Performance of stocker cattle grazing 2 sorghum-sudangrass hybrids under various stocking rates

Summer annual forages are a practical roughage source for stocker cattle operations because of their high yield potential. A 2-yr study was conducted to compare the performance of steers grazing 2 different varieties of sorghum-sudangrass hybrids at different stocking rates. Brown midrib (BMR) and photoperiod-sensitive (PS) sorghum-sudangrass hybrids were selected based on differences in nutritional value and yield. Twelve experimental pastures (6 per variety) were established and grazed by steers (231 ± 4 kg) for 84 d each year at stocking rates ranging from 2.33 to 4.10 animal units per hectare per 84 d (3.6 to 6.4 steers/ha). Initial (0 d), intermediate (28 and 56 d), and final (84 d) cattle BW was used to calculate ADG and gain per hectare. Forage samples were also collected at 28-d intervals to assess quality and quantity of standing forage. Regression analysis was used to compare cattle production on BMR and PS forage varieties. A curvilinear model with stocking rate and forage variety best fit the data, accounting for 73 and 72% of the variation in ADG and gain per hectare, respectively. At light to moderate stocking rates, ADG and gain per hectare were greater for the BMR; whereas the PS maintained BW gain at greater stocking rates. Our results indicate that cattle grazing these sorghum-sudangrass forages were capable of gaining over 1 kg/steer per day and up to 437 kg/ha over an 84-d grazing season, but response was dependent on forage variety and stocking rate of experimental pastures.