Horses, as grazers, are different than every other livestock species. Notoriously known for being selective, horses can quickly turn a uniform pasture into a patchwork quilt that often results in overgrazing in some areas and nonutilization in others. Their selection habits are often difficult to explain.
University of Minnesota extension horse specialist Krishona Martinson and her co-workers have invested significant time and resources in researching horse preferences for various classes of forage species. A recent summary of that work highlighted these findings:
Perennial cool-season grasses:
• Horse preference is important to realize more uniform grazing of pastures, improved forage utilization, and a reduction in pasture maintenance (clipping or mowing).
• In pure stands, the grass species that offered the best balance of plant persistence, yield, nutrient value, and horse preference were orchardgrass, meadow fescue, endophyte-free tall fescue, and Kentucky bluegrass.
• Of the grass mixtures evaluated, horses preferred a stand of endophyte-free tall fescue, perennial ryegrass, Kentucky bluegrass, and timothy. However, over time, these pastures evolved to mostly tall fescue and Kentucky bluegrass.
• Horses had less preference for any pasture mix with 30 percent or more orchardgrass.
Annual cool-season grasses:
• Based on horse preference, yield, and forage nutritive value, annual ryegrass was shown to be a good choice for horse owners looking for supplemental forage or to extend the grazing season.
• Cereal forages (both annual and winter annual) were also evaluated but did not perform as well under horse grass grazing as annual ryegrass.
Annual warm-season grasses:
• In these evaluations, teff grass was shown to be a viable option to supplement horse forage needs during the summer slump for cool-season grasses. If used, the researchers suggested testing the crop for nitrate concentrations before grazing and monitoring the calcium to phosphorus ratio to ensure adequate calcium consumption.
• Siberian and Japanese millet did not survive for an entire growing season under horse grazing.
• Sudangrass, which was also tested, offers the potential for prussic acid poisoning, cystitis syndrome, and abortions in horses.
• All of the warm-season grasses evaluated had high levels of nitrates, but no toxicity symptoms were observed in the horses. The researchers surmised that this was probably because the animals only grazed for short periods of time and were offered other forage sources.
• Pure stands of alfalfa, red clover, and white clover were evaluated. Horses preferred the clovers over alfalfa, but alfalfa produced greater yields.
• Pure legume pastures offered a high level of nutrition and may be an option for horses with elevated energy needs. This might include broodmares, working, and performance horses. Such nutrient-dense pastures might lower the need for grain supplementation.• If maintenance-level horses are put on pure legume pastures, closely monitor the animals to ensure they don’t gain excessive body weight.