Jameson Brennan, Patricia Johnson, Kenneth Olson, and Jennifer Lutze. Objective
Among management systems intended to increase heterogeneity on the landscape, patch burn grazing (PBG) is by far the most prominent and researched method. Though prescribed burning is seen as a healthy disturbance in grassland ecosystems, many landowners in the Northern Great Plains have an aversion to fire. This is due to safety and liability concerns as well as concerns over forage losses and limitations of labor, equipment, and insurance to successfully carry out prescribed burns. Therefore, there is a critical need to evaluate alternative, non-fire management strategies that will encourage rangeland heterogeneity. A study was conducted in 2017-2018 at the Cottonwood Field Station in southwest South Dakota to test the effectiveness of heavy winter patch grazing to simulate fire. The objectives of this study were to determine the extent to which WPG can serve as an alternative management strategy to patch burn
grazing to 1) increase vegetation structural heterogeneity and 2) alter livestock grazing behavior to maintain structural heterogeneity through time.
Study Description
The study occurred on the SDSU Cottonwood Field Station. Following a wildfire in October 2016 at the field station, the study included three pastures each containing three treatments: a winter grazed patch (WPG), a burned patch (PBG), and an ungrazed control patch (CG). Within each pasture, WPG patches were created by intensively grazing cows during the dormant season in winter of 2016-2017 to reduce standing dead forage to mimic the effects of fire. Vegetation height transects in the spring and satellite imagery converted to NDVI were used to assess the impact of treatments on vegetation structure and greenness. Pastures were grazed by yearling steers in the summer of 2017 and 2018, a subset of which were outfitted with GPS collars to determine grazing locations. Grazing preference indexes were calculated for each treatment in each pasture. Vegetation height, NDVI, and grazing preference index data were analyzed as a random block design with pasture as a block and treatment as a factor. For grazing preference data, an additional factor of time (month) was included in the analysis to test for changes in grazing preference over a season.
Take home points
WPG significantly reduced standing dead vegetation structure by 65% compared to the CG treatment (P < 0.001). In 2017 and 2018, both the WPG and PBG had significantly higher NDVI values compared to the CG treatment (P < 0.05), however no difference was observed between
the PBG and WPG treatments in both years (P > 0.05). Satellite imagery results suggest similar spectral signatures were created by the PBG and WPG treatments, and the treatment effects carried over for 2 years post-disturbance. Analysis of livestock grazing preference showed a significant treatment x time interaction in 2017 (P < 0.001) and a significant treatment effect in 2018 (P < 0.001). Results show winter patch grazing was effective in creating structural
heterogeneity on the landscape; however, livestock showed a higher preference for burned areas over the winter patch when given the choice. In both years the CG treatment was the least preferred area for grazing. Given the unlikelihood of having both treatments in a management strategy, results of this study show heavy winter grazing can be used as a surrogate for fire to create structural heterogeneity and shift grazing on the landscape. Acknowledgements
This research was supported by the SD Agricultural Experiment Station and by grants awarded to South Dakota State University from the USDA NIFA-AFRI (Grant # 2017-67020-26511) and NCR-SARE (Grant # 2015-38640-23781) programs. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors(s) and do not represent the policy or position of SDAES or the USDA.
Beef Day 2020
Cow/Calf
Influence of winter cow feeding strategies on cow response
E. Gubbels, K. Olson, J. Block, Z. Smith, R. Salverson, A. Harty, W. Rusche, J. Grubbs, K. Underwood, C.Wright, C. Schauer, D. Stecher, D. Drolc, A. BlairObjective
The objective of this study was to investigate the effects of the primary maternal prepartum dietary energy source (forage vs. concentrate) during mid- and late-gestation on dam body weight (BW), body condition score (BCS), pregnancy rate, and economic responses.
Study Description
Two experiments were conducted to evaluate alternative winter-feeding strategies when drought limits local feed resources. Under these circumstances, cattle are often transported to locations with less-limiting feed resources. Roughage is available but often expensive at the alternative location, so limit-fed, concentrate-based rations become the least-cost option to meet nutrient requirements of gestating cows.
Experiment 1: Angus x Simmental crossbred cows from the SDSU Antelope Research Station were stratified by BW and age into three treatment groups (n = 48/treatment): Control (winter grazing with protein supplement), Forage-based diet fed in drylot, and limit-fed Concentrate- based diet fed in drylot. Cows in control remained at Antelope and cows in drylot treatments were transported to a commercial drylot facility near Java, SD. Drylot treatment cows were returned to Antelope in late gestation and calved.
Experiment 2: Angus cows from the NDSU Hettinger Research Extension Center were stratified by BW and age into two treatment groups (n = 35/treatment): Forage-based diet or limit-fed Concentrate-based diet fed in drylot. All cows were transported to the drylot facility near Java for winter feeding, then returned to Hettinger in late gestation and calved.
Drylot treatment diets were formulated and fed in amounts so energy (TDN) and crude protein intakes were equal and balanced to maintain BCS during the winter-feeding period. The forage- based diet included 71.9% wheat straw, 21.8% grass/alfalfa hay, 3.7% corn silage, and 2.6% liquid supplement (DM basis). The concentrate-based diet included 56.6% corn grain, 13.3% modified distiller’s grains with solubles, 24.1% wheat straw, 4.6% liquid supplement, and 1.4% limestone (DM basis). In both experiments, BW and BCS were recorded before and after treatment application. Cows were ultrasounded at weaning to determine pregnancy status. All inputs were recorded to calculate economic response to treatments.
Take home points
Data analysis will be conducted to understand the influence of maternal prepartum dietary energy source on cow performance and economic responses.
Acknowledgements
Financial support of this project was provided by state and federal funds appropriated to South Dakota State University including support by the USDA National Institute of Food and
Agriculture, Hatch project (accession no. 1020088).