Sward Structure of Simple and Complex Mixtures of Temperate Forages

Sward composition and structure influence herbage intake of grazing animals. We conducted a grazing study to examine how forage mixture complexity affected sward structure. Replicated 1-ha pastures (Hagerstown silt loam soil: fine, mixed, semiactive, mesic, Typic Hapludalf) were planted to either orchardgrass (Dactylis glomerata L.) and white clover (Trifolium repens L.) or a nine-species mixture [orchardgrass, tall fescue (Festuca arundinacea Schreb.), perennial ryegrass (Lolium perenne L.), Kentucky bluegrass (Poa pratensis L.), red clover (Trifolium pratense L.), birdsfoot trefoil (Lotus comiculatiis L.), white clover, alfalfa (Medicago sativa L.), and chicory (Cichorium intybus L.)]. Pastures were stocked rotationally with lactating dairy cows (Bos taurus). Herbage mass, sward height, vertical structure, and nutritive value were measured pre- and postgrazing during four periods in each of 2002 and 2003. Pregrazing sward height was similar between the mixtures. Pregrazing herbage mass and sward bulk density were 30% less in the two-spedes mixture than the nine-species mixture in 2002 but similar in 2003. The nine-species mixture had more herbage dry matter in the upper sward layers than the two-species mixture. Bulk density of herbage dry matter increased and nutritive value decreased from the top to the bottom of both swards. Cattle grazed deeper into the two-species sward (18 cm) than the nine-species mixture (11 cm) in 2003; however, individual botanical components in the upper 25 cm of the canopy were removed similarly between treatments. We conclude that sward structure did not alter the pattern of herbage removal during grazing of simple or complex swards.