasture will be unevenly grazed with roughs and lawns (closely grazed areas) and will have notable bare spots. Plant height typically will be inconsistent and range from 1-6 inches in height. This pasture will not support the maximum dry matter intake per day. Horses may consume approximately 50% of maximum dry matter needed on this pasture.

Moderate-quality pastures may have a mix of grass and/or legume species interspersed with weeds or other nongrazed species. Pasture will be unevenly grazed with roughs and lawns (closely grazed areas) but will have minimal bare spots. Plant height will typically be inconsistent and range from 1-6 inches in height. This pasture will not support the maximum dry matter intake per day. Horses might consume approximately 75% of maximum dry matter needed on this pasture.

Best-quality pastures contain a thick stand of grass and/or legume species with minimal weeds evident, few or no bare areas, and even distribution of grazing across the pasture. Plants are kept at a height of 6-10 inches by regular mowing. This pasture will support maximum rate of dry matter intake.

Once you have graded your pasture quality, you are much closer to estimating the amount of forage your horse can likely consume based on the amount of time it’s allowed to graze. This will increase your understanding of how much the horse’s pasture intake contributes to his overall ration, allowing you to judge how much additional forage (hay, chaff, or other forage products) should be offered. Conversely, with easy keepers or overweight individuals, you may find that, based on the pasture quality and time on pasture, methods for restricting pasture intake may be indicated.

You should note that pasture quality is not static; it can change over time due to the effects of weather, season, and management. Therefore, changes in pasture quality and abundance should be accompanied by appropriate adjustments to the horse’s ration in order to maintain a steady plane of nutrition.

By working with a qualified equine nutritionist, you can choose the best options for satisfying your horse’s forage needs.

More reading:
Pasture Adequacy: Are Your Fields Doing Their Job?
Revelations About Ponies and Pastures
Stocking Rate: How Many Horses on This Pasture?
Horse Pasture Management
Hay: The Favorite Lunch Munch for Horses