264. Performance of Cow–calf Pairs and Stocker Cattle Rotationally Grazing Sudangrass with or Without Sunnhemp During Summer.

Abstract A decline in cool-season pasture productivity during summer creates a gap in high-quality forage availability. Warm-season annual forages such as sudangrass (Sorghum × drummondii) can be used to address this limitation, and inclusion of annual legumes such as sunnhemp (Crotalaria juncea) may improve forage quality and animal performance; however, limited research has evaluated its impact in grazing systems. Therefore, the objective of this study was to evaluate the effects of a sudangrass monoculture (MONO) vs. a sudangrass–sunnhemp mixture (MIX) on carrying capacity and animal performance of beef cow/calf pairs and growing steers. Over 3 years, forage types were seeding in early June, with grazing starting in Mid-July. The sunnhemp was added at 50% of the seed weight. For carrying capacity, the study design was a randomized complete block with a 2x2 factorial design for forage type (MIX vs MONO) and class of cattle (pairs vs growing steers). For animal performance, the study design was a randomized complete block design. Two 20-ha fields were divided into 4 pastures with each field (block) containing one replicate of each forage type and cattle class combination. Both the location of each cattle class and the forage type was assigned randomly within block in year 1 and remained in the same location in subsequent years. Pastures were sized such that cow/calf pair pastures were larger ∼6 ha compared to grazing steers ∼3.5 ha. Cow/calf pairs (n = 51, 44, and 48 testers in year 1, 2 and 3) were stratified by dam age (4-12 yr) and randomly assigned (9 to 13 per group). Mean initial cow BW 663 ±65kg and calf initial BW averaged 122 ±24kg. Growing steers (n = 51,46 and 40 testers in year 1, 2 and 3) were stratified by initial BW (408 ± 20kg) and assigned randomly to group (11 to 13 per group). Groups were rotationally grazed among 4 paddocks per pasture. Carrying capacity was not different (P = 0.75) at 6.77 and 6.70 AUM/ha for MIX and MONO, respectively, over a 56 ± 10 day grazing period. Nursing calf ADG (3 years average 1.1 ± 0.2kg) and change in cow BCS (average change 0.16 BCS) were not different (P ≥ 0.69) between treatments. However, growing steers grazing MIX tended (P = 0.07) to have greater ADG compared to MONO at 0.72 vs. 0.66 kg/d, respectively. Overall, inclusion of sunnhemp in sudangrass pastures did not improve carrying capacity or performance of cow/calf pairs but may provide a modest advantage for growing steer gains.