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Forage production and stocker cattle performance on BMR sudangrass and vegetative corn in upper Midwestern grazing systems
Warm season annual grasses have potential to increase carrying capacity for grazing systems in the Midwest. A study was conducted to test brown mid-rib sudangrass (SG) and corn for carrying capacity. Pastures of 1.14 ha were strip grazed with a “put and take” method involving eight 0.14 ha paddocks with a 3-day rotation frequency. At least four Holstein “tester” steers (318 ± 4 kg, mean ± SEM) were assigned to each of six pastures. Additional “non-tester” steers were added when biomass was greater than the estimated intake for tester steers (dry matter intake estimated at 3% body weight) over 3 days with assumed grazing efficiencies of 60% in SG and 90% in corn. Forage data were analyzed as a completely randomized design with week as a repeated measure and pasture as the experimental unit. Weight measurements were taken on two consecutive days before and after each 24 day grazing cycle. Tester steer Daily gain was averaged and analyzed as a completely randomized design with pasture as the experimental unit. Stocking rates for corn were 14.2 ± 0.5 steers/ha or 4650 ± 163 kg/ha and 7.1 ± 0.5 steers/ha or 2380 ± 163 kg/ha on SG. Measurements for pre- and post-grazing biomass were taken weekly in both treatments. For SG, three 0.61 m2 quadrats were randomly set in each paddock and clipped 5 cm from the soil. For corn, three 3.05 m sections of row were randomly selected and harvested 5 cm from the soil. Grazing commenced when the corn treatment reached V7 and the SG reached 72 cm. Corn was strip grazed once, while SG was strip grazed twice with the second 24 day grazing cycle following a 40-day rest period. Pre grazing biomass was higher (P < 0.05) in corn averaging 2550 ± 261 kg/ha, while SG averaged 1980 ± 261 kg/ha. Harvested forage was also higher (P < 0.05) in corn averaging 2428 ± 255 kg/ha and 1780 ± 255 kg/ha for SG. Average daily gain was not significantly different (P = .37) between treatments (1.0 ± 0.12 kg/d vs. 0.84 ± 0.12 kg/d, for SG and corn). There was also no difference (P = .41) between gain per ha (285 ± 48 kg/ha for corn and 348 ± 48 kg/ha for SG). The same gain per hectare was achieved with a lower stocking rate and greater grazing days when SG was grazed.
Keywords: grazing sudangrass stocker