Forage nutritive value and steer responses to grazing intensity and seed-head suppression of endophyte-free tall fescue in mixed pastures1

A 2-yr grazing experiment was conducted with 8- to 10-mo old steers on pastures of endophyte-free tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] in mixture with other grasses to assess the effect of seed-head suppression of fescue on steer performance and forage nutritive values. Treatments with and without seed-head suppression were each combined with either light or moderate grazing intensities for assignment to twelve 1.0-ha pastures of the grass mixtures. The experiment was conducted as a randomized complete block design with 3 replications. Steer ADG was measured, and CP and in vitro DM digestibility (IVDMD) of available forage, and leaf blade and sheaths of fescue tillers, were monitored. Averaged over grazing intensities, ADG was 16% greater (P < 0.05) with seed-head suppression; however, a lower (P < 0.001) mean stocking rate with seed-head suppression resulted in a tendency of greater (P = 0.068) BW gain per hectare without suppression. Crude protein of available forage was consistently greater (P < 0.01) with seed-head suppression across all dates, whereas IVDMD was consistently greater (P < 0.01) with seed-head suppression in the late grazing season. Crude protein in leaf blades and sheaths of vegetative tillers with seed-head suppression were consistently greater (P < 0.01) than vegetative tillers without seed-head suppression. The IVDMD of blades and sheaths was similar (P > 0.18) between suppressed and nonsuppressed vegetative tillers, and both had greater (P < 0.05) IVDMD than reproductive tillers over most dates. Results showed seed-head suppression of fescue to improve steer ADG by increasing CP in vegetative tissues and improving digestibility of available forage by alleviating lower-quality, reproductive tillers.