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

Authors: Gunter, Stacey

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2019
Publication Date: 11/25/2019
Citation: Gunter, S.A. 2019. Effects of stocking and supplementation rates on the performance of steers grazing mixed-grass prairie during the winter. Applied Animal Science. 35:641-651. https://doi.org/10.15232/aas.2019-01864.
DOI: https://doi.org/10.15232/aas.2019-01864

Interpretive Summary: Wise use of our natural resources is paramount to a sustainable and secure food production system. Using rangelands for the grazing of domestic ruminants adds marketable production to farms and feeds rural economies, supplying high-quality foods dense in near-ideal proteins. Mixed grasslands with an overstory of sand sagebrush spreads across nearly 12 million acres of sandy soils on the Southern Great Plains. A large portion of sand-sagebrush grassland is managed primarily for maximum livestock production. Stocking rate is the primary determinate of animal body weight gain and enterprise profitability because the stocking rate effects herbage allowance and herbage quality. However, supplementation with protein or energy feeds may augment animal performance at any stocking rate and permit for greater economic return to producers. Development of management systems to lower wintering costs and increase the net-return to producers ranching on the Southern Plains could allow them to graze their rangelands less heavily during the physiologically critical summer months. Increasing stocking rates during the winter, while warm-season forages are dormant, and increasing supplementation rates, to maintain animal performance, would allow for economies of scale for fixed cost and, hopefully, decreasing the cost of gain. It is believed that optimal supplementation rate is dependent on the stocking rate, but little research has been completed regarding this question with growing cattle, especially on dormant rangelands. The objectives of this experiment were to determine the effects of stocking and supplementation rates on the performance of beef steers grazing dormant mixed-grass prairie and their interaction. This experiment determined that optimal supplementation rates and performance response with a high-protein feed are related to stocking rate. At lower stocking rates, less supplement seems to be most beneficial, while higher rates of supplementation seemed unfruitful. However, at higher stocking rates where forage allowance is more restrictive, more protein supplement is justified evidenced by the linear increase noted in body weight gain per hectare. However, conservative stocking rates are advised when planning a grazing program because of the possibility of drought, the over stocking effects on plant and soil health, and the conservation of wildlife habitat.

Technical Abstract: The objective of this experiment was to evaluate the effects of stocking and supplementation rates on steers grazing native mixed-grass prairie during the winter. To achieve this objective, 16 pastures (10 to 21 hectares 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/hectare for 88 day; the second factor was supplementation at 0.9 or 1.4 kilograms/steer daily. Steers were fed a 43% crude protein cottonseed meal-based pellet. Data were analyzed with an analysis of variance and the pasture was the experimental unit. Average daily gain and body weight per steer over the 88-day grazing period responded to stocking rate and interacted (Probability < 0.01) with supplementation rate; average daily gain and total body weight gain per steer (kilograms) responded quadratically to stocking rate with 0.9 kilograms/day of supplementation (Probability < 0.01; 0.42, 0.57, and 0.47; 40, 48, and 40, respectively), but with 1.4 kilograms/day of supplement they were unaffected (Probability = 0.34; 0.56, 0.53, and 0.51; 48, 48, and 46, respectively). Body weight gain per hectare (kilograms) tended (Probability = 0.08) to interact between stocking and supplementation rates and at 0.9 kilograms/day of supplement the body weight gain per hectare increased quadratically (Probability < 0.01; 24, 32, and 32, respectively) in response to increasing stocking rate, but with 1.4 kilograms/day of supplement body weight gain per hectare responded linearly (Probability < 0.01; 29, 31, and 35, respectively). Optimal supplementation rates with high-protein feeds interacts with stocking rate. At lower stocking rates, less supplement seems to be most beneficial. However, at higher stocking rates more supplement is justified evidenced by the linear increase not on body weight gain per hectare.