Eeffect of pre-grazing grass height on herbage production and utilization under rotational grazing of lactating dairy cows on perennial ryegrass dominant pasture

摘要

Effects of pre-grazing grass height (PGGH) on the herbage production (HP) and utilization (HL) were studied on 2 perennial regrass-dominant pastures (0.94 ha) under rotational grazing by lactating dairy cows. Each pasture was divided into paddocks and rotationally grazed by 7 cows (for 5 hours daily) from May to October, with target PGGHs of 20cm (GH20) at one pasture and 30cm (GH30) at the other, being controlled by adjusting grazing intervals. The mean PGGH over the grazing season was 20.4 and 30.1 cm for GH20 and GH30, respectively. HP before and during the grazing season was 1.4 and 7.9t DM/ha for GH20, and 3.4 and 7.11 DM ha for GH30, respectively. Total HU was 9.0 and 9.91 DM/ha for GH20 and GH30, respectively. PGGH, daily HP and HU in GH20remained relatively constant throughout the grazing season, except for a decline in herbage production in October. On the contrary, PGGH, daily HP and HU in GH30 showed considerable fluctuations with peaks in June or May-June. Between GH20 and GH30. there was no difference in total UP and HU, while seasonal fluctuation of daily HP and HU in GH30 was greater than that in GH20.