Rotational grazing system for beef cows on dwarf napiergrass pasture oversown with Italian ryegrass for 2 years after establishment

Abstract

AbstractWe examined an intensive rotational grazing system for dwarf and late‐heading (DL) napiergrass (Pennisetum purpureum Schumach) pasture in a summer period, and an oversown Italian ryegrass (IR) pasture in a winter period for the 2 years following establishment. Four 0.05‐ha paddocks of DL napiergrass pasture (20 m × 25 m) were established on 6 May 2002. They were rotationally grazed for 1 week, followed by a 3‐week rest period by 2–3 breeding or raising beef cattle (Japanese‐Black) for three and six cycles in a summer period during the first and second years of establishment, respectively. In the IR pasture, which was established by oversowing IR in both years, rotational grazing by 3–4 animals was conducted in March and April for two cycles of grazing for 1–2 days in each paddock in 2003 and for 3–5 days in all four paddocks in 2004. In the DL napiergrass pasture before grazing, the plant height, leaf area index and the ratio of leaf blade to stem were highest in the hot summer season, while tiller number increased and herbage mass tended to increase as grazing occurred, except for the first grazing cycle both years, and for one paddock in the second year. Herbage consumption, rate of herbage consumption and dry matter intake tended to decrease in three paddocks from the first to the third cycle in the first year, while herbage consumption and rate of herbage consumption tended to increase as grazing occurred in the second year. Dry matter intake averaged 10.2–14.5 and 15.4–23.2 g DM kg−1 liveweight (LW) day−1 over the four paddocks in the first and second year, respectively, and average daily gains were 0.09 and 0.35 kg head−1 day−1 in the first and second year, respectively. In the oversown IR pasture, herbage consumption tended to increase as grazing occurred, and the average daily gains were 1.49 and 1.36 kg head−1 day−1 in 2003 and 2004, respectively, except for the LW decrease during the first cycle in early March 2004. The carrying capacities on DL napiergrass pasture and IR pasture were estimated at 1016 and 208 cow‐days (CD) ha−1, respectively (annual total 1224 CD ha−1) in the first year and at 1355 and 207 CD ha−1, respectively (annual total 1562 CD ha−1) in the second year. Thus, DL napiergrass pasture oversown with IR can expand the grazing period for beef cows to late November, March and April, in addition to the summer season for the 2 years following establishment.