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

Authors: Gunter, Stacey

Submitted to: American Society of Animal Science Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/25/2019
Publication Date: 12/5/2019
Citation: Gunter, S.A. 2019. Interaction between stocking and supplementation rates on the performance of steers grazing mixed-grass prairie during the winter [Abstract]. Journal of Animal Science. 97(Suppl.3):90. https://doi.org/10.1093/jas/skz258.185.
DOI: https://doi.org/10.1093/jas/skz258.185

Interpretive Summary: To evaluate the effects of stocking and supplementation rates on steers grazing native mixed-grass prairie during the 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 annual stocking rate of 39.4, 33.2, and 29.7 animal-unit-d/ha harvested over 88 d of grazing; the second factor was daily supplementation at 0.9 or 1.4 kg/steer. Steers were fed a 41% crude protein cottonseed meal-based pelleted feed. 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 as 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 (BW) 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.

Technical Abstract: To evaluate the effects of stocking and supplementation rates on steers grazing native mixed-grass prairie during the 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 annual stocking rate of 39.4, 33.2, and 29.7 animal-unit-d/ha harvested over 88 d of grazing; the second factor was daily supplementation at 0.9 or 1.4 kg/steer. Steers were fed a 41% crude protein cottonseed meal-based pelleted feed. 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 as 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 (BW) 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.