to over ½ from midvegetative stage (2 to 4 weeks of growth and mature height) to seed-forming maturity (12 weeks of growth). These decreases are well demonstrated by the results of the study shown in Table 5–2. Although both types of forage in the study were high in nutritional value in the spring, by winter they were quite low. The concentration of some minerals also decreases with plant maturity. From 2 weeks to about 8 weeks of maturity, the concentrations of potassium, phosphorus, magnesium, manganese, and iron decrease by about one-half, whereas there is little change in calcium, zinc, or sodium. Phosphorus, copper, and protein concentrations in pasture forage decrease from spring to summer then increase with regrowth that fall (Table 5–3). Thus, if forage is grazed or cut late in maturity, its available dietary energy, protein, and palatability are low; if harvested too early, the amount of feed or forage obtained is low. A good balance between these factors and, thus, the best time to graze or cut pasture forage for hay is just prior to flowering (bud stage) or emergence of the heads. For alfalfa, this is generally when the plant is about 8 inches (20 cm) tall. Many pastures begin to change from an emerald green color to a darker green to a slightly gray color at the best time for harvesting, then with increasing maturity to full-bloom color, if it contains blooming species, then to yellowish brown. Proper pasture and grazing management are necessary if the horse is to obtain the maximum total amount of nutrients and, therefore, benefit from the pasture year after year.

HORSE GRAZING BEHAVIOR

Knowledge of the horse’s grazing behavior may be helpful in managing grazing to maximize the nutrients obtained from pasture forages, and to maximize pasture benefit for the horse’s physical and psychologic well-being. The amount of time horses devote to grazing and other activities varies considerably with changes in their environment. The time devoted to grazing decreases with severe weather (hot or cold), increased pasture forage availability, being alone, and flies, and is less in young horses. Variation in individuals commonly occurs. Mature horses, domestic and feral, on pasture with ample forage and no other feed during mild weather are reported to spend from 40 to 60% of a 24-hr period, and 60 to 80% of daylight hours, grazing, with the most continuous grazing, periods being early morning, late afternoon and evening, and the middle of the night. The normal pattern is to graze continuously for several hours, and to rest for longer or shorter periods, depending on weather conditions and distance that must be traveled to obtain water and sufficient forage. Grazing time is inversely proportional to the quality and amount of pasture forage, e.g., high quality and high amounts result in low grazing time. Horses also spend 9% of their time walking (more on poor pasture or if alone, presumably in search of companionship), and 5 to 10% of their time, primarily during the period 3 to 4 hours before dawn, lying down, with 25 to 30% of this on their side. Individually stalled horses with free access to hay spend a similar amount of their time eating: 73% of daylight hours when they could see other horses and 60% when they couldn’t. When individually confined to a pen, mature horses spend 57% of the time eating hay, and 10% lying down. Even on the foal’s first day of life, it spends 6 to 9% of its time grazing, with this increasing to 23% by 1 to 8 weeks of age, to 40 to 50% by 21 weeks, and as yearlings to the same as adults.

TABLE 5–1 Nutrient Content of Mixed Central Kentucky Pasture Forage^a

TABLE 5–2 Forage Maturity Effect on its Digestibility and Digestible Protein Content for the Horse

Horses are selective grazers. They do not simply eat from plants that are in the greatest abundance. They base their selection on palatability as well as availability. Until preferred forages are depleted, horses will eat only a few of many species available. Stage of growth, also determines seasonal difference in preference, the younger more immature plants being preferred. These preferences result in spotty grazing and incomplete utilization of pasture forage, which can be minimized with proper pasture grazing management.

GRAZING MANAGEMENT

The horse will eat, trample, or damage forage that is equivalent to at least 1000 lbs (454 kg) of hay per month. Forage production of pasture in most areas occurs during a 5-to 7-month period. During this period, one acre (0.4 ha) of good, improved pasture receiving the optimum amount of moisture (irrigation or precipitation) may yield the equivalent of 5 to 7 tons (11 to 16 MT/ha) of nutritious, high-quality forage. Thus, one acre (0.4 ha) of these types of pasture would support two mature light-breed horses during this period. In contrast, 30 to 60 acres (12 to 24 ha) of dry range pasture, typical of that in the Rocky Mountain Great Plains area of the United States, may be needed to support a single horse for one year.

TABLE 5–3 Plant Maturity Effect on Pasture Forage Nutrient Content^a

For maximum pasture forage production, horses should not be on the pasture during or shortly after precipitation or irrigation. Adequate time should be allowed for drying of pastures to minimize trampling, plant injury, and soil compaction. Irrigation should be at intervals that do not permit plants to be stressed. Ideally, the soil should not become dried out below the top two inches (5 cm). The approximate amount of total annual water (from precipitation or irrigation) needed for optimum pasture forage growth is 24 to 36 inches (60 to 90 cm).

On pastures of blucstem, smooth brome, crested wheat grass or legumes such as alfalfa or clover, or on native pastures in the Rocky Mountain-Great Plains area of the United States, only 50 to 60% of the forage should be removed by grazing. Grazing in excess of this is harmful to the plants and slows regrowth, so that over several years the average yearly yield is lowered. In contrast, Kentucky bluegrass, digit, bahia, and orchard and Bermuda grasses, which are the most common pasture grasses in many areas of the southern United States, do best when grazed intensively and cropped closely. These grasses should be grazed at early flowering or before, at which time their feeding value is greatest. At this time, they may provide up to 1.2 megacalories of digestible energy (Mcal DE)/lb (2.6/kg) and over 20% crude protein in their dry matter, as compared to 1.45 Mcal DE/lb (3.2/kg) and 10 to 13% crude protein in oats. This illustrates why young horses grow rapidly and mature horses may become overweight on lush, green growing pasture forage, which is almost like allowing them to eat all the oats they want 24 hours a day, along with some additional protein and fiber.

Once the pasture forage is eaten down to the proper level, all grazing animals should be removed, and if the pasture is to be irrigated, it should be done at once. Over grazing should be prevented. The short-term gain from the small amount of additional forage obtained by overgrazing is more than offset by the long-term loss of decreased for age growth. As a result, an increased amount of generally more expensive feed must be fed. Overgrazing is a good example of being “penny wise and dollar foolish.” Over grazing slows or prevents forage regrowth, which allows weeds to invade the pasture and replace desirable plants. To prevent this, the pasture forage preferred by the horse should not be grazed to less than 2 inches (5 cm) in height. However, to obtain the greatest forage production and thus benefit from pasture, it is better: (1) to remove all grazing animals from the pasture when the preferred for age is eaten down to the amount recommended, except in the late fall as the plant’s dormant season nears, when 4 to 6 inches (10 to 15 cm) of plant height should remain; and (2) not to put them back on the pasture until shortly before plant growth but not seed production is nearing completion, as described in the previous section. To prevent overgrazing, horses must be removed from the pasture. Feeding additional feed and leaving them on the pasture won’t prevent overgrazing. Even if they are fed grain and have ready access to good hay, they will continue to graze, particularly the more succulent young grass, so short that regrowth can’t occur or is slowed.

The length of time horses may be maintained on a pasture without overgrazing it can be extended by shutting them off the pasture, having hay available for at least 4 hours or more before they are put back on the pasture, and leaving them on the pasture for only a few hours daily (or less, the longer you want to extend the number of days the pasture can be grazed). Although the horse continually on pasture will graze 14 to 16 hours per 24-hour period, if there are adequate quantities of good-quality pasture for age readily accessible, they can consume a sufficient quantity to meet their dietary energy needs for maintenance in 4 to 5 hours daily.

When horses are on a pasture providing an adequate amount of average quality forage for only a few hours a day, they will eat about one-third lb/100 lb body/wt/hr 1/3 kg/100 kg/hr). This is reduced to about one-tenth lb/100 lb body wt/hr (0.1 kg/100 kg/hr) when they are on pasture 24 hours a day. However, the rate of consumption varies directly with pasture-forage quality, digestibility, and palatability.

The key to obtaining the greatest feeding value from pasture is (1) not overgrazing it, and (2) utilizing its forages while they are in the young growing stages of development. As forages mature, their palatability and utilizable nutrient content decrease rapidly (Tables 5–2 and 5–3). As a result of the mature plants’ reduced palatability, horses won’t eat them, and instead will overgraze the more palatable plants which are trying to grow. The result is increased weeds in the overgrazed areas, and in the undergrazed areas wasted forage and increased feces. The increased manure contributes to uneven grazing because most mature horses avoid grazing fecally contaminated areas. The plants in these areas grow rapidly due to the added fertility from the manure, producing lush but rapidly maturing forage that, because of both the increased manure and plant maturity, remains ungrazed. To correct patchy grazing once it occurs, spray or mow the weeds, then mow the overmature forage close to the ground, and, finally, scatter the manure with a wire or chain drag or harrow. The way to decrease it from occurring is to not allow any portion of the pasture to be overgrazed and to either harvest the pasture forage or use rotational grazing.

Rotational Grazing

If there is adequate pasture available, the greatest benefit from it for grazing can be obtained by dividing it into two to four similar-size pastures and using rotational grazing (Fig. 5–1). Rotational grazing provides the best opportunity to obtain maximum forage yield. Ideally, each pasture should be just large enough so that the animals to be put on it will consume all the forage produced on it in 10 to 14 days during plant growing seasons. If the stocking rate is not high enough to totally utilize the pasture, spot grazing will occur and mowing may be necessary to rid the pasture of the tall mature grasses that the horses did not graze. Following the 10-to 14-day grazing period, the pasture should have about a month’s rest for new for age growth to occur before the horses are rotated back onto it.

As shown in Table 5–4, in one study, more than twice as much forage was obtained from the same amount of initially similar pasture by rotational grazing. The greater amount of forage obtained was due to the forage growth that occurred when the pasture wasn’t being grazed, and because spot grazing didn’t occur in the rotationally grazed pastures but did in the continually grazed pasture.

Fig. 5–1. Dividing an acreage into several pastures so that rotational grazing of each pasture may be used provides the best opportunity to obtain maximum forage production. (Courtesy of Moon-drift Farm, Fort Collins, CO)

Although pasture can usually be divided easily using an electric wire, if several pastures are not available and, therefore, rotational grazing isn’t possible, patchy grazing may be minimized using intermittent grazing. Put the horses on the pasture as its forage approaches maturity, or earlier, if necessary, so that all pasture forage will be eaten to the proper level within 10 to 14 days. At that time, the horses should be removed from the pasture until its forage is ready for the next grazing period.

Grazing cattle or sheep with horses will also decrease patchy grazing. Although horses and cattle show a large overlap in choice of forage, horses tend to graze only particular areas in the pasture while cattle and sheep graze more at random. Other types of livestock will also graze around manure piles left by horses while most horses tend to avoid these areas. In contrast to cattle, there is little overlap between horses and deer in choice of forages and browse; thus, their presence on the same pasture doesn’t decrease the feed available for the other species. Instead, a combination of livestock keeps pastures grazed more uniformly and helps maintain the pasture’s forage in the high-quality growth stage. The combination not only makes more efficient use of the pastures, but also offers additional income from the pasture. Cattle, sheep, and horses may all graze the pasture at the same time, or the cattle or sheep may follow the horses on the pasture. Cattle also are able to utilize a greater amount of dietary energy, but less protein, from grass, but not alfalfa, than are horses. However, their protein requirement is lower than horses (6 versus 8%, except during lactation and growth). The more mature the forage, the greater the difference between horses’ and catties’ digestibility of it. Thus, cattle may get by on more mature, lower protein forage than can horses.

TABLE 5–4 Rotational versus Continual Grazing Effects on Yearling Horses and Forage Production

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