Species selection is dependent upon climate, soil drainage, stocking density, and the class of grazing horse. Forage species are classified as grasses or legumes and must tolerate close grazing because horses are capable of extreme defoliation. Cool-season perennial grasses are adapted to the northeast USA. They are planted in spring or late-summer to provide grazing in the spring, summer, and fall, but typically yield less during the hot summer months. If possible, grazing cool-season perennial grasses should be delayed until the season after establishment to protect seedlings from the combination of trampling and frequent close grazing. Palatability also affects species preference, which varies from horse to horse. If possible, preferences should be explored before establishing or renovating a pasture. Because horses exhibit highly selective grazing patterns, individual animal preferences often result in one species favored over another until the former is overgrazed and the other too mature for consumption. Resistance to hoof traffic should factor into species selection if horses are highly active.
Kentucky bluegrass (Poa pratensis L.) reaches peak production in mid-May in the Northeast and then decreases between July and August, with the potential for summer dormancy during periods of dry weather. Kentucky bluegrass forms a dense sod, is highest palatability, and tolerates high stocking densities. It is less wear-resistant than tall fescue but rugged enough for exercise paddocks.
Orchardgrass (Dactylis glomerata L.) is an upright grass secondary to tall fescue in grazing tolerance but more palatable and shade tolerant.
Perennial ryegrass (Lolium perenne L.) is a widely used bunch grass. It has competitive, but may be less persistent than other species. Perennial ryegrass is high in dry matter digestibility and is recommended for creep grazing young, growing horses.
Reed canarygrass (Phalaris arundinacea L.) is an upright, leafy, and frost sensitive plant. It has lower palatability but is toleraant of drought, disease, and poorly drained soils. Weed competition during establishment is a problem because of its low seedling vigor, so late-summer seeding is recommended.
Orchardgrass, reed canarygrass, and tall fescue produce the greatest forage between May and June, but taper off by mid-August, with tall fescue recovering and producing the greatest regrowth through October.
Tall fescue (Festuca arundinacea Schreb.)is a deep-rooted, persistent, rhizomatous sod. It is an aggressive grass that will eventually dominate pastures and surrounding areas if not initially seeded at low rates. Growth is more restrained in a legume/grass mixture. Tall fescue is also subject to infection by an endophyte that, while increasing its vigor, causes many health problems in pregnant mares. Tall fescue is ideal for grazing horses because it is hardy, nutritious, has high seedling vigor, tolerates close grazing, destructive hoof traffic, pests, wet, and acidic conditions. Under low grazing pressure it will grow as a bunch grass, but under high pressure will appear turf-like.
The tall fescue endophyte Acremonium coenophialum produces ergot alkaloids responsible for hormonal interference in broodmares. The national percentage of infection of tall fescue is at least 85%. Seed transmission is the only mechanism for endophyte infection so planting an endophyte-free cultivar in an isolated area should eliminate the potential for infection. Endophyte-free varieties are commercially available but have lower seedling vigor, and less resistance to drought, insect pests, disease, and frequent grazing. Forage screening for Acremonium endophytes is a service offered by the Plant Diagnostic Laboratory at Rutgers University.
More information about tall fescue toxicity can be found at these web sites:
Grasses require nitrogen fertilization, while legumes form a symbiotic association with soil bacteria to convert atmospheric nitrogen to a plant-available form. Legumes are high in protein, enhance palatability and digestibility of pasture and maintain their forage quality longer than grasses. Generally legumes are not seeded at more than one-third of a grass/legume mixture by weight and have to be inoculated with the correct Rhizobia species before seeding. Legume species that spread by stolons and rhizomes may be considered for horses because their sites of regrowth are less susceptible to damage. Indigenous to the Northeast, wild white clover (Trifolium repens L.), a shallow-rooted legume with a prostrate growth habit that spreads by stolons is commonly found in pastures. The larger ladino white clover is more appropriate for use with tall grasses. Alfalfa (Medicago sativa L.) is commonly recommended because of its high yield potential, forage quality, and compatibility with grasses. However, both alfalfa and red clover (Trifolium pratense L.) do not tolerate close grazing as well as white clover.
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