Two experiments were conducted to determine the effects of grazing height and supplementation levels of Marandu pastures on average daily gain (ADG), gain per hectare (GPH) and methane (CH 4) emissions during the wet season under continuous stocking by Nelore yearling bulls. Exp. 1: three grazing heights were evaluated: 15, 25 and 35 cm, combined with 0.3% of BW of a supplement (161 g crude protein (CP)/kg and 20.1 MJ gross energy (GE)/kg on dry matter basis (DMB)). Experimental design was completely randomized (three paddocks per treatment), and the effects were analyzed by polynomial orthogonal contrasts. Exp. 2: grazing heights were combined with decreasing supplementation levels as grazing heights increased: short height (15 cm) and high supplementation (0.6% of BW of a supplement: 142 g CP/kg and 18.9 MJ GE/kg on DMB) (SHHS); moderate height (25 cm) and moderate supplementation (0.3% of BW of a supplement: 161 g CP/kg and 20.1 MJ GE/kg on DMB) (MHMS) or tall height (35 cm) without supplementation) (THWS). Experimental design was completely randomized (three paddocks per treatment), and treatment means were compared by Tukey test (P < 0.05). In Exp. 1, ADG increased linearly (P = 0.02), and GPH decreased linearly (P = 0.0002) as grazing height increased. Methane emission was not affected (P = 0.64) by grazing height. In Exp. 2, ADG was not influenced (P = 0.14) by treatments. However, GPH was the greatest (P < 0.0001) for the SHHS treatment. In addition, CH 4 emissions were lower (P < 0.0001) in SHHS and MHMS bulls compared to THWS. The SHHS Abbreviations: ADF, acid detergent fiber (expressed inclusive of residual ash); aNDF, neutral detergent fiber (assayed with a heat stable amylase and expressed inclusive of residual ash); ADG, average daily gain; AU, animal unit; BW, body weight; CP, crude protein; DM, dry matter; DMB, dry matter basis; DMI, dry matter intake; GPH, gain per hectare; ha, hectare; GE, gross energy; IVOMD, in vitro organic matter digestibility; IVDMD, in vitro dry matter digestibility; MHMS, moderate height and moderate supplementation; ME, metabolizable energy; OM, organic matter; SHHS, short height and high supplementation; THWS, tall height without supplementation.

Measurement of forage mass is critical to the management of forage allowance in grazing systems. Th e rising plate meter (RPM) was developed to monitor forage mass quickly and easily; however, it must be calibrated to provide reliable calculations of forage mass and the calibration coeffi cients may vary across seasons. Our objective was to investigate seasonal patterns in calibrations of the RPM for estimating forage mass in six cool-season grass swards in Ohio. Th e RPM reading was highly signifi cant (P < 0.01) in explaining variation in forage mass across sites and weeks; however, the RPM × week, RPM × site, and RPM × week × site interactions (P < 0.01) for forage mass indicated the relationship between RPM reading and forage mass varied among sites and over time. At one site, the RPM to forage mass relationship was investigated for three cool-season grass species, but the RPM × species and RPM × week × species interactions were not signifi cant (P > 0.05). Although there was variation among and within sites for the slope coeffi cients of forage mass regressed on RPM reading, a broadly similar seasonal pattern was found at most sites. Th e slope coeffi cients were usually high in early spring, decreased rapidly during the fi rst weeks of the growing season, and then increased from early summer to the autumn. We concluded the RPM should be calibrated at least monthly over the growing season to defi ne the seasonal pattern and changes in the slope coeffi cients for forage mass regressed on RPM readings.

________________________________________________________________________________ AbstractThe aim of this study was to ascertain whether the defoliation frequency based on a fixed rest period would generate variable sward structural and physiological conditions at each subsequent grazing event. The relative importance of the physiological age was established in comparison with the chronological age in the determination of the forage nutritive value of Xaraes palisadegrass [Brachiaria brizantha (Hochst ex A. RICH.) STAPF. cv. Xaraes]. Two grazing frequencies were defined by light interception (LI) at initiation of grazing (95% LI -"target grazing" [TG] or 100% LI -"delayed grazing" [DG]) and one based on chronological time, grazing every 28 days (28-d). Forage produced under the TG schedule was mostly leaves (93%) with a higher concentration of crude protein (CP; 138 g/kg in the whole forage), a lower concentrations of neutral detergent fibre (NDF) in the stems (740 g/kg), and higher in vitro dry matter digestibility (IVDMD) of the leaves (690 g/kg), compared to the other treatments. Lower grazing frequency strategies (DG and 28-d) resulted in forage with higher proportions of stems (10 and 9%, respectively). Strategies based on light interception did not produce pre-graze forage with a uniform nutritive value, as the indicators varied across grazing cycles. The treatment based on fixed days of rest did not result in uniformity.________________________________________________________________________________

O ne of the most important measurements for pasturebased livestock producers is herbage mass. This measurement can help producers to ensure that pastures are managed so as to avoid under-and overuse by grazing animals and to help calculate animal intake. It is important to maintain herbage mass within an appropriate range to avoid both a reduction in the forage accumulation rate and forage availability to the animal (Barker et al., 2010). However, when feeding animals with high nutritional requirements (e.g., dairy), the nutritive value of the forage must also be considered. Nutritive value is defined as the in vitro disappearance and chemical composition of forage (Mott and Moore, 1985) and is often expressed using crude protein, in vitro dry matter (DM) (or organic matter) disappearance, neutral detergent fiber (NDF), acid detergent fiber, and lignin concentrations (Sollenberger and Vanzant, 2001). The digestibility of cool-season grasses declines as they mature during spring (Minson et al., 1960). The development

A gronomy J our n al • Volume 102 , I s sue 3 • 2 010 849 ABSTRACT Sigmoid equations are recognized as representative of the pattern of herbage accumulation during a growth period; however, the various equations and their variability among locations and during the growing season have not been well described. Th e objectives of this study were to fi nd the most suitable, four-parameter sigmoid equations to fi t measured herbage mass and to investigate how the patterns of herbage accumulation (i.e., equation parameters) varied with time of year and location. Herbage mass was measured approximately weekly during 11 to 12 growth periods with a rising plate meter (RPM) at three north-central United States locations (Columbus and Coshocton, OH, and Arlington, WI) during 2008, and those data were fi t to Gompertz equations. Th ere were four replicates for each growth period. We found predictable relationships between instantaneous herbage accumulation rate (HAR i ) and herbage mass for each location and date. Time-independent HAR i vs. herbage mass curves have potential use for pasture management by defi ning the optimum herbage mass at which HAR i is maximum. Th e optimum herbage mass varied between 1600 and 4000 kg dry matter (DM) ha -1 depending on location and date. Allowing herbage mass to exceed the optimum point (e.g., delayed harvest), or harvesting to below the optimum point, will reduce the HAR i . Th e HAR i -herbage mass curves defi ne a range of herbage mass within which pastures can be managed to achieve high HAR i , and maintaining pastures within 90% of the maximum HAR i may be a practical target for producers.