Annual warm-season grasses have the potential to provide forage, but are rarely evaluated under horse (Equus caballus) grazing. The objectives were to determine yield, forage nutritive values, and preference of annual warm-season grasses at different maturities under horse grazing. Horses grazed Japanese millet [Echinochloa esculenta (A. Braun) H. Scholz], Siberian millet (E. frumentacea L.), teff [Eragrostis tef (Zucc.) Trotter], sorghum sudangrass brown midrib (BMR) (Sorghum bicolor × S. bicolor L. var. sudanese), sudangrass [S. bicolor (L.) Moench ssp. drummondii], and annual ryegrass (Lolium multiflorum Lam.) at vegetative and mature stages in Minnesota; annual ryegrass served as a control. Sudangrass had the highest yield (P ≤ 0.01), producing ≥5.5 Mg ha–1 at the vegetative stage and ≥9.7 Mg ha–1 at the mature stage. Siberian millet produced the lowest yields at the vegetative (≤2.5 Mg ha–1) and mature (≤6.0 Mg ha–1) stages. While all grasses met the nutritional requirements of many classes of adult horses, an inverted Ca to P ratio and high nitrate-nitrogen (NO3–N) levels were observed. Annual ryegrass was most preferred (P ≤ 0.01) with ≥60% removal at the vegetative stage and ≥40% removal at the mature stage. Siberian millet was least preferred with ≤40% removal at the vegetative stage and ≤5% removal at the mature stage. Based on maximizing yield, forage nutritive values, and preference, teff, sudangrass, and sorghum sudangrass show potential as annual warm-season horse pasture forages; however, Ca/P and NO3–N should be determined before initiating grazing.