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Stocking management effects on forage composition, cow methane emissions, and soil properties of cool season pastures
Forty-eight multiparous August-calving Angus cows (627 + 63.8 kg [2012, yr 1], 552 + 62.0 kg [2013, yr 2], 614 + 51.8 kg [2014, yr 3]) were allotted to six 4.04-ha cool season grass-legume pastures to graze by continuous (CONT), rotational (10 paddocks; ROT), or strip (10 paddocks with a mobile fence; STP) stocking from May to October. Daily live forage allowances in ROT pastures were 4.0, 4.8, and 6.0% BW from May 11, August 1, and September 14 in yr 1, 4.0, 6.0, and 7.2% BW from May 14, July 22, and August 19 in yr 2, and 4.8 and 6.0% BW from May 12 and August 1 in yr 3 with a single hay harvest from 40% of the area in yr 1 and 2. Daily forage allowances in STP pastures were one-half those in ROT pastures with no hay harvest. Forage was sampled to a height of 2.54 cm from each pasture, weighed, and analyzed for DM, IVDMD, NDF, ADF, and CP monthly. Methane emissions from 2 cows per pasture were estimated utilizing sulfur hexafluoride over 7 d beginning on June 21 and August 8 in yr 2 and June 19 and August 12 in yr 3. Simultaneous to methane measurements, forage was sampled from the top half of the sward in CONT pastures and in the stocked paddock of ROT or STP pastures. Live forage was separated and analyzed for DM, IVDMD, NDF, ADF, and CP. Soil penetration resistance, bulk density, and OM content were measured along six transects from the water source in CONT pastures and in one paddock of each ROT or STP pasture in May of yr 1 and October of yr 3. Monthly forage mass and composition differed little between treatments. However, during methane emission measurements, IVDMD and CP concentrations were greater (P < 0.05) and NDF concentrations lower (P < 0.05) in live forage in the upper canopy of ROT than STP pastures in August. There were no significant treatment effects on daily methane emissions per cow. In October of yr 3, soil bulk density did not differ between treatments, but soil penetration resistance at depths of 0, 12.5, and 15.0 cm were greater (P < 0.05) in CONT than STP pastures. While STP at a limited forage allowance reduces forage quality, it does not significantly affect methane emissions while reducing soil penetration resistance.
Keywords: cattle, grazing, methane