263 Interaction between stocking and supplementation rates on the performance of steers grazing mixed-grass prairie during winter

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Abstract To evaluate the effects of stocking and supplementation rates on steers grazing mixed-grass prairie during winter, 16 pastures (10 to 21 ha each) were selected and treatments were arranged in a 3 x 2 factorial design; the first factor was an stocking rate of 39.4, 33.2, and 29.7 animal-unit-d/ha harvested over 88 d of grazing; the second factor was supplementation at 0.9 or 1.4 kg/d. Steers were fed a 43% CP cottonseed meal-based pellet. Pastures were stocked annually in late January (2009, 2010, and 2011) with British x Continental crossbred beef steers (body weight = 202 ± 6.7 kg; n = 137 steers/yr) at stocking densities described above. Data were analyzed by ANOVA with pasture as the experimental unit and year as a random variable; least-squares means were separated with linear and quadratic contrast. From late-January to mid-March, average daily gain (ADG, kg) did not differ (P = 0.13) among stocking rates, but ADG differed (P = 0.01) between 0.9 and 1.4 kg of supplement/d. From mid-March to late-April and over the entire grazing period, ADG responded to stocking rate and interacted (P < 0.01) with supplementation rate; ADG tended to respond quadratically (P ≤ 0.09) to stocking rate at 0.9 kg/d of supplementation, but with 1.4 kg/d of supplement ADG was not affected (P ≥ 0.18). Body weight gain per hectare tended (P < 0.08) to interact between stocking and supplementation rates. With 0.9 kg/d of supplement the BW gain per hectare increased quadratically (P < 0.01) in response to increasing stocking rate, where supplementation at 1.4 kg/d resulted in BW gain per hectare increasing linearly (P < 0.01). Optimal supplementation rates with high-protein feeds is related to stocking rate. At lower stocking rates, less supplement seems to be most beneficial. At higher stocking rates, more supplement is justified.